This is gcrypt.info, produced by makeinfo version 4.7 from gcrypt.texi.



   This manual is for Libgcrypt (version 1.2.2, 29 July 2005), which is

GNU's library of cryptographic building blocks.



   Copyright (C) 2000, 2002, 2003, 2004 Free Software Foundation, Inc.



     Permission is granted to copy, distribute and/or modify this

     document under the terms of the GNU General Public License as

     published by the Free Software Foundation; either version 2 of the

     License, or (at your option) any later version. The text of the

     license can be found in the section entitled "Copying".



INFO-DIR-SECTION GNU Libraries

START-INFO-DIR-ENTRY

* libgcrypt: (gcrypt).  Cryptographic function library.

END-INFO-DIR-ENTRY





File: gcrypt.info,  Node: Top,  Next: Introduction,  Up: (dir)



The Libgcrypt Library

*********************



This manual is for Libgcrypt (version 1.2.2, 29 July 2005), which is

GNU's library of cryptographic building blocks.



   Copyright (C) 2000, 2002, 2003, 2004 Free Software Foundation, Inc.



     Permission is granted to copy, distribute and/or modify this

     document under the terms of the GNU General Public License as

     published by the Free Software Foundation; either version 2 of the

     License, or (at your option) any later version. The text of the

     license can be found in the section entitled "Copying".



* Menu:



* Introduction::                 What is Libgcrypt.

* Preparation::                  What you should do before using the library.

* Generalities::                 General library functions and data types.

* Handler Functions::            Working with handler functions.

* Symmetric cryptography::       How to use symmetric cryptography.

* Hashing::                      How to use hashing.

* Public Key cryptography (I)::  How to use public key cryptography.

* Public Key cryptography (II):: How to use public key cryptography, alternatively.

* Random Numbers::               How to work with random numbers.

* S-expressions::                How to manage S-expressions.

* MPI library::                  How to work with multi-precision-integers.

* Utilities::                    Utility functions.



Appendices



* Library Copying::             The GNU Lesser General Public License

                                says how you can copy and share `Libgcrypt'.

* Copying::                     The GNU General Public License says how you

                                can copy and share some parts of `Libgcrypt'.



Indices



* Concept Index::               Index of concepts and programs.

* Function and Data Index::     Index of functions, variables and data types.



 --- The Detailed Node Listing ---



Introduction

* Getting Started::             How to use this manual.

* Features::                    A glance at Libgcrypt's features.

* Overview::                    Overview about the library.



Preparation

* Header::                              What header file you need to include.

* Building sources::                    How to build sources using the library.

* Building sources using Automake::     How to build sources with the help of Automake.

* Initializing the library::            How to initialize the library.

* Multi Threading::                     How Libgcrypt can be used in a MT environment.



Generalities

* Controlling the library::     Controlling Libgcrypt's behavior.

* Modules::                     Description of extension modules.

* Error Handling::              Error codes and such.



Handler Functions

* Progress handler::            Using a progress handler function.

* Allocation handler::          Using special memory allocation functions.

* Error handler::               Using error handler functions.

* Logging handler::             Using a special logging function.



Symmetric cryptography

* Available ciphers::           List of ciphers supported by the library.

* Cipher modules::              How to work with cipher modules.

* Available cipher modes::      List of cipher modes supported by the library.

* Working with cipher handles:: How to perform operations related to cipher handles.

* General cipher functions::    General cipher functions independent of cipher handles.



Hashing

* Available hash algorithms::           List of hash algorithms supported by the library.

* Hash algorithm modules::              How to work with hash algorithm modules.

* Working with hash algorithms::        List of functions related to hashing.



Public Key cryptography (I)

* Used S-expressions::                    Introduction into the used S-expression.

* Available algorithms::                  Algorithms supported by the library.

* Public key modules::                    How to work with public key modules.

* Cryptographic Functions::               Functions for performing the cryptographic actions.

* General public-key related Functions::  General functions, not implementing any cryptography.



Public Key cryptography (II)

* Available asymmetric algorithms:: List of algorithms supported by the library.

* Working with sets of data::       How to work with sets of data.

* Working with handles::            How to use handles.

* Working with keys::               How to work with keys.

* Using cryptographic functions::   How to perform cryptographic operations.

* Handle-independent functions::    General functions independent of handles.



Random Numbers

* Quality of random numbers::   Libgcrypt uses different quality levels.

* Retrieving random numbers::   How to retrieve random numbers.



S-expressions

* Data types for S-expressions::   Data types related with S-expressions.

* Working with S-expressions::     How to work with S-expressions.



MPI library

* Data types::                  MPI related data types.

* Basic functions::             First steps with MPI numbers.

* MPI formats::                 External representation of MPIs.

* Calculations::                Performing MPI calculations.

* Comparisons::                 How to compare MPI values.

* Bit manipulations::           How to access single bits of MPI values.

* Miscellaneous::               Miscellaneous MPI functions.



Utilities

* Memory allocation::           Functions related with memory allocation.





File: gcrypt.info,  Node: Introduction,  Next: Preparation,  Prev: Top,  Up: Top



1 Introduction

**************



`Libgcrypt' is a library providing cryptographic building blocks.



* Menu:



* Getting Started::             How to use this manual.

* Features::                    A glance at Libgcrypt's features.

* Overview::                    Overview about the library.





File: gcrypt.info,  Node: Getting Started,  Next: Features,  Up: Introduction



1.1 Getting Started

===================



This manual documents the `Libgcrypt' library application programming

interface (API).  All functions and data types provided by the library

are explained.



The reader is assumed to possess basic knowledge about applied

cryptography.



   This manual can be used in several ways.  If read from the beginning

to the end, it gives a good introduction into the library and how it

can be used in an application.  Forward references are included where

necessary.  Later on, the manual can be used as a reference manual to

get just the information needed about any particular interface of the

library.  Experienced programmers might want to start looking at the

examples at the end of the manual, and then only read up those parts of

the interface which are unclear.





File: gcrypt.info,  Node: Features,  Next: Overview,  Prev: Getting Started,  Up: Introduction



1.2 Features

============



`Libgcrypt' might have a couple of advantages over other libraries doing

a similar job.



It's Free Software

     Anybody can use, modify, and redistribute it under the terms of

     the GNU Lesser General Public License (*note Library Copying::).

     Note, that some parts (which are not needed on a GNU or GNU/Linux

     system) are subject to the terms of the GNU General Public License

     (*note Copying::); please see the README file of the distribution

     for of list of these parts.



It encapsulates the low level cryptography

     `Libgcrypt' provides a high level interface to cryptographic

     building blocks using an extendable and flexible API.







File: gcrypt.info,  Node: Overview,  Prev: Features,  Up: Introduction



1.3 Overview

============



The `Libgcrypt' library is fully thread-safe, where it makes sense to

be thread-safe.  An exception for thread-safety are some cryptographic

functions that modify a certain context stored in handles.  If the user

really intents to use such functions from different threads on the same

handle, he has to take care of the serialization of such functions

himself.  If not described otherwise, every function is thread-safe.



   Libgcrypt depends on the library `libgpg-error', which contains

common error handling related code for GnuPG components.





File: gcrypt.info,  Node: Preparation,  Next: Generalities,  Prev: Introduction,  Up: Top



2 Preparation

*************



To use `Libgcrypt', you have to perform some changes to your sources

and the build system.  The necessary changes are small and explained in

the following sections.  At the end of this chapter, it is described

how the library is initialized, and how the requirements of the library

are verified.



* Menu:



* Header::                      What header file you need to include.

* Building sources::            How to build sources using the library.

* Building sources using Automake::  How to build sources with the help of Automake.

* Initializing the library::    How to initialize the library.

* Multi Threading::             How Libgcrypt can be used in a MT environment.





File: gcrypt.info,  Node: Header,  Next: Building sources,  Up: Preparation



2.1 Header

==========



All interfaces (data types and functions) of the library are defined in

the header file `gcrypt.h'.  You must include this in all source files

using the library, either directly or through some other header file,

like this:



     #include <gcrypt.h>



   The name space of `Libgcrypt' is `gcry_*' for function and type

names and `GCRY*' for other symbols.  In addition the same name

prefixes with one prepended underscore are reserved for internal use

and should never be used by an application.  Furthermore `libgpg-error'

defines functions prefixed with `gpg_' and preprocessor symbols

prefixed with `GPG_'.  Note that Libgcrypt uses libgpg-error, which

uses `gpg_err_*' as name space for function and type names and

`GPG_ERR_*' for other symbols, including all the error codes.





File: gcrypt.info,  Node: Building sources,  Next: Building sources using Automake,  Prev: Header,  Up: Preparation



2.2 Building sources

====================



If you want to compile a source file including the `gcrypt.h' header

file, you must make sure that the compiler can find it in the directory

hierarchy.  This is accomplished by adding the path to the directory in

which the header file is located to the compilers include file search

path (via the `-I' option).



   However, the path to the include file is determined at the time the

source is configured.  To solve this problem, `Libgcrypt' ships with a

small helper program `libgcrypt-config' that knows the path to the

include file and other configuration options.  The options that need to

be added to the compiler invocation at compile time are output by the

`--cflags' option to `libgcrypt-config'.  The following example shows

how it can be used at the command line:



     gcc -c foo.c `libgcrypt-config --cflags`



   Adding the output of `libgcrypt-config --cflags' to the compilers

command line will ensure that the compiler can find the `Libgcrypt'

header file.



   A similar problem occurs when linking the program with the library.

Again, the compiler has to find the library files.  For this to work,

the path to the library files has to be added to the library search path

(via the `-L' option).  For this, the option `--libs' to

`libgcrypt-config' can be used.  For convenience, this option also

outputs all other options that are required to link the program with

the `Libgcrypt' libraries (in particular, the `-lgcrypt' option).  The

example shows how to link `foo.o' with the `Libgcrypt' library to a

program `foo'.



     gcc -o foo foo.o `libgcrypt-config --libs`



   Of course you can also combine both examples to a single command by

specifying both options to `libgcrypt-config':



     gcc -o foo foo.c `libgcrypt-config --cflags --libs`





File: gcrypt.info,  Node: Building sources using Automake,  Next: Initializing the library,  Prev: Building sources,  Up: Preparation



2.3 Building sources using Automake

===================================



It is much easier if you use GNU Automake instead of writing your own

Makefiles.  If you do that you do not have to worry about finding and

invoking the `libgcrypt-config' script at all.  Libgcrypt provides an

extension to Automake that does all the work for you.



 -- Macro: AM_PATH_LIBGCRYPT ([MINIMUM-VERSION], [ACTION-IF-FOUND],

          [ACTION-IF-NOT-FOUND])

     Check whether Libgcrypt (at least version MINIMUM-VERSION, if

     given) exists on the host system.  If it is found, execute

     ACTION-IF-FOUND, otherwise do ACTION-IF-NOT-FOUND, if given.



     Additionally, the function defines `LIBGCRYPT_CFLAGS' to the flags

     needed for compilation of the program to find the `gcrypt.h'

     header file, and `LIBGCRYPT_LIBS' to the linker flags needed to

     link the program to the Libgcrypt library.



   You can use the defined Autoconf variables like this in your

`Makefile.am':



     AM_CPPFLAGS = $(LIBGCRYPT_CFLAGS)

     LDADD = $(LIBGCRYPT_LIBS)





File: gcrypt.info,  Node: Initializing the library,  Next: Multi Threading,  Prev: Building sources using Automake,  Up: Preparation



2.4 Initializing the library

============================



It is often desirable to check that the version of `Libgcrypt' used is

indeed one which fits all requirements.  Even with binary compatibility

new features may have been introduced but due to problem with the

dynamic linker an old version is actually used.  So you may want to

check that the version is okay right after program startup.



 -- Function: const char *gcry_check_version (const char *REQ_VERSION)

     The function `gcry_check_version' has three purposes.  It can be

     used to retrieve the version number of the library.  In addition it

     can verify that the version number is higher than a certain

     required version number.



     In either case, the function initializes some sub-systems, and for

     this reason alone it must be invoked early in your program, before

     you make use of the other functions of Libgcrypt.





File: gcrypt.info,  Node: Multi Threading,  Prev: Initializing the library,  Up: Preparation



2.5 Multi Threading

===================



As mentioned earlier, the `Libgcrypt' library is thread-safe if you

adhere to the following requirements:



   * If your application is multi-threaded, you must set the thread

     support callbacks with the `GCRYCTL_SET_THREAD_CBS' command

     *before* any other function in the library.



     This is easy enough if you are indeed writing an application using

     Libgcrypt.  It is rather problematic if you are writing a library

     instead.  Here are some tips what to do if you are writing a

     library:



     If your library requires a certain thread package, just initialize

     Libgcrypt to use this thread package.  If your library supports

     multiple thread packages, but needs to be configured, you will

     have to implement a way to determine which thread package the

     application wants to use with your library anyway.  Then configure

     Libgcrypt to use this thread package.



     If your library is fully reentrant without any special support by a

     thread package, then you are lucky indeed.  Unfortunately, this

     does not relieve you from doing either of the two above, or use a

     third option.  The third option is to let the application

     initialize Libgcrypt for you.  Then you are not using Libgcrypt

     transparently, though.



     As if this was not difficult enough, a conflict may arise if two

     libraries try to initialize Libgcrypt independently of each

     others, and both such libraries are then linked into the same

     application.  To make it a bit simpler for you, this will probably

     work, but only if both libraries have the same requirement for the

     thread package.  This is currently only supported for the

     non-threaded case, GNU Pth and pthread.  Support for more thread

     packages is easy to add, so contact us if you require it.



   * The function `gcry_check_version' must be called before any other

     function in the library, except the `GCRYCTL_SET_THREAD_CBS'

     command (called via the `gcry_control' function), because it

     initializes the thread support subsystem in Libgcrypt.  To achieve

     this in multi-threaded programs, you must synchronize the memory

     with respect to other threads that also want to use Libgcrypt.

     For this, it is sufficient to call `gcry_check_version' before

     creating the other threads using Libgcrypt(1).



   *  As with the function `gpg_strerror', `gcry_strerror' is not

     thread safe.  You have to use `gpg_strerror_r' instead.



   Libgcrypt contains convenient macros, which define the necessary

thread callbacks for PThread and for GNU Pth:



`GCRY_THREAD_OPTION_PTH_IMPL'

     This macro defines the following (static) symbols: gcry_pth_init,

     gcry_pth_mutex_init, gcry_pth_mutex_destroy, gcry_pth_mutex_lock,

     gcry_pth_mutex_unlock, gcry_pth_read, gcry_pth_write,

     gcry_pth_select, gcry_pth_waitpid, gcry_pth_accept,

     gcry_pth_connect, gcry_threads_pth.



     After including this macro, gcry_control() shall be used with a

     command of GCRYCTL_SET_THREAD_CBS in order to register the thread

     callback structure named "gcry_threads_pth".



`GCRY_THREAD_OPTION_PTHREAD_IMPL'

     This macro defines the following (static) symbols:

     gcry_pthread_mutex_init, gcry_pthread_mutex_destroy,

     gcry_mutex_lock, gcry_mutex_unlock, gcry_threads_pthread.



     After including this macro, gcry_control() shall be used with a

     command of GCRYCTL_SET_THREAD_CBS in order to register the thread

     callback structure named "gcry_threads_pthread".



   Note that these macros need to be terminated with a semicolon.  Keep

in mind that these are convenient macros for C programmers; C++

programmers might have to wrap these macros in an "extern C" body.



   ---------- Footnotes ----------



   (1) At least this is true for POSIX threads, as `pthread_create' is

a function that synchronizes memory with respects to other threads.

There are many functions which have this property, a complete list can

be found in POSIX, IEEE Std 1003.1-2003, Base Definitions, Issue 6, in

the definition of the term "Memory Synchronization".  For other thread

packages, more relaxed or more strict rules may apply.





File: gcrypt.info,  Node: Generalities,  Next: Handler Functions,  Prev: Preparation,  Up: Top



3 Generalities

**************



* Menu:



* Controlling the library::     Controlling Libgcrypt's behavior.

* Modules::                     Description of extension modules.

* Error Handling::              Error codes and such.





File: gcrypt.info,  Node: Controlling the library,  Next: Modules,  Up: Generalities



3.1 Controlling the library

===========================



 -- Function: gcry_error_t gcry_control (enum gcry_ctl_cmds CMD, ...)

     This function can be used to influence the general behavior of

     Libgcrypt in several ways.  Depending on CMD, more arguments can

     or have to be provided.







File: gcrypt.info,  Node: Modules,  Next: Error Handling,  Prev: Controlling the library,  Up: Generalities



3.2 Modules

===========



Libgcrypt supports the use of `extension modules', which implement

algorithms in addition to those already built into the library directly.



 -- Data type: gcry_module_t

     This data type represents a `module'.



   Functions registering modules provided by the user take a `module

specification structure' as input and return a value of `gcry_module_t'

and an ID that is unique in the modules' category.  This ID can be used

to reference the newly registered module.  After registering a module

successfully, the new functionality should be able to be used through

the normal functions provided by Libgcrypt until it is unregistered

again.





File: gcrypt.info,  Node: Error Handling,  Prev: Modules,  Up: Generalities



3.3 Error Handling

==================



Many functions in Libgcrypt can return an error if they fail.  For this

reason, the application should always catch the error condition and

take appropriate measures, for example by releasing the resources and

passing the error up to the caller, or by displaying a descriptive

message to the user and cancelling the operation.



   Some error values do not indicate a system error or an error in the

operation, but the result of an operation that failed properly.  For

example, if you try to decrypt a tempered message, the decryption will

fail.  Another error value actually means that the end of a data buffer

or list has been reached.  The following descriptions explain for many

error codes what they mean usually.  Some error values have specific

meanings if returned by a certain functions.  Such cases are described

in the documentation of those functions.



   Libgcrypt uses the `libgpg-error' library.  This allows to share the

error codes with other components of the GnuPG system, and thus pass

error values transparently from the crypto engine, or some helper

application of the crypto engine, to the user.  This way no information

is lost.  As a consequence, Libgcrypt does not use its own identifiers

for error codes, but uses those provided by `libgpg-error'.  They

usually start with `GPG_ERR_'.



   However, Libgcrypt does provide aliases for the functions defined in

libgpg-error, which might be preferred for name space consistency.



   Most functions in Libgcrypt return an error code in the case of

failure.  For this reason, the application should always catch the

error condition and take appropriate measures, for example by releasing

the resources and passing the error up to the caller, or by displaying

a descriptive message to the user and canceling the operation.



   Some error values do not indicate a system error or an error in the

operation, but the result of an operation that failed properly.



   GnuPG components, including Libgcrypt, use an extra library named

libgpg-error to provide a common error handling scheme.  For more

information on libgpg-error, see the according manual.



* Menu:



* Error Values::                The error value and what it means.

* Error Sources::               A list of important error sources.

* Error Codes::                 A list of important error codes.

* Error Strings::               How to get a descriptive string from a value.





File: gcrypt.info,  Node: Error Values,  Next: Error Sources,  Up: Error Handling



3.3.1 Error Values

------------------



 -- Data type: gcry_err_code_t

     The `gcry_err_code_t' type is an alias for the `libgpg-error' type

     `gpg_err_code_t'.  The error code indicates the type of an error,

     or the reason why an operation failed.



     A list of important error codes can be found in the next section.



 -- Data type: gcry_err_source_t

     The `gcry_err_source_t' type is an alias for the `libgpg-error'

     type `gpg_err_source_t'.  The error source has not a precisely

     defined meaning.  Sometimes it is the place where the error

     happened, sometimes it is the place where an error was encoded

     into an error value.  Usually the error source will give an

     indication to where to look for the problem.  This is not always

     true, but it is attempted to achieve this goal.



     A list of important error sources can be found in the next section.



 -- Data type: gcry_error_t

     The `gcry_error_t' type is an alias for the `libgpg-error' type

     `gpg_error_t'.  An error value like this has always two

     components, an error code and an error source.  Both together form

     the error value.



     Thus, the error value can not be directly compared against an error

     code, but the accessor functions described below must be used.

     However, it is guaranteed that only 0 is used to indicate success

     (`GPG_ERR_NO_ERROR'), and that in this case all other parts of the

     error value are set to 0, too.



     Note that in Libgcrypt, the error source is used purely for

     diagnostic purposes.  Only the error code should be checked to test

     for a certain outcome of a function.  The manual only documents the

     error code part of an error value.  The error source is left

     unspecified and might be anything.



 -- Function: gcry_err_code_t gcry_err_code (gcry_error_t ERR)

     The static inline function `gcry_err_code' returns the

     `gcry_err_code_t' component of the error value ERR.  This function

     must be used to extract the error code from an error value in

     order to compare it with the `GPG_ERR_*' error code macros.



 -- Function: gcry_err_source_t gcry_err_source (gcry_error_t ERR)

     The static inline function `gcry_err_source' returns the

     `gcry_err_source_t' component of the error value ERR.  This

     function must be used to extract the error source from an error

     value in order to compare it with the `GPG_ERR_SOURCE_*' error

     source macros.



 -- Function: gcry_error_t gcry_err_make (gcry_err_source_t SOURCE,

          gcry_err_code_t CODE)

     The static inline function `gcry_err_make' returns the error value

     consisting of the error source SOURCE and the error code CODE.



     This function can be used in callback functions to construct an

     error value to return it to the library.



 -- Function: gcry_error_t gcry_error (gcry_err_code_t CODE)

     The static inline function `gcry_error' returns the error value

     consisting of the default error source and the error code CODE.



     For GCRY applications, the default error source is

     `GPG_ERR_SOURCE_USER_1'.  You can define `GCRY_ERR_SOURCE_DEFAULT'

     before including `gcrypt.h' to change this default.



     This function can be used in callback functions to construct an

     error value to return it to the library.



   The `libgpg-error' library provides error codes for all system error

numbers it knows about.  If ERR is an unknown error number, the error

code `GPG_ERR_UNKNOWN_ERRNO' is used.  The following functions can be

used to construct error values from system errno numbers.



 -- Function: gcry_error_t gcry_err_make_from_errno

          (gcry_err_source_t SOURCE, int ERR)

     The function `gcry_err_make_from_errno' is like `gcry_err_make',

     but it takes a system error like `errno' instead of a

     `gcry_err_code_t' error code.



 -- Function: gcry_error_t gcry_error_from_errno (int ERR)

     The function `gcry_error_from_errno' is like `gcry_error', but it

     takes a system error like `errno' instead of a `gcry_err_code_t'

     error code.



   Sometimes you might want to map system error numbers to error codes

directly, or map an error code representing a system error back to the

system error number.  The following functions can be used to do that.



 -- Function: gcry_err_code_t gcry_err_code_from_errno (int ERR)

     The function `gcry_err_code_from_errno' returns the error code for

     the system error ERR.  If ERR is not a known system error, the

     function returns `GPG_ERR_UNKNOWN_ERRNO'.



 -- Function: int gcry_err_code_to_errno (gcry_err_code_t ERR)

     The function `gcry_err_code_to_errno' returns the system error for

     the error code ERR.  If ERR is not an error code representing a

     system error, or if this system error is not defined on this

     system, the function returns `0'.





File: gcrypt.info,  Node: Error Sources,  Next: Error Codes,  Prev: Error Values,  Up: Error Handling



3.3.2 Error Sources

-------------------



The library `libgpg-error' defines an error source for every component

of the GnuPG system.  The error source part of an error value is not

well defined.  As such it is mainly useful to improve the diagnostic

error message for the user.



   If the error code part of an error value is `0', the whole error

value will be `0'.  In this case the error source part is of course

`GPG_ERR_SOURCE_UNKNOWN'.



   The list of error sources that might occur in applications using

Libgctypt is:



`GPG_ERR_SOURCE_UNKNOWN'

     The error source is not known.  The value of this error source is

     `0'.



`GPG_ERR_SOURCE_GPGME'

     The error source is GPGME itself.



`GPG_ERR_SOURCE_GPG'

     The error source is GnuPG, which is the crypto engine used for the

     OpenPGP protocol.



`GPG_ERR_SOURCE_GPGSM'

     The error source is GPGSM, which is the crypto engine used for the

     OpenPGP protocol.



`GPG_ERR_SOURCE_GCRYPT'

     The error source is `libgcrypt', which is used by crypto engines

     to perform cryptographic operations.



`GPG_ERR_SOURCE_GPGAGENT'

     The error source is `gpg-agent', which is used by crypto engines

     to perform operations with the secret key.



`GPG_ERR_SOURCE_PINENTRY'

     The error source is `pinentry', which is used by `gpg-agent' to

     query the passphrase to unlock a secret key.



`GPG_ERR_SOURCE_SCD'

     The error source is the SmartCard Daemon, which is used by

     `gpg-agent' to delegate operations with the secret key to a

     SmartCard.



`GPG_ERR_SOURCE_KEYBOX'

     The error source is `libkbx', a library used by the crypto engines

     to manage local keyrings.



`GPG_ERR_SOURCE_USER_1'



`GPG_ERR_SOURCE_USER_2'



`GPG_ERR_SOURCE_USER_3'



`GPG_ERR_SOURCE_USER_4'

     These error sources are not used by any GnuPG component and can be

     used by other software.  For example, applications using Libgcrypt

     can use them to mark error values coming from callback handlers.

     Thus `GPG_ERR_SOURCE_USER_1' is the default for errors created

     with `gcry_error' and `gcry_error_from_errno', unless you define

     `GCRY_ERR_SOURCE_DEFAULT' before including `gcrypt.h'.





File: gcrypt.info,  Node: Error Codes,  Next: Error Strings,  Prev: Error Sources,  Up: Error Handling



3.3.3 Error Codes

-----------------



The library `libgpg-error' defines many error values.  The following

list includes the most important error codes.



`GPG_ERR_EOF'

     This value indicates the end of a list, buffer or file.



`GPG_ERR_NO_ERROR'

     This value indicates success.  The value of this error code is

     `0'.  Also, it is guaranteed that an error value made from the

     error code `0' will be `0' itself (as a whole).  This means that

     the error source information is lost for this error code, however,

     as this error code indicates that no error occured, this is

     generally not a problem.



`GPG_ERR_GENERAL'

     This value means that something went wrong, but either there is not

     enough information about the problem to return a more useful error

     value, or there is no separate error value for this type of

     problem.



`GPG_ERR_ENOMEM'

     This value means that an out-of-memory condition occurred.



`GPG_ERR_E...'

     System errors are mapped to GPG_ERR_EFOO where FOO is the symbol

     for the system error.



`GPG_ERR_INV_VALUE'

     This value means that some user provided data was out of range.



`GPG_ERR_UNUSABLE_PUBKEY'

     This value means that some recipients for a message were invalid.



`GPG_ERR_UNUSABLE_SECKEY'

     This value means that some signers were invalid.



`GPG_ERR_NO_DATA'

     This value means that data was expected where no data was found.



`GPG_ERR_CONFLICT'

     This value means that a conflict of some sort occurred.



`GPG_ERR_NOT_IMPLEMENTED'

     This value indicates that the specific function (or operation) is

     not implemented.  This error should never happen.  It can only

     occur if you use certain values or configuration options which do

     not work, but for which we think that they should work at some

     later time.



`GPG_ERR_DECRYPT_FAILED'

     This value indicates that a decryption operation was unsuccessful.



`GPG_ERR_WRONG_KEY_USAGE'

     This value indicates that a key is not used appropriately.



`GPG_ERR_NO_SECKEY'

     This value indicates that no secret key for the user ID is

     available.



`GPG_ERR_UNSUPPORTED_ALGORITHM'

     This value means a verification failed because the cryptographic

     algorithm is not supported by the crypto backend.



`GPG_ERR_BAD_SIGNATURE'

     This value means a verification failed because the signature is

     bad.



`GPG_ERR_NO_PUBKEY'

     This value means a verification failed because the public key is

     not available.



`GPG_ERR_USER_1'



`GPG_ERR_USER_2'



`...'



`GPG_ERR_USER_16'

     These error codes are not used by any GnuPG component and can be

     freely used by other software.  Applications using Libgcrypt might

     use them to mark specific errors returned by callback handlers if

     no suitable error codes (including the system errors) for these

     errors exist already.





File: gcrypt.info,  Node: Error Strings,  Prev: Error Codes,  Up: Error Handling



3.3.4 Error Strings

-------------------



 -- Function: const char * gcry_strerror (gcry_error_t ERR)

     The function `gcry_strerror' returns a pointer to a statically

     allocated string containing a description of the error code

     contained in the error value ERR.  This string can be used to

     output a diagnostic message to the user.



 -- Function: const char * gcry_strsource (gcry_error_t ERR)

     The function `gcry_strerror' returns a pointer to a statically

     allocated string containing a description of the error source

     contained in the error value ERR.  This string can be used to

     output a diagnostic message to the user.



   The following example illustrates the use of the functions described

above:



     {

       gcry_cipher_hd_t handle;

       gcry_error_t err = 0;



       err = gcry_cipher_open (&handle, GCRY_CIPHER_AES, GCRY_CIPHER_MODE_CBC, 0);

       if (err)

         {

           fprintf (stderr, "Failure: %s/%s\n",

                    gcry_strsource (err),

                    gcry_strerror (err));

         }

     }





File: gcrypt.info,  Node: Handler Functions,  Next: Symmetric cryptography,  Prev: Generalities,  Up: Top



4 Handler Functions

*******************



Libgcrypt makes it possible to install so called `handler functions',

which get called by Libgcrypt in case of certain events.



* Menu:



* Progress handler::            Using a progress handler function.

* Allocation handler::          Using special memory allocation functions.

* Error handler::               Using error handler functions.

* Logging handler::             Using a special logging function.





File: gcrypt.info,  Node: Progress handler,  Next: Allocation handler,  Up: Handler Functions



4.1 Progress handler

====================



It is often useful to retrieve some feedback while long running

operations are performed.



 -- Data type: gcry_handler_progress_t

     Progress handler functions have to be of the type

     `gcry_handler_progress_t', which is defined as:



     `void (*gcry_handler_progress_t) (void *, const char *, int, int,

     int)'



   The following function may be used to register a handler function for

this purpose.



 -- Function: void gcry_set_progress_handler (gcry_handler_progress_t

          CB, void *CB_DATA)

     This function installs CB as the `Progress handler' function.  CB

     must be defined as follows:



          void

          my_progress_handler (void *CB_DATA, const char *WHAT,

                               int PRINTCHAR, int CURRENT, int TOTAL)

          {

            /* Do something.  */

          }



     A description of the arguments of the progress handler function

     follows.



    CB_DATA

          The argument provided in the call to

          `gcry_set_progress_handler'.



    WHAT

          A string identifying the type of the progress output.  The

          following values for WHAT are defined:



         `need_entropy'

               Not enough entropy is available.  TOTAL holds the number

               of required bytes.



         `primegen'

               Values for PRINTCHAR:

              `\n'

                    Prime generated.



              `!'

                    Need to refresh the pool of prime numbers.



              `<, >'

                    Number of bits adjusted.



              `^'

                    Searching for a generator.



              `.'

                    Fermat test on 10 candidates failed.



              `:'

                    Restart with a new random value.



              `+'

                    Rabin Miller test passed.









File: gcrypt.info,  Node: Allocation handler,  Next: Error handler,  Prev: Progress handler,  Up: Handler Functions



4.2 Allocation handler

======================



It is possible to make Libgcrypt use special memory allocation

functions instead of the built-in ones.



   Memory allocation functions are of the following types:



 -- Data type: gcry_handler_alloc_t

     This type is defined as: `void *(*gcry_handler_alloc_t) (size_t

     n)'.



 -- Data type: gcry_handler_secure_check_t

     This type is defined as: `int *(*gcry_handler_secure_check_t)

     (const void *)'.



 -- Data type: gcry_handler_realloc_t

     This type is defined as: `void *(*gcry_handler_realloc_t) (void

     *p, size_t n)'.



 -- Data type: gcry_handler_free_t

     This type is defined as: `void *(*gcry_handler_free_t) (void *)'.



   Special memory allocation functions can be installed with the

following function:



 -- Function: void gcry_set_allocation_handler (gcry_handler_alloc_t

          FUNC_ALLOC, gcry_handler_alloc_t FUNC_ALLOC_SECURE,

          gcry_handler_secure_check_t FUNC_SECURE_CHECK,

          gcry_handler_realloc_t FUNC_REALLOC, gcry_handler_free_t

          FUNC_FREE)

     Install the provided functions and use them instead of the built-in

     functions for doing memory allocation.





File: gcrypt.info,  Node: Error handler,  Next: Logging handler,  Prev: Allocation handler,  Up: Handler Functions



4.3 Error handler

=================



The following functions may be used to register handler functions that

are called by Libgcrypt in case certain error conditions occur.



 -- Data type: gcry_handler_no_mem_t

     This type is defined as: `void (*gcry_handler_no_mem_t) (void *,

     size_t, unsigned int)'



 -- Function: void gcry_set_outofcore_handler (gcry_handler_no_mem_t

          FUNC_NO_MEM, void *CB_DATA)

     This function registers FUNC_NO_MEM as `out-of-core handler',

     which means that it will be called in the case of not having enough

     memory available.



 -- Data type: gcry_handler_error_t

     This type is defined as: `void (*gcry_handler_error_t) (void *,

     int, const char *)'



 -- Function: void gcry_set_fatalerror_handler (gcry_handler_error_t

          FUNC_ERROR, void *CB_DATA)

     This function registers FUNC_ERROR as `error handler', which means

     that it will be called in error conditions.





File: gcrypt.info,  Node: Logging handler,  Prev: Error handler,  Up: Handler Functions



4.4 Logging handler

===================



 -- Data type: gcry_handler_log_t

     This type is defined as: `void (*gcry_handler_log_t) (void *, int,

     const char *, va_list)'



 -- Function: void gcry_set_log_handler (gcry_handler_log_t FUNC_LOG,

          void *CB_DATA)

     This function registers FUNC_LOG as `logging handler', which means

     that it will be called in case Libgcrypt wants to log a message.





File: gcrypt.info,  Node: Symmetric cryptography,  Next: Hashing,  Prev: Handler Functions,  Up: Top



5 Symmetric cryptography

************************



The cipher functions are used for symmetrical cryptography, i.e.

cryptography using a shared key.  The programming model follows an

open/process/close paradigm and is in that similar to other building

blocks provided by Libgcrypt.



* Menu:



* Available ciphers::           List of ciphers supported by the library.

* Cipher modules::              How to work with cipher modules.

* Available cipher modes::      List of cipher modes supported by the library.

* Working with cipher handles::  How to perform operations related to cipher handles.

* General cipher functions::    General cipher functions independent of cipher handles.





File: gcrypt.info,  Node: Available ciphers,  Next: Cipher modules,  Up: Symmetric cryptography



5.1 Available ciphers

=====================



`GCRY_CIPHER_NONE'

     This is not a real algorithm but used by some functions as error

     return.  The value always evaluates to false.



`GCRY_CIPHER_IDEA'

     This is the IDEA algorithm.  The constant is provided but there is

     currently no implementation for it because the algorithm is

     patented.



`GCRY_CIPHER_3DES'

     Triple-DES with 3 Keys as EDE.  The key size of this algorithm is

     168 but you have to pass 192 bits because the most significant

     bits of each byte are ignored.



`GCRY_CIPHER_CAST5'

     CAST128-5 block cipher algorithm.  The key size is 128 bits.



`GCRY_CIPHER_BLOWFISH'

     The blowfish algorithm. The current implementation allows only for

     a key size of 128 bits.



`GCRY_CIPHER_SAFER_SK128'

     Reserved and not currently implemented.



`GCRY_CIPHER_DES_SK'

     Reserved and not currently implemented.



`GCRY_CIPHER_AES'

`GCRY_CIPHER_AES128'

`GCRY_CIPHER_RIJNDAEL'

`GCRY_CIPHER_RIJNDAEL128'

     AES (Rijndael) with a 128 bit key.



`GCRY_CIPHER_AES192'

`GCRY_CIPHER_RIJNDAEL128'

     AES (Rijndael) with a 192 bit key.



`GCRY_CIPHER_AES256'

`GCRY_CIPHER_RIJNDAEL256'

     AES (Rijndael) with a 256 bit key.



`GCRY_CIPHER_TWOFISH'

     The Twofish algorithm with a 256 bit key.



`GCRY_CIPHER_TWOFISH128'

     The Twofish algorithm with a 128 bit key.



`GCRY_CIPHER_ARCFOUR'

     An algorithm which is 100% compatible with RSA Inc.'s RC4

     algorithm.  Note that this is a stream cipher and must be used

     very carefully to avoid a couple of weaknesses.



`GCRY_CIPHER_DES'

     Standard DES with a 56 bit key. You need to pass 64 bit but the

     high bits of each byte are ignored.  Note, that this is a weak

     algorithm which can be broken in reasonable time using a brute

     force approach.







File: gcrypt.info,  Node: Cipher modules,  Next: Available cipher modes,  Prev: Available ciphers,  Up: Symmetric cryptography



5.2 Cipher modules

==================



Libgcrypt makes it possible to load additional `cipher modules'; these

cipher can be used just like the cipher algorithms that are built into

the library directly.  For an introduction into extension modules, see

*Note Modules::.



 -- Data type: gcry_cipher_spec_t

     This is the `module specification structure' needed for registering

     cipher modules, which has to be filled in by the user before it

     can be used to register a module.  It contains the following

     members:



    `const char *name'

          The primary name of the algorithm.



    `const char **aliases'

          A list of strings that are `aliases' for the algorithm.  The

          list must be terminated with a NULL element.



    `gcry_cipher_oid_spec_t *oids'

          A list of OIDs that are to be associated with the algorithm.

          The list's last element must have it's `oid' member set to

          NULL.  See below for an explanation of this type.



    `size_t blocksize'

          The block size of the algorithm, in bytes.



    `size_t keylen'

          The length of the key, in bits.



    `size_t contextsize'

          The size of the algorithm-specific `context', that should be

          allocated for each handle.



    `gcry_cipher_setkey_t setkey'

          The function responsible for initializing a handle with a

          provided key.  See below for a description of this type.



    `gcry_cipher_encrypt_t encrypt'

          The function responsible for encrypting a single block.  See

          below for a description of this type.



    `gcry_cipher_decrypt_t decrypt'

          The function responsible for decrypting a single block.  See

          below for a description of this type.



    `gcry_cipher_stencrypt_t stencrypt'

          Like `encrypt', for stream ciphers.  See below for a

          description of this type.



    `gcry_cipher_stdecrypt_t stdecrypt'

          Like `decrypt', for stream ciphers.  See below for a

          description of this type.



 -- Data type: gcry_cipher_oid_spec_t

     This type is used for associating a user-provided algorithm

     implementation with certain OIDs.  It contains the following

     members:

    `const char *oid'

          Textual representation of the OID.



    `int mode'

          Cipher mode for which this OID is valid.



 -- Data type: gcry_cipher_setkey_t

     Type for the `setkey' function, defined as: gcry_err_code_t

     (*gcry_cipher_setkey_t) (void *c, const unsigned char *key,

     unsigned keylen)



 -- Data type: gcry_cipher_encrypt_t

     Type for the `encrypt' function, defined as: gcry_err_code_t

     (*gcry_cipher_encrypt_t) (void *c, const unsigned char *outbuf,

     const unsigned char *inbuf)



 -- Data type: gcry_cipher_decrypt_t

     Type for the `decrypt' function, defined as: gcry_err_code_t

     (*gcry_cipher_decrypt_t) (void *c, const unsigned char *outbuf,

     const unsigned char *inbuf)



 -- Data type: gcry_cipher_stencrypt_t

     Type for the `stencrypt' function, defined as: gcry_err_code_t

     (*gcry_cipher_stencrypt_t) (void *c, const unsigned char *outbuf,

     const unsigned char *, unsigned int n)



 -- Data type: gcry_cipher_stdecrypt_t

     Type for the `stdecrypt' function, defined as: gcry_err_code_t

     (*gcry_cipher_stdecrypt_t) (void *c, const unsigned char *outbuf,

     const unsigned char *, unsigned int n)



 -- Function: gcry_error_t gcry_cipher_register (gcry_cipher_spec_t

          *CIPHER, unsigned int *algorithm_id, gcry_module_t *MODULE)

     Register a new cipher module whose specification can be found in

     CIPHER.  On success, a new algorithm ID is stored in ALGORITHM_ID

     and a pointer representing this module is stored in MODULE.



 -- Function: void gcry_cipher_unregister (gcry_module_t MODULE)

     Unregister the cipher identified by MODULE, which must have been

     registered with gcry_cipher_register.



 -- Function: gcry_error_t gcry_cipher_list (int *LIST, int

          *LIST_LENGTH)

     Get a list consisting of the IDs of the loaded cipher modules.  If

     LIST is zero, write the number of loaded cipher modules to

     LIST_LENGTH and return.  If LIST is non-zero, the first

     *LIST_LENGTH algorithm IDs are stored in LIST, which must be of

     according size.  In case there are less cipher modules than

     *LIST_LENGTH, *LIST_LENGTH is updated to the correct number.





File: gcrypt.info,  Node: Available cipher modes,  Next: Working with cipher handles,  Prev: Cipher modules,  Up: Symmetric cryptography



5.3 Available cipher modes

==========================



`GCRY_CIPHER_MODE_NONE'

     No mode specified, may be set later using other functions.  The

     value of this constant is always 0.



`GCRY_CIPHER_MODE_ECB'

     Electronic Codebook mode.



`GCRY_CIPHER_MODE_CFB'

     Cipher Feedback mode.



`GCRY_CIPHER_MODE_CBC'

     Cipher Block Chaining mode.



`GCRY_CIPHER_MODE_STREAM'

     Stream mode, only to be used with stream cipher algorithms.



`GCRY_CIPHER_MODE_OFB'

     Outer Feedback mode.



`GCRY_CIPHER_MODE_CTR'

     Counter mode.







File: gcrypt.info,  Node: Working with cipher handles,  Next: General cipher functions,  Prev: Available cipher modes,  Up: Symmetric cryptography



5.4 Working with cipher handles

===============================



To use a cipher algorithm, you must first allocate an according handle.

This is to be done using the open function:



 -- Function: gcry_error_t gcry_cipher_open (gcry_cipher_hd_t *HD, int

          ALGO, int MODE, unsigned int FLAGS)

     This function creates the context handle required for most of the

     other cipher functions and returns a handle to it in `hd'.  In

     case of an error, an according error code is returned.



     The ID of algorithm to use must be specified via ALGO.  See *Note

     Available ciphers::, for a list of supported ciphers and the

     according constants.



     Besides using the constants directly, the function

     `gcry_cipher_map_name' may be used to convert the textual name of

     an algorithm into the according numeric ID.



     The cipher mode to use must be specified via MODE.  See *Note

     Available cipher modes::, for a list of supported cipher modes and

     the according constants.  Note, that some modes do not work

     together with all algorithms.



     The third argument FLAGS can either be passed as `0' or as the

     bit-wise OR of the following constants.



    `GCRY_CIPHER_SECURE'

          Make sure that all operations are allocated in secure memory.

          This is useful, when the key material is highly confidential.



    `GCRY_CIPHER_ENABLE_SYNC'

          This flag enables the CFB sync mode, which is a special

          feature of Libgcrypt's CFB mode implementation to allow for

          OpenPGP's CFB variant.  See `gcry_cipher_sync'.



    `GCRY_CIPHER_CBC_CTS'

          Enable cipher text stealing (CTS) for the CBC mode.  Cannot

          be used simultaneous as GCRY_CIPHER_CBC_MAC



    `GCRY_CIPHER_CBC_MAC'

          Compute CBC-MAC keyed checksums.  This is the same as CBC

          mode, but only output the last block.  Cannot be used

          simultaneous as GCRY_CIPHER_CBC_CTS.



   Use the following function to release an existing handle:



 -- Function: void gcry_cipher_close (gcry_cipher_hd_t H)

     This function releases the context created by `gcry_cipher_open'.



   In order to use a handle for performing cryptographic operations, a

`key' has to be set first:



 -- Function: gcry_error_t gcry_cipher_setkey (gcry_cipher_hd_t H, void

          *K, size_t L)

     Set the key K used for encryption or decryption in the context

     denoted by the handle H.  The length L of the key K must match the

     required length of the algorithm set for this context or be in the

     allowed range for algorithms with variable key size.  The function

     checks this and returns an error if there is a problem.  A caller

     should always check for an error.



     Note, this is currently implemented as a macro but may be changed

     to a function in the future.



   Most crypto modes requires an initialization vector (IV), which

usually is a non-secret random string acting as a kind of salt value.

The CTR mode requires a counter, which is also similar to a salt value.

To set the IV or CTR, use these functions:



 -- Function: gcry_error_t gcry_cipher_setiv (gcry_cipher_hd_t H, void

          *K, size_t L)

     Set the initialization vector used for encryption or decryption.

     The vector is passed as the buffer K of length L and copied to

     internal data structures.  The function checks that the IV matches

     the requirement of the selected algorithm and mode.  Note, that

     this is implemented as a macro.



 -- Function: gcry_error_t gcry_cipher_setctr (gcry_cipher_hd_t H, void

          *C, size_t L)

     Set the counter vector used for encryption or decryption. The

     counter is passed as the buffer C of length L and copied to

     internal data structures.  The function checks that the counter

     matches the requirement of the selected algorithm (i.e., it must be

     the same size as the block size).  Note, that this is implemented

     as a macro.



 -- Function: gcry_error_t gcry_cipher_reset (gcry_cipher_hd_t H)

     Set the given handle's context back to the state it had after the

     last call to gcry_cipher_setkey and clear the initialization

     vector.



     Note, that gcry_cipher_reset is implemented as a macro.



   The actual encryption and decryption is done by using one of the

following functions.  They may be used as often as required to process

all the data.



 -- Function: gcry_error_t gcry_cipher_encrypt (gcry_cipher_hd_t H,

          void *out, size_t OUTSIZE, const void *IN, size_t INLEN)

     `gcry_cipher_encrypt' is used to encrypt the data.  This function

     can either work in place or with two buffers.  It uses the cipher

     context already setup and described by the handle H.  There are 2

     ways to use the function: If IN is passed as `NULL' and INLEN is

     `0', in-place encryption of the data in OUT or length OUTSIZE

     takes place.  With IN being not `NULL', INLEN bytes are encrypted

     to the buffer OUT which must have at least a size of INLEN.

     OUTLEN must be set to the allocated size of OUT, so that the

     function can check that there is sufficient space. Note, that

     overlapping buffers are not allowed.



     Depending on the selected algorithms and encryption mode, the

     length of the buffers must be a multiple of the block size.



     The function returns `0' on success or an error code.



 -- Function: gcry_error_t gcry_cipher_decrypt (gcry_cipher_hd_t H,

          void *out, size_t OUTSIZE, const void *IN, size_t INLEN)

     `gcry_cipher_decrypt' is used to decrypt the data.  This function

     can either work in place or with two buffers.  It uses the cipher

     context already setup and described by the handle H.  There are 2

     ways to use the function: If IN is passed as `NULL' and INLEN is

     `0', in-place decryption of the data in OUT or length OUTSIZE

     takes place.  With IN being not `NULL', INLEN bytes are decrypted

     to the buffer OUT which must have at least a size of INLEN.

     OUTLEN must be set to the allocated size of OUT, so that the

     function can check that there is sufficient space. Note, that

     overlapping buffers are not allowed.



     Depending on the selected algorithms and encryption mode, the

     length of the buffers must be a multiple of the block size.



     The function returns `0' on success or an error code.



   OpenPGP (as defined in RFC-2440) requires a special sync operation in

some places, the following function is used for this:



 -- Function: gcry_error_t gcry_cipher_sync (gcry_cipher_hd_t H)

     Perform the OpenPGP sync operation on context H. Note, that this

     is a no-op unless the context was created with the flag

     `GCRY_CIPHER_ENABLE_SYNC'



   Some of the described functions are implemented as macros utilizing a

catch-all control function.  This control function is rarely used

directly but there is nothing which would inhibit it:



 -- Function: gcry_error_t gcry_cipher_ctl (gcry_cipher_hd_t H, int

          CMD, void *BUFFER, size_t BUFLEN)

     `gcry_cipher_ctl' controls various aspects of the cipher module and

     specific cipher contexts.  Usually some more specialized functions

     or macros are used for this purpose.  The semantics of the

     function and its parameters depends on the the command CMD and the

     passed context handle H.  Please see the comments in the source

     code (`src/global.c') for details.



 -- Function: gcry_error_t gcry_cipher_info (gcry_cipher_hd_t H, int

          WHAT, void *BUFFER, size_t *NBYTES)

     `gcry_cipher_info' is used to retrieve various information about a

     cipher context or the cipher module in general.



     Currently no information is available.





File: gcrypt.info,  Node: General cipher functions,  Prev: Working with cipher handles,  Up: Symmetric cryptography



5.5 General cipher functions

============================



To work with the algorithms, several functions are available to map

algorithm names to the internal identifiers, as well as ways to

retrieve information about an algorithm or the current cipher context.



 -- Function: gcry_error_t gcry_cipher_algo_info (int ALGO, int WHAT,

          void *BUFFER, size_t *NBYTES)

     This function is used to retrieve information on a specific

     algorithm.  You pass the cipher algorithm ID as ALGO and the type

     of information requested as WHAT. The result is either returned as

     the return code of the function or copied to the provided BUFFER

     whose allocated length must be available in an integer variable

     with the address passed in NBYTES.  This variable will also

     receive the actual used length of the buffer.



     Here is a list of supported codes for WHAT:



    `GCRYCTL_GET_KEYLEN:'

          Return the length of the key. If the algorithm supports

          multiple key lengths, the maximum supported value is

          returned.  The length is returned as number of octets (bytes)

          and not as number of bits in NBYTES; BUFFER must be zero.



    `GCRYCTL_GET_BLKLEN:'

          Return the block length of the algorithm.  The length is

          returned as a number of octets in NBYTES; BUFFER must be zero.



    `GCRYCTL_TEST_ALGO:'

          Returns `0' when the specified algorithm is available for use.

          BUFFER and NBYTES must be zero.







 -- Function: const char *gcry_cipher_algo_name (int ALGO)

     `gcry_cipher_algo_name' returns a string with the name of the

     cipher algorithm ALGO.  If the algorithm is not known or another

     error occurred, an empty string is returned.  This function will

     never return `NULL'.



 -- Function: int gcry_cipher_map_name (const char *NAME)

     `gcry_cipher_map_name' returns the algorithm identifier for the

     cipher algorithm described by the string NAME.  If this algorithm

     is not available `0' is returned.



 -- Function: int gcry_cipher_mode_from_oid (const char *STRING)

     Return the cipher mode associated with an ASN.1 object identifier.

     The object identifier is expected to be in the IETF-style dotted

     decimal notation.  The function returns `0' for an unknown object

     identifier or when no mode is associated with it.





File: gcrypt.info,  Node: Hashing,  Next: Public Key cryptography (I),  Prev: Symmetric cryptography,  Up: Top



6 Hashing

*********



Libgcrypt provides an easy and consistent to use interface for hashing.

Hashing is buffered and several hash algorithms can be updated at

once.  It is possible to calculate a MAC using the same routines.  The

programming model follows an open/process/close paradigm and is in that

similar to other building blocks provided by Libgcrypt.



   For convenience reasons, a few cyclic redundancy check value

operations are also supported.



* Menu:



* Available hash algorithms::   List of hash algorithms supported by the library.

* Hash algorithm modules::      How to work with hash algorithm modules.

* Working with hash algorithms::  List of functions related to hashing.





File: gcrypt.info,  Node: Available hash algorithms,  Next: Hash algorithm modules,  Up: Hashing



6.1 Available hash algorithms

=============================



`GCRY_MD_NONE'

     This is not a real algorithm but used by some functions as an error

     return value.  This constant is guaranteed to have the value `0'.



`GCRY_MD_SHA1'

     This is the SHA-1 algorithm which yields a message digest of 20

     bytes.



`GCRY_MD_RMD160'

     This is the 160 bit version of the RIPE message digest

     (RIPE-MD-160).  Like SHA-1 it also yields a digest of 20 bytes.



`GCRY_MD_MD5'

     This is the well known MD5 algorithm, which yields a message

     digest of 16 bytes.



`GCRY_MD_MD4'

     This is the MD4 algorithm, which yields a message digest of 16

     bytes.



`GCRY_MD_MD2'

     This is an reserved identifier for MD-2; there is no

     implementation yet.



`GCRY_MD_TIGER'

     This is the TIGER/192 algorithm which yields a message digest of

     24 bytes.



`GCRY_MD_HAVAL'

     This is an reserved for the HAVAL algorithm with 5 passes and 160

     bit. It yields a message digest of 20 bytes.  Note that there is no

     implementation yet available.



`GCRY_MD_SHA256'

     This is the SHA-256 algorithm which yields a message digest of 32

     bytes.  See FIPS 180-2 for the specification.



`GCRY_MD_SHA384'

     This is reserved for SHA-2 with 384 bits. It yields a message

     digest of 48 bytes.  Note that there is no implementation yet

     available.



`GCRY_MD_SHA512'

     This is reserved for SHA-2 with 512 bits. It yields a message

     digest of 64 bytes.  Note that there is no implementation yet

     available.



`GCRY_MD_CRC32'

     This is the ISO 3309 and ITU-T V.42 cyclic redundancy check.  It

     yields an output of 4 bytes.



`GCRY_MD_CRC32_RFC1510'

     This is the above cyclic redundancy check function, as modified by

     RFC 1510.  It yields an output of 4 bytes.



`GCRY_MD_CRC24_RFC2440'

     This is the OpenPGP cyclic redundancy check function.  It yields an

     output of 3 bytes.







File: gcrypt.info,  Node: Hash algorithm modules,  Next: Working with hash algorithms,  Prev: Available hash algorithms,  Up: Hashing



6.2 Hash algorithm modules

==========================



Libgcrypt makes it possible to load additional `message digest

modules'; these cipher can be used just like the message digest

algorithms that are built into the library directly.  For an

introduction into extension modules, see *Note Modules::.



 -- Data type: gcry_md_spec_t

     This is the `module specification structure' needed for registering

     message digest modules, which has to be filled in by the user

     before it can be used to register a module.  It contains the

     following members:



    `const char *name'

          The primary name of this algorithm.



    `unsigned char *asnoid'

          Array of bytes that form the ASN OID.



    `int asnlen'

          Length of bytes in `asnoid'.



    `gcry_md_oid_spec_t *oids'

          A list of OIDs that are to be associated with the algorithm.

          The list's last element must have it's `oid' member set to

          NULL.  See below for an explanation of this type.  See below

          for an explanation of this type.



    `int mdlen'

          Length of the message digest algorithm.  See below for an

          explanation of this type.



    `gcry_md_init_t init'

          The function responsible for initializing a handle.  See

          below for an explanation of this type.



    `gcry_md_write_t write'

          The function responsible for writing data into a message

          digest context.  See below for an explanation of this type.



    `gcry_md_final_t final'

          The function responsible for `finalizing' a message digest

          context.  See below for an explanation of this type.



    `gcry_md_read_t read'

          The function responsible for reading out a message digest

          result.  See below for an explanation of this type.



    `size_t contextsize'

          The size of the algorithm-specific `context', that should be

          allocated for each handle.



 -- Data type: gcry_md_oid_spec_t

     This type is used for associating a user-provided algorithm

     implementation with certain OIDs.  It contains the following

     members:



    `const char *oidstring'

          Textual representation of the OID.



 -- Data type: gcry_md_init_t

     Type for the `init' function, defined as: void (*gcry_md_init_t)

     (void *c)



 -- Data type: gcry_md_write_t

     Type for the `write' function, defined as: void (*gcry_md_write_t)

     (void *c, unsigned char *buf, size_t nbytes)



 -- Data type: gcry_md_final_t

     Type for the `final' function, defined as: void (*gcry_md_final_t)

     (void *c)



 -- Data type: gcry_md_read_t

     Type for the `read' function, defined as: unsigned char

     *(*gcry_md_read_t) (void *c)



 -- Function: gcry_error_t gcry_md_register (gcry_md_spec_t *DIGEST,

          unsigned int *algorithm_id, gcry_module_t *MODULE)

     Register a new digest module whose specification can be found in

     DIGEST.  On success, a new algorithm ID is stored in ALGORITHM_ID

     and a pointer representing this module is stored in MODULE.



 -- Function: void gcry_md_unregister (gcry_module_t MODULE)

     Unregister the digest identified by MODULE, which must have been

     registered with gcry_md_register.



 -- Function: gcry_error_t gcry_md_list (int *LIST, int *LIST_LENGTH)

     Get a list consisting of the IDs of the loaded message digest

     modules.  If LIST is zero, write the number of loaded message

     digest modules to LIST_LENGTH and return.  If LIST is non-zero,

     the first *LIST_LENGTH algorithm IDs are stored in LIST, which

     must be of according size.  In case there are less message digests

     modules than *LIST_LENGTH, *LIST_LENGTH is updated to the correct

     number.





File: gcrypt.info,  Node: Working with hash algorithms,  Prev: Hash algorithm modules,  Up: Hashing



6.3 Working with hash algorithms

================================



To use most of these function it is necessary to create a context; this

is done using:



 -- Function: gcry_error_t gcry_md_open (gcry_md_hd_t *HD, int ALGO,

          unsigned int FLAGS)

     Create a message digest object for algorithm ALGO.  FLAGS may be

     given as an bitwise OR of constants described below.  ALGO may be

     given as `0' if the algorithms to use are later set using

     `gcry_md_enable'. HD is guaranteed to either receive a valid

     handle or NULL.



     For a list of supported algorithms, see *Note Available hash

     algorithms::.



     The flags allowed for MODE are:



    `GCRY_MD_FLAG_SECURE'

          Allocate all buffers and the resulting digest in "secure

          memory".  Use this is the hashed data is highly confidential.



    `GCRY_MD_FLAG_HMAC'

          Turn the algorithm into a HMAC message authentication

          algorithm.  This does only work if just one algorithm is

          enabled for the handle and SHA-384 and SHA512 is not used.

          Note that the function `gcry_md_setkey' must be used set the

          MAC key.  If you want CBC message authentication codes based

          on a cipher, see *Note Working with cipher handles::.





     You may use the function `gcry_md_is_enabled' to later check

     whether an algorithm has been enabled.





   If you want to calculate several hash algorithms at the same time,

you have to use the following function right after the `gcry_md_open':



 -- Function: gcry_error_t gcry_md_enable (gcry_md_hd_t H, int ALGO)

     Add the message digest algorithm ALGO to the digest object

     described by handle H.  Duplicated enabling of algorithms is

     detected and ignored.



   If the flag `GCRY_MD_FLAG_HMAC' was used, the key for the MAC must

be set using the function:



 -- Function: gcry_error_t gcry_md_setkey (gcry_md_hd_t H, const void

          *KEY, size_t KEYLEN)

     For use with the HMAC feature, set the MAC key to the value of KEY

     of length KEYLEN.



   After you are done with the hash calculation, you should release the

resources by using:



 -- Function: void gcry_md_close (gcry_md_hd_t H)

     Release all resources of hash context H.  H should not be used

     after a call to this function.  A `NULL' passed as H is ignored.





   Often you have to do several hash operations using the same

algorithm.  To avoid the overhead of creating and releasing context, a

reset function is provided:



 -- Function: void gcry_md_reset (gcry_md_hd_t H)

     Reset the current context to its initial state.  This is

     effectively identical to a close followed by an open and enabling

     all currently active algorithms.



   Often it is necessary to start hashing some data and than continue to

hash different data.  To avoid hashing the same data several times

(which might not even be possible if the data is received from a pipe),

a snapshot of the current hash context can be taken and turned into a

new context:



 -- Function: gcry_error_t gcry_md_copy (gcry_md_hd_t *HANDLE_DST,

          gcry_md_hd_t HANDLE_SRC)

     Create a new digest object as an exact copy of the object

     described by handle HANDLE_SRC and store it in HANDLE_DST.  The

     context is not reset and you can continue to hash data using this

     context and independently using the original context.



   Now that we have prepared everything to calculate hashes, its time to

see how it is actually done.  There are 2  ways for this, one to update

the hash with a block of memory and one macro to update the hash by

just one character.  Both may be used intermixed.



 -- Function: void gcry_md_write (gcry_md_hd_t H, const void *BUFFER,

          size_t LENGTH)

     Pass LENGTH bytes of the data in BUFFER to the digest object with

     handle H to update the digest values. This function should be used

     for large blocks of data.



 -- Function: void gcry_md_putc (gcry_md_hd_t H, int C)

     Pass the byte in C to the digest object with handle H to update

     the digest value.  This is an efficient function, implemented as a

     macro to buffer the data before an actual update.



   The semantics of the hash functions don't allow to read out

intermediate message digests because the calculation must be finalized

fist.  This finalization may for example include the number of bytes

hashed in the message digest.



 -- Function: void gcry_md_final (gcry_md_hd_t H)

     Finalize the message digest calculation.  This is not really needed

     because `gcry_md_read' does this implicitly.  After this has been

     done no further updates (by means of `gcry_md_write' or

     `gcry_md_putc' are allowed.  Only the first call to this function

     has an effect. It is implemented as a macro.



   The way to read out the calculated message digest is by using the

function:



 -- Function: unsigned char *gcry_md_read (gcry_md_hd_t H, int ALGO)

     `gcry_md_read' returns the message digest after finalizing the

     calculation.  This function may be used as often as required but

     it will always return the same value for one handle.  The returned

     message digest is allocated within the message context and

     therefore valid until the handle is released or reseted (using

     `gcry_md_close' or `gcry_md_reset'.  ALGO may be given as 0 to

     return the only enabled message digest or it may specify one of

     the enabled algorithms.  The function does return `NULL' if the

     requested algorithm has not been enabled.



   Because it is often necessary to get the message digest of one block

of memory, a fast convenience function is available for this task:



 -- Function: void gcry_md_hash_buffer (int ALGO, void *DIGEST, const

          cvoid *BUFFER, size_t LENGTH);

     `gcry_md_hash_buffer' is a shortcut function to calculate a message

     digest of a buffer.  This function does not require a context and

     immediately returns the message digest of the LENGTH bytes at

     BUFFER.  DIGEST must be allocated by the caller, large enough to

     hold the message digest yielded by the the specified algorithm

     ALGO.  This required size may be obtained by using the function

     `gcry_md_get_algo_dlen'.



     Note, that this function will abort the process if an unavailable

     algorithm is used.



   Hash algorithms are identified by internal algorithm numbers (see

`gcry_md_open' for a list.  However, in most applications they are used

by names, so 2 functions are available to map between string

representations and hash algorithm identifiers.



 -- Function: const char *gcry_md_algo_name (int ALGO)

     Map the digest algorithm id ALGO to a string representation of the

     algorithm name.  For unknown algorithms this functions returns an

     empty string.  This function should not be used to test for the

     availability of an algorithm.



 -- Function: int gcry_md_map_name (const char *NAME)

     Map the algorithm with NAME to a digest algorithm identifier.

     Returns 0 if the algorithm name is not known.  Names representing

     ASN.1 object identifiers are recognized if the IETF dotted format

     is used and the OID is prefixed with either "`oid.'" or "`OID.'".

     For a list of supported OIDs, see the source code at

     `cipher/md.c'. This function should not be used to test for the

     availability of an algorithm.



 -- Function: gcry_error_t gcry_md_get_asnoid (int ALGO, void *BUFFER,

          size_t *LENGTH)

     Return an DER encoded ASN.1 OID for the algorithm ALGO in the user

     allocated BUFFER. LENGTH must point to variable with the available

     size of BUFFER and receives after return the actual size of the

     returned OID.  The returned error code may be `GPG_ERR_TOO_SHORT'

     if the provided buffer is to short to receive the OID; it is

     possible to call the function with `NULL' for BUFFER to have it

     only return the required size.  The function returns 0 on success.





   To test whether an algorithm is actually available for use, the

following macro should be used:



 -- Function: gcry_error_t gcry_md_test_algo (int ALGO)

     The macro returns 0 if the algorithm ALGO is available for use.



   If the length of a message digest is not known, it can be retrieved

using the following function:



 -- Function: unsigned int gcry_md_get_algo_dlen (int ALGO)

     Retrieve the length in bytes of the digest yielded by algorithm

     ALGO.  This is often used prior to `gcry_md_read' to allocate

     sufficient memory for the digest.



   In some situations it might be hard to remember the algorithm used

for the ongoing hashing. The following function might be used to get

that information:



 -- Function: int gcry_md_get_algo (gcry_md_hd_t H)

     Retrieve the algorithm used with the handle H. Note, that this

     does not work reliable if more than one algorithm is enabled in H.



   The following macro might also be useful:



 -- Function: int gcry_md_is_secure (gcry_md_hd_t H)

     This function returns true when the digest object H is allocated

     in "secure memory"; i.e. H was created with the

     `GCRY_MD_FLAG_SECURE'.



 -- Function: int gcry_md_is_enabled (gcry_md_hd_t H, int ALGO)

     This function returns true when the algorithm ALGO has been

     enabled for the digest object H.



   Tracking bugs related to hashing is often a cumbersome task which

requires to add a lot of printf statements into the code.  Libgcrypt

provides an easy way to avoid this.  The actual data hashed can be

written to files on request.  The following 2 macros should be used to

implement such a debugging facility:



 -- Function: void gcry_md_start_debug (gcry_md_hd_t H, const char

          *SUFFIX)

     Enable debugging for the digest object with handle H.  This

     creates create files named `dbgmd-<n>.<string>' while doing the

     actual hashing.  SUFFIX is the string part in the filename.  The

     number is a counter incremented for each new hashing.  The data in

     the file is the raw data as passed to `gcry_md_write' or

     `gcry_md_putc'.



 -- Function: void gcry_md_stop_debug (gcry_md_hd_t H, int RESERVED)

     Stop debugging on handle H.  RESERVED should be specified as 0.

     This function is usually not required because `gcry_md_close' does

     implicitly stop debugging.





File: gcrypt.info,  Node: Public Key cryptography (I),  Next: Public Key cryptography (II),  Prev: Hashing,  Up: Top



7 Public Key cryptography (I)

*****************************



Public key cryptography, also known as asymmetric cryptography, is an

easy way for key management and to provide digital signatures.

Libgcrypt provides two completely different interfaces to public key

cryptography, this chapter explains the one based on S-expressions.



* Menu:



* Available algorithms::        Algorithms supported by the library.

* Used S-expressions::          Introduction into the used S-expression.

* Public key modules::          How to work with public key modules.

* Cryptographic Functions::     Functions for performing the cryptographic actions.

* General public-key related Functions::  General functions, not implementing any cryptography.





File: gcrypt.info,  Node: Available algorithms,  Next: Used S-expressions,  Up: Public Key cryptography (I)



7.1 Available algorithms

========================



Libgcrypt supports the RSA (Rivest-Shamir-Adleman) algorithms as well

as DSA (Digital Signature Algorithm) and ElGamal.  The versatile

interface allows to add more algorithms in the future.





File: gcrypt.info,  Node: Used S-expressions,  Next: Public key modules,  Prev: Available algorithms,  Up: Public Key cryptography (I)



7.2 Used S-expressions

======================



Libgcrypt's API for asymmetric cryptography is based on data structures

called S-expressions (see XXXX) and does not work with contexts as most

of the other building blocks of Libgcrypt do.



   The following information are stored in S-expressions:



keys



plain text data



encrypted data



signatures



To describe how Libgcrypt expect keys, we use some examples. Note that

words in uppercase indicate parameters whereas lowercase words are

literals.



     (private-key

       (dsa

         (p P-MPI)

         (q Q-MPI)

         (g G-MPI)

         (y Y-MPI)

         (x X-MPI)))



This specifies a DSA private key with the following parameters:



P-MPI

     DSA prime p.



Q-MPI

     DSA group order q (which is a prime divisor of p-1).



G-MPI

     DSA group generator g.



Y-MPI

     DSA public key value y = g^x \bmod p.



X-MPI

     DSA secret exponent x.



   All the MPI values are  expected to be in `GCRYMPI_FMT_USG' format.

The public key is similar with "private-key" replaced by "public-key"

and no X-MPI.



   An easy way to create such an S-expressions is by using

`gcry_sexp_build' which allows to pass a string with printf-like

escapes to insert MPI values.



Here is an example for an RSA key:



     (private-key

       (rsa

         (n N-MPI)

         (e E-MPI)

         (d D-MPI)

         (p P-MPI)

         (q Q-MPI)

         (u U-MPI)



with



N-MPI

     RSA public modulus n.



E-MPI

     RSA public exponent e.



D-MPI

     RSA secret exponent d = e^-1 \bmod (p-1)(q-1).



P-MPI

     RSA secret prime p.



Q-MPI

     RSA secret prime q with q > p.



U-MPI

     multiplicative inverse u = p^-1 \bmod q.





File: gcrypt.info,  Node: Public key modules,  Next: Cryptographic Functions,  Prev: Used S-expressions,  Up: Public Key cryptography (I)



7.3 Public key modules

======================



Libgcrypt makes it possible to load additional `public key modules';

these public key algorithms can be used just like the algorithms that

are built into the library directly.  For an introduction into

extension modules, see *Note Modules::.



 -- Data type: gcry_pk_spec_t

     This is the `module specification structure' needed for registering

     public key modules, which has to be filled in by the user before it

     can be used to register a module.  It contains the following

     members:



    `const char *name'

          The primary name of this algorithm.



    `char **aliases'

          A list of strings that are `aliases' for the algorithm.  The

          list must be terminated with a NULL element.



    `const char *elements_pkey'

          String containing the one-letter names of the MPI values

          contained in a public key.



    `const char *element_skey'

          String containing the one-letter names of the MPI values

          contained in a secret key.



    `const char *elements_enc'

          String containing the one-letter names of the MPI values that

          are the result of an encryption operation using this

          algorithm.



    `const char *elements_sig'

          String containing the one-letter names of the MPI values that

          are the result of a sign operation using this algorithm.



    `const char *elements_grip'

          String containing the one-letter names of the MPI values that

          are to be included in the `key grip'.



    `int use'

          The bitwise-OR of the following flags, depending on the

          abilities of the algorithm:

         `GCRY_PK_USAGE_SIGN'

               The algorithm supports signing and verifying of data.



         `GCRY_PK_USAGE_ENCR'

               The algorithm supports the encryption and decryption of

               data.



    `gcry_pk_generate_t generate'

          The function responsible for generating a new key pair.  See

          below for a description of this type.



    `gcry_pk_check_secret_key_t check_secret_key'

          The function responsible for checking the sanity of a

          provided secret key.  See below for a description of this

          type.



    `gcry_pk_encrypt_t encrypt'

          The function responsible for encrypting data.  See below for a

          description of this type.



    `gcry_pk_decrypt_t decrypt'

          The function responsible for decrypting data.  See below for a

          description of this type.



    `gcry_pk_sign_t sign'

          The function responsible for signing data.  See below for a

          description of this type.



    `gcry_pk_verify_t verify'

          The function responsible for verifying that the provided

          signature matches the provided data.  See below for a

          description of this type.



    `gcry_pk_get_nbits_t get_nbits'

          The function responsible for returning the number of bits of

          a provided key.  See below for a description of this type.



 -- Data type: gcry_pk_generate_t

     Type for the `generate' function, defined as: gcry_err_code_t

     (*gcry_pk_generate_t) (int algo, unsigned int nbits, unsigned long

     use_e, gcry_mpi_t *skey, gcry_mpi_t **retfactors)



 -- Data type: gcry_pk_check_secret_key_t

     Type for the `check_secret_key' function, defined as:

     gcry_err_code_t (*gcry_pk_check_secret_key_t) (int algo,

     gcry_mpi_t *skey)



 -- Data type: gcry_pk_encrypt_t

     Type for the `encrypt' function, defined as: gcry_err_code_t

     (*gcry_pk_encrypt_t) (int algo, gcry_mpi_t *resarr, gcry_mpi_t

     data, gcry_mpi_t *pkey, int flags)



 -- Data type: gcry_pk_decrypt_t

     Type for the `decrypt' function, defined as: gcry_err_code_t

     (*gcry_pk_decrypt_t) (int algo, gcry_mpi_t *result, gcry_mpi_t

     *data, gcry_mpi_t *skey, int flags)



 -- Data type: gcry_pk_sign_t

     Type for the `sign' function, defined as: gcry_err_code_t

     (*gcry_pk_sign_t) (int algo, gcry_mpi_t *resarr, gcry_mpi_t data,

     gcry_mpi_t *skey)



 -- Data type: gcry_pk_verify_t

     Type for the `verify' function, defined as: gcry_err_code_t

     (*gcry_pk_verify_t) (int algo, gcry_mpi_t hash, gcry_mpi_t *data,

     gcry_mpi_t *pkey, int (*cmp) (void *, gcry_mpi_t), void *opaquev)



 -- Data type: gcry_pk_get_nbits_t

     Type for the `get_nbits' function, defined as: unsigned

     (*gcry_pk_get_nbits_t) (int algo, gcry_mpi_t *pkey)



 -- Function: gcry_error_t gcry_pk_register (gcry_pk_spec_t *PUBKEY,

          unsigned int *algorithm_id, gcry_module_t *MODULE)

     Register a new public key module whose specification can be found

     in PUBKEY.  On success, a new algorithm ID is stored in

     ALGORITHM_ID and a pointer representing this module is stored in

     MODULE.



 -- Function: void gcry_pk_unregister (gcry_module_t MODULE)

     Unregister the public key module identified by MODULE, which must

     have been registered with gcry_pk_register.



 -- Function: gcry_error_t gcry_pk_list (int *LIST, int *LIST_LENGTH)

     Get a list consisting of the IDs of the loaded pubkey modules.  If

     LIST is zero, write the number of loaded pubkey modules to

     LIST_LENGTH and return.  If LIST is non-zero, the first

     *LIST_LENGTH algorithm IDs are stored in LIST, which must be of

     according size.  In case there are less pubkey modules than

     *LIST_LENGTH, *LIST_LENGTH is updated to the correct number.





File: gcrypt.info,  Node: Cryptographic Functions,  Next: General public-key related Functions,  Prev: Public key modules,  Up: Public Key cryptography (I)



7.4 Cryptographic Functions

===========================



Note, that we will in future allow to use keys without p,q and u

specified and may also support other parameters for performance reasons.



Some functions operating on S-expressions support `flags', that

influence the operation.  These flags have to be listed in a

sub-S-expression named `flags'; the following flags are known:



PKCS1

     Use PKCS#1 block type 2 padding.



NO-BLINDING

     Do not use a technique called `blinding', which is used by default

     in order to prevent leaking of secret information.  Blinding is

     only implemented by RSA, but it might be implemented by other

     algorithms in the future as well, when necessary.



Now that we know the key basics, we can carry on and explain how to

encrypt and decrypt data.  In almost all cases the data is a random

session key which is in turn used for the actual encryption of the real

data.  There are 2 functions to do this:



 -- Function: gcry_error_t gcry_pk_encrypt (gcry_sexp_t *R_CIPH,

          gcry_sexp_t DATA, gcry_sexp_t PKEY)

     Obviously a public key must be provided for encryption.  It is

     expected as an appropriate S-expression (see above) in PKEY.  The

     data to be encrypted can either be in the simple old format, which

     is a very simple S-expression consisting only of one MPI, or it

     may be a more complex S-expression which also allows to specify

     flags for operation, like e.g. padding rules.



     If you don't want to let Libgcrypt handle the padding, you must

     pass an appropriate MPI using this expression for DATA:



          (data

            (flags raw)

            (value MPI))



     This has the same semantics as the old style MPI only way.  MPI is

     the actual data, already padded appropriate for your protocol.

     Most systems however use PKCS#1 padding and so you can use this

     S-expression for DATA:



          (data

            (flags pkcs1)

            (value BLOCK))



     Here, the "flags" list has the "pkcs1" flag which let the function

     know that it should provide PKCS#1 block type 2 padding.  The

     actual data to be encrypted is passed as a string of octets in

     BLOCK.  The function checks that this data actually can be used

     with the given key, does the padding and encrypts it.



     If the function could successfully perform the encryption, the

     return value will be 0 and a a new S-expression with the encrypted

     result is allocated and assign to the variable at the address of

     R_CIPH.  The caller is responsible to release this value using

     `gcry_sexp_release'.  In case of an error, an error code is

     returned and R_CIPH will be set to `NULL'.



     The returned S-expression has this format when used with RSA:



          (enc-val

            (rsa

              (a A-MPI)))



     Where A-MPI is an MPI with the result of the RSA operation.  When

     using the ElGamal algorithm, the return value will have this

     format:



          (enc-val

            (elg

              (a A-MPI)

              (b B-MPI)))



     Where A-MPI and B-MPI are MPIs with the result of the ElGamal

     encryption operation.



 -- Function: gcry_error_t gcry_pk_decrypt (gcry_sexp_t *R_PLAIN,

          gcry_sexp_t DATA, gcry_sexp_t SKEY)

     Obviously a private key must be provided for decryption.  It is

     expected as an appropriate S-expression (see above) in SKEY.  The

     data to be decrypted must match the format of the result as

     returned by `gcry_pk_encrypt', but should be enlarged with a

     `flags' element:



          (enc-val

            (flags)

            (elg

              (a A-MPI)

              (b B-MPI)))



     Note, that this function currently does not know of any padding

     methods and the caller must do any un-padding on his own.



     The function returns 0 on success or an error code.  The variable

     at the address of R_PLAIN will be set to NULL on error or receive

     the decrypted value on success.  The format of R_PLAIN is a simple

     S-expression part (i.e. not a valid one) with just one MPI if

     there was no `flags' element in DATA; if at least an empty `flags'

     is passed in DATA, the format is:



          (value PLAINTEXT)



   Another operation commonly performed using public key cryptography is

signing data.  In some sense this is even more important than

encryption because digital signatures are an important instrument for

key management.  Libgcrypt supports digital signatures using 2

functions, similar to the encryption functions:



 -- Function: gcry_error_t gcry_pk_sign (gcry_sexp_t *R_SIG,

          gcry_sexp_t DATA, gcry_sexp_t SKEY)

     This function creates a digital signature for DATA using the

     private key SKEY and place it into the variable at the address of

     R_SIG.  DATA may either be the simple old style S-expression with

     just one MPI or a modern and more versatile S-expression which

     allows to let Libgcrypt handle padding:



           (data

            (flags pkcs1)

            (hash HASH-ALGO BLOCK))



     This example requests to sign the data in BLOCK after applying

     PKCS#1 block type 1 style padding.  HASH-ALGO is a string with the

     hash algorithm to be encoded into the signature, this may be any

     hash algorithm name as supported by Libgcrypt.  Most likely, this

     will be "sha1", "rmd160" or "md5".  It is obvious that the length

     of BLOCK must match the size of that message digests; the function

     checks that this and other constraints are valid.



     If PKCS#1 padding is not required (because the caller does already

     provide a padded value), either the old format or better the

     following format should be used:



          (data

            (flags raw)

            (value MPI))



     Here, the data to be signed is directly given as an MPI.



     The signature is returned as a newly allocated S-expression in

     R_SIG using this format for RSA:



          (sig-val

            (rsa

              (s S-MPI)))



     Where S-MPI is the result of the RSA sign operation.  For DSA the

     S-expression returned is:



          (sig-val

            (dsa

              (r R-MPI)

              (s S-MPI)))



     Where R-MPI and S-MPI are the result of the DSA sign operation.

     For ElGamal signing (which is slow, yields large numbers and

     probably is not as secure as the other algorithms), the same

     format is used with "elg" replacing "dsa".



The operation most commonly used is definitely the verification of a

signature.  Libgcrypt provides this function:



 -- Function: gcry_error_t gcry_pk_verify (gcry_sexp_t SIG,

          gcry_sexp_t DATA, gcry_sexp_t PKEY)

     This is used to check whether the signature SIG matches the DATA.

     The public key PKEY must be provided to perform this verification.

     This function is similar in its parameters to `gcry_pk_sign' with

     the exceptions that the public key is used instead of the private

     key and that no signature is created but a signature, in a format

     as created by `gcry_pk_sign', is passed to the function in SIG.



     The result is 0 for success (i.e. the data matches the signature),

     or an error code where the most relevant code is

     `GCRYERR_BAD_SIGNATURE' to indicate that the signature does not

     match the provided data.







File: gcrypt.info,  Node: General public-key related Functions,  Prev: Cryptographic Functions,  Up: Public Key cryptography (I)



7.5 General public-key related Functions

========================================



A couple of utility functions are available to retrieve the length of

the key, map algorithm identifiers and perform sanity checks:



 -- Function: const char * gcry_pk_algo_name (int ALGO)

     Map the public key algorithm id ALGO to a string representation of

     the algorithm name.  For unknown algorithms this functions returns

     an empty string.



 -- Function: int gcry_pk_map_name (const char *NAME)

     Map the algorithm NAME to a public key algorithm Id.  Returns 0 if

     the algorithm name is not known.



 -- Function: int gcry_pk_test_algo (int ALGO)

     Return 0 if the public key algorithm ALGO is available for use.

     Note, that this is implemented as a macro.



 -- Function: unsigned int gcry_pk_get_nbits (gcry_sexp_t KEY)

     Return what is commonly referred as the key length for the given

     public or private in KEY.



 -- Function: unsigned char * gcry_pk_get_keygrip (gcry_sexp_t KEY,

          unsigned char *ARRAY)

     Return the so called "keygrip" which is the SHA-1 hash of the

     public key parameters expressed in a way depended on the

     algorithm.  ARRAY must either provide space for 20 bytes or

     `NULL;'. In the latter case a newly allocated array of that size

     is returned.  On success a pointer to the newly allocated space or

     to ARRAY is returned.  `NULL' is returned to indicate an error

     which is most likely an unknown algorithm or one where a "keygrip"

     has not yet been defined.  The function accepts public or secret

     keys in KEY.



 -- Function: gcry_error_t gcry_pk_testkey (gcry_sexp_t KEY)

     Return zero if the private key KEY is `sane', an error code

     otherwise.  Note, that it is not possible to chek the `saneness'

     of a public key.





 -- Function: int gcry_pk_algo_info (int ALGO, int WHAT, void *BUFFER,

          size_t *NBYTES)

     Depending on the value of WHAT return various information about

     the public key algorithm with the id ALGO.  Note, that the

     function returns `-1' on error and the actual error code must be

     retrieved using the function `gcry_errno'.  The currently defined

     values for WHAT are:



    `GCRYCTL_TEST_ALGO:'

          Return 0 when the specified algorithm is available for use.

          BUFFER must be `NULL', NBYTES may be passed as `NULL' or

          point to a variable with the required usage of the algorithm.

          This may be 0 for "don't care" or the bit-wise OR of these

          flags:



         `GCRY_PK_USAGE_SIGN'

               Algorithm is usable for signing.



         `GCRY_PK_USAGE_ENCR'

               Algorithm is usable for encryption.



    `GCRYCTL_GET_ALGO_USAGE:'

          Return the usage flags for the given algorithm.  An invalid

          algorithm return 0.  Disabled algorithms are ignored here

          because we want to know whether the algorithm is at all

          capable of a certain usage.



    `GCRYCTL_GET_ALGO_NPKEY'

          Return the number of elements the public key for algorithm

          ALGO consist of.  Return 0 for an unknown algorithm.



    `GCRYCTL_GET_ALGO_NSKEY'

          Return the number of elements the private key for algorithm

          ALGO consist of.  Note that this value is always larger than

          that of the public key.  Return 0 for an unknown algorithm.



    `GCRYCTL_GET_ALGO_NSIGN'

          Return the number of elements a signature created with the

          algorithm ALGO consists of.  Return 0 for an unknown

          algorithm or for an algorithm not capable of creating

          signatures.



    `GCRYCTL_GET_ALGO_NENC'

          Return the number of elements a encrypted message created

          with the algorithm ALGO consists of.  Return 0 for an unknown

          algorithm or for an algorithm not capable of encryption.



     Please note that parameters not required should be passed as

     `NULL'.



 -- Function: gcry_error_t gcry_pk_ctl (int CMD, void *BUFFER,

          size_t BUFLEN)

     This is a general purpose function to perform certain control

     operations.  CMD controls what is to be done. The return value is

     0 for success or an error code.  Currently supported values for

     CMD are:



    `GCRYCTL_DISABLE_ALGO'

          Disable the algorithm given as an algorithm id in BUFFER.

          BUFFER must point to an `int' variable with the algorithm id

          and BUFLEN must have the value `sizeof (int)'.





Libgcrypt also provides a function for generating public key pairs:



 -- Function: gcry_error_t gcry_pk_genkey (gcry_sexp_t *R_KEY,

          gcry_sexp_t PARMS)

     This function create a new public key pair using information given

     in the S-expression PARMS and stores the private and the public key

     in one new S-expression at the address given by R_KEY.  In case of

     an error, R_KEY is set to `NULL'.  The return code is 0 for

     success or an error code otherwise.



     Here is an example for PARMS for creating a 1024 bit RSA key:



          (genkey

            (rsa

              (nbits 4:1024)))



     To create an ElGamal key, substitute "elg" for "rsa" and to create

     a DSA key use "dsa".  Valid ranges for the key length depend on the

     algorithms; all commonly used key lengths are supported.  Currently

     supported parameters are:



    `nbits'

          This is always required to specify the length of the key.

          The argument is a string with a number in C-notation.



    `rsa-use-e'

          This is only used with RSA to give a hint for the public

          exponent. The value will be used as a base to test for a

          usable exponent. Some values are special:



         `0'

               Use a secure and fast value.  This is currently the

               number 41.



         `1'

               Use a secure value as required by some specification.

               This is currently the number 65537.



         `2'

               Reserved



          If this parameter is not used, Libgcrypt uses for historic

          reasons 65537.





     The key pair is returned in a format depending on the algorithm.

     Both private and public keys are returned in one container and may

     be accompanied by some miscellaneous information.



     As an example, here is what the ElGamal key generation returns:



          (key-data

            (public-key

              (elg

                (p P-MPI)

                (g G-MPI)

                (y Y-MPI)))

            (private-key

              (elg

                (p P-MPI)

                (g G-MPI)

                (y Y-MPI)

                (x X-MPI)))

            (misc-key-info

              (pm1-factors N1 N2 ... NN)))



     As you can see, some of the information is duplicated, but this

     provides an easy way to extract either the public or the private

     key.  Note that the order of the elements is not defined, e.g. the

     private key may be stored before the public key. N1 N2 ... NN is a

     list of prime numbers used to composite P-MPI; this is in general

     not a very useful information.





File: gcrypt.info,  Node: Public Key cryptography (II),  Next: Random Numbers,  Prev: Public Key cryptography (I),  Up: Top



8 Public Key cryptography (II)

******************************



This chapter documents the alternative interface to asymmetric

cryptography (ac) that is not based on S-expressions, but on native C

data structures.  As opposed to the pk interface described in the

former chapter, this one follows an open/use/close paradigm like other

building blocks of the library.



* Menu:



* Available asymmetric algorithms::  List of algorithms supported by the library.

* Working with sets of data::   How to work with sets of data.

* Working with handles::        How to use handles.

* Working with keys::           How to work with keys.

* Using cryptographic functions::  How to perform cryptographic operations.

* Handle-independent functions::  General functions independent of handles.





File: gcrypt.info,  Node: Available asymmetric algorithms,  Next: Working with sets of data,  Up: Public Key cryptography (II)



8.1 Available asymmetric algorithms

===================================



Libgcrypt supports the RSA (Rivest-Shamir-Adleman) algorithms as well

as DSA (Digital Signature Algorithm) and ElGamal.  The versatile

interface allows to add more algorithms in the future.



 -- Data type: gcry_ac_id_t

     The following constants are defined for this type:



    `GCRY_AC_RSA'

          Riven-Shamir-Adleman



    `GCRY_AC_DSA'

          Digital Signature Algorithm



    `GCRY_AC_ELG'

          ElGamal



    `GCRY_AC_ELG_E'

          ElGamal, encryption only.





File: gcrypt.info,  Node: Working with sets of data,  Next: Working with handles,  Prev: Available asymmetric algorithms,  Up: Public Key cryptography (II)



8.2 Working with sets of data

=============================



In the context of this interface the term `data set' refers to a list

of `named MPI values' that is used by functions performing

cryptographic operations.



   Such data sets are used for representing keys, since keys simply

consist of a variable amount of numbers.  Furthermore some functions

return data sets to the caller that are to be provided to other

functions.



   This section documents the data types, symbols and functions that are

relevant for working with such data sets.



 -- Data type: gcry_ac_data_t

     A data set, that is simply a list of named MPI values.



   The following flags are supported:



`GCRY_AC_FLAG_DEALLOC'

     Used for storing data in a data set.  If given, the data will be

     released by the library.



`GCRY_AC_FLAG_COPY'

     Used for storing/retrieving data in/from a data set.  If given, the

     library will create copies of the provided/contained data, which

     will then be given to the user/associated with the data set.



 -- Function: gcry_error_t gcry_ac_data_new (gcry_ac_data_t *DATA)

     Creates a new, empty data set and stores it in DATA.



 -- Function: void gcry_ac_data_destroy (gcry_ac_data_t DATA)

     Destroys the data set DATA.



 -- Function: gcry_error_t gcry_ac_data_set (gcry_ac_data_t DATA,

          unsigned int FLAGS, char *NAME, gcry_mpi_t MPI)

     Add the value MPI to DATA with the label NAME.  If FLAGS contains

     GCRY_AC_FLAG_DATA_COPY, the data set will contain copies of NAME

     and MPI.  If FLAGS contains GCRY_AC_FLAG_DATA_DEALLOC or

     GCRY_AC_FLAG_DATA_COPY, the values contained in the data set will

     be deallocated when they are to be removed from the data set.



 -- Function: gcry_error_t gcry_ac_data_copy (gcry_ac_data_t *DATA_CP,

          gcry_ac_data_t DATA)

     Create a copy of the data set DATA and store it in DATA_CP.



 -- Function: unsigned int gcry_ac_data_length (gcry_ac_data_t DATA)

     Returns the number of named MPI values inside of the data set DATA.



 -- Function: gcry_error_t gcry_ac_data_get_name (gcry_ac_data_t DATA,

          unsigned int FLAGS, char *NAME, gcry_mpi_t *MPI)

     Store the value labelled with NAME found in DATA in MPI.  If FLAGS

     contains GCRY_AC_FLAG_COPY, store a copy of the MPI value

     contained in the data set.  MPI may be NULL.



 -- Function: gcry_error_t gcry_ac_data_get_index (gcry_ac_data_t DATA,

          unsigned int flags, unsigned int INDEX, const char **NAME,

          gcry_mpi_t *MPI)

     Stores in NAME and MPI the named MPI value contained in the data

     set DATA with the index IDX.  If FLAGS contains GCRY_AC_FLAG_COPY,

     store copies of the values contained in the data set. NAME or MPI

     may be NULL.



 -- Function: void gcry_ac_data_clear (gcry_ac_data_t DATA)

     Destroys any values contained in the data set DATA.





File: gcrypt.info,  Node: Working with handles,  Next: Working with keys,  Prev: Working with sets of data,  Up: Public Key cryptography (II)



8.3 Working with handles

========================



In order to use an algorithm, an according handle must be created.

This is done using the following function:



 -- Function: gcry_error_t gcry_ac_open (gcry_ac_handle_t *HANDLE, int

          ALGORITHM, int FLAGS)

     Creates a new handle for the algorithm ALGORITHM and stores it in

     HANDLE.  FLAGS is not used yet.



     ALGORITHM must be a valid algorithm ID, see *Note Available

     algorithms::, for a list of supported algorithms and the according

     constants.  Besides using the listed constants directly, the

     functions `gcry_ac_name_to_id' may be used to convert the textual

     name of an algorithm into the according numeric ID.



 -- Function: void gcry_ac_close (gcry_ac_handle_t HANDLE)

     Destroys the handle HANDLE.





File: gcrypt.info,  Node: Working with keys,  Next: Using cryptographic functions,  Prev: Working with handles,  Up: Public Key cryptography (II)



8.4 Working with keys

=====================



 -- Data type: gcry_ac_key_type_t

     Defined constants:



    `GCRY_AC_KEY_TYPE_SECRET'

          Specifies a secret key.



    `GCRY_AC_KEY_TYPE_PUBLIC'

          Specifies a public key.



 -- Data type: gcry_ac_key_t

     This type represents a single `key', either a secret one or a

     public one.



 -- Data type: gcry_ac_key_pair_t

     This type represents a `key pair' containing a secret and a public

     key.



   Key data structures can be created in two different ways; a new key

pair can be generated, resulting in ready-to-use key.  Alternatively a

key can be initialized from a given data set.



 -- Function: gcry_error_t gcry_ac_key_init (gcry_ac_key_t *KEY,

          gcry_ac_handle_t HANDLE, gcry_ac_key_type_t TYPE,

          gcry_ac_data_t DATA)

     Creates a new key of type TYPE, consisting of the MPI values

     contained in the data set DATA and stores it in KEY.



 -- Function: gcry_error_t gcry_ac_key_pair_generate (gcry_ac_handle_t

          HANDLE, unsigned int NBITS, void *KEY_SPEC,

          gcry_ac_key_pair_t *KEY_PAIR, gcry_mpi_t **MISC_DATA)

     Generates a new key pair via the handle HANDLE of NBITS bits and

     stores it in KEY_PAIR.



     In case non-standard settings are wanted, a pointer to a structure

     of type `gcry_ac_key_spec_<algorithm>_t', matching the selected

     algorithm, can be given as KEY_SPEC.  MISC_DATA is not used yet.

     Such a structure does only exist for RSA.  A descriptions of the

     members of the supported structures follows.



    `gcry_ac_key_spec_rsa_t'



         `gcry_mpi_t e'

               Generate the key pair using a special `e'.  The value of

               `e' has the following meanings:

              `= 0'

                    Let Libgcrypt device what exponent should be used.



              `= 1'

                    Request the use of a "secure" exponent; this is

                    required by some specification to be 65537.



              `> 2'

                    Try starting at this value until a working exponent

                    is found.  Note, that the current implementation

                    leaks some information about the private key

                    because the incrementation used is not randomized.

                    Thus, this function will be changed in the future

                    to return a random exponent of the given size.



     Example code:

          {

            gcry_ac_key_pair_t key_pair;

            gcry_ac_key_spec_rsa  rsa_spec;



            rsa_spec.e = gcry_mpi_new (0);

            gcry_mpi_set_ui (rsa_spec.e, 1)



            err = gcry_ac_open  (&handle, GCRY_AC_RSA, 0);

            assert (! err);



            err = gcry_ac_key_pair_generate (handle, &key_pair, 1024, (void *) &rsa_spec);

            assert (! err);

          }



 -- Function: gcry_ac_key_t gcry_ac_key_pair_extract

          (gcry_ac_key_pair_t KEY_PAIR, gcry_ac_key_type_t WHICH)

     Returns the key of type WHICH out of the key pair KEY_PAIR.



 -- Function: void gcry_ac_key_destroy (gcry_ac_key_t KEY)

     Destroys the key KEY.



 -- Function: void gcry_ac_key_pair_destroy (gcry_ac_key_pair_t

          KEY_PAIR)

     Destroys the key pair KEY_PAIR.



 -- Function: gcry_ac_data_t gcry_ac_key_data_get (gcry_ac_key_t KEY)

     Returns the data set contained in the key KEY.



 -- Function: gcry_error_t gcry_ac_key_test (gcry_ac_handle_t HANDLE,

          gcry_ac_key_t KEY)

     Verifies that the private key KEY is sane via HANDLE.



 -- Function: gcry_error_t gcry_ac_key_get_nbits (gcry_ac_handle_t

          HANDLE, gcry_ac_key_t KEY, unsigned int *NBITS)

     Stores the number of bits of the key KEY in NBITS via HANDLE.



 -- Function: gcry_error_t gcry_ac_key_get_grip (gcry_ac_handle_t

          HANDLE, gcry_ac_key_t KEY, unsigned char *KEY_GRIP)

     Writes the 20 byte long key grip of the key KEY to KEY_GRIP via

     HANDLE.





File: gcrypt.info,  Node: Using cryptographic functions,  Next: Handle-independent functions,  Prev: Working with keys,  Up: Public Key cryptography (II)



8.5 Using cryptographic functions

=================================



The following flags might be relevant:



`GCRY_AC_FLAG_NO_BLINDING'

     Disable any blinding, which might be supported by the chosen

     algorithm; blinding is the default.



 -- Function: gcry_error_t gcry_ac_data_encrypt (gcry_ac_handle_t

          HANDLE, unsigned int FLAGS, gcry_ac_key_t KEY, gcry_mpi_t

          DATA_PLAIN, gcry_ac_data_t **DATA_ENCRYPTED)

     Encrypts the plain text MPI value DATA_PLAIN with the key public

     KEY under the control of the flags FLAGS and stores the resulting

     data set into DATA_ENCRYPTED.



 -- Function: gcry_error_t gcry_ac_data_decrypt (gcry_ac_handle_t

          HANDLE, unsigned int FLAGS, gcry_ac_key_t KEY, gcry_mpi_t

          *DATA_PLAIN, gcry_ac_data_t DATA_ENCRYPTED)

     Decrypts the encrypted data contained in the data set

     DATA_ENCRYPTED with the secret key KEY under the control of the

     flags FLAGS and stores the resulting plain text MPI value in

     DATA_PLAIN.



 -- Function: gcry_error_t gcry_ac_data_sign (gcry_ac_handle_t HANDLE,

          gcry_ac_key_t KEY, gcry_mpi_t DATA, gcry_ac_data_t

          *DATA_SIGNATURE)

     Signs the data contained in DATA with the secret key KEY and

     stores the resulting signature in the data set DATA_SIGNATURE.



 -- Function: gcry_error_t gcry_ac_data_verify (gcry_ac_handle_t

          HANDLE, gcry_ac_key_t KEY, gcry_mpi_t DATA, gcry_ac_data_t

          DATA_SIGNATURE)

     Verifies that the signature contained in the data set

     DATA_SIGNATURE is indeed the result of signing the data contained

     in DATA with the secret key belonging to the public key KEY.





File: gcrypt.info,  Node: Handle-independent functions,  Prev: Using cryptographic functions,  Up: Public Key cryptography (II)



8.6 Handle-independent functions

================================



 -- Function: gcry_error_t gcry_ac_id_to_name (gcry_ac_id_t ALGORITHM,

          const char **NAME)

     Stores the textual representation of the algorithm whose id is

     given in ALGORITHM in NAME.



 -- Function: gcry_error_t gcry_ac_name_to_id (const char *NAME,

          gcry_ac_id_t *ALGORITHM)

     Stores the numeric ID of the algorithm whose textual

     representation is contained in NAME in ALGORITHM.





File: gcrypt.info,  Node: Random Numbers,  Next: S-expressions,  Prev: Public Key cryptography (II),  Up: Top



9 Random Numbers

****************



* Menu:



* Quality of random numbers::   Libgcrypt uses different quality levels.

* Retrieving random numbers::   How to retrieve random numbers.





File: gcrypt.info,  Node: Quality of random numbers,  Next: Retrieving random numbers,  Up: Random Numbers



9.1 Quality of random numbers

=============================



Libgcypt offers random numbers of different quality levels:



 -- Data type: enum gcry_random_level

     The constants for the random quality levels are of this type.



`GCRY_WEAK_RANDOM'

     This should not anymore be used.  It has recently been changed to

     an alias of GCRY_STRONG_RANDOM.  Use `gcry_create_nonce' instead.



`GCRY_STRONG_RANDOM'

     Use this level for e.g. session keys and similar purposes.



`GCRY_VERY_STRONG_RANDOM'

     Use this level for e.g. key material.





File: gcrypt.info,  Node: Retrieving random numbers,  Prev: Quality of random numbers,  Up: Random Numbers



9.2 Retrieving random numbers

=============================



 -- Function: void gcry_randomize (unsigned char *BUFFER, size_t

          LENGTH, enum gcry_random_level LEVEL)

     Fill BUFFER with LENGTH random bytes using a random quality as

     defined by LEVEL.



 -- Function: void * gcry_random_bytes (size_t NBYTES, enum

          gcry_random_level LEVEL)

     Allocate a memory block consisting of NBYTES fresh random bytes

     using a random quality as defined by LEVEL.



 -- Function: void * gcry_random_bytes_secure (size_t NBYTES, enum

          gcry_random_level LEVEL)

     Allocate a memory block consisting of NBYTES fresh random bytes

     using a random quality as defined by LEVEL.  This function differs

     from `gcry_random_bytes' in that the returned buffer is allocated

     in a "secure" area of the memory.



 -- Function: void gcry_create_nonce (void *BUFFER, size_t LENGTH)

     Fill BUFFER with LENGTH unpredictable bytes.  This is commonly

     called a nonce and may also be used for initialization vectors and

     padding.  This is an extra function nearly independent of the

     other random function for 3 reasons: It better protects the

     regular random generator's internal state, provides better

     performance and does not drain the precious entropy pool.







File: gcrypt.info,  Node: S-expressions,  Next: MPI library,  Prev: Random Numbers,  Up: Top



10 S-expressions

****************



S-expressions are used by the public key functions to pass complex data

structures around.  These LISP like objects are used by some

cryptographic protocols (cf. RFC-2692) and Libgcrypt provides functions

to parse and construct them.  For detailed information, see `Ron

Rivest, code and description of S-expressions,

`http://theory.lcs.mit.edu/~rivest/sexp.html''.



* Menu:



* Data types for S-expressions::  Data types related with S-expressions.

* Working with S-expressions::  How to work with S-expressions.





File: gcrypt.info,  Node: Data types for S-expressions,  Next: Working with S-expressions,  Up: S-expressions



10.1 Data types for S-expressions

=================================



 -- Data type: gcry_sexp_t

     The `gcry_sexp_t' type describes an object with the Libgcrypt

     internal representation of an S-expression.





File: gcrypt.info,  Node: Working with S-expressions,  Prev: Data types for S-expressions,  Up: S-expressions



10.2 Working with S-expressions

===============================



There are several functions to create an Libgcrypt S-expression object

from its external representation or from a string template.  There is

also a function to convert the internal representation back into one of

the external formats:



 -- Function: gcry_error_t gcry_sexp_new (gcry_sexp_t *R_SEXP,

          const void *BUFFER, size_t LENGTH, int AUTODETECT)

     This is the generic function to create an new S-expression object

     from its external representation in BUFFER of LENGTH bytes.  On

     success the result is stored at the address given by R_SEXP.  With

     AUTODETECT set to 0, the data in BUFFER is expected to be in

     canonized format, with AUTODETECT set to 1 the parses any of the

     defined external formats.  If BUFFER does not hold a valid

     S-expression an error code is returned and R_SEXP set to `NULL'.

     Note, that the caller is responsible for releasing the newly

     allocated S-expression using `gcry_sexp_release'.



 -- Function: gcry_error_t gcry_sexp_create (gcry_sexp_t *R_SEXP,

          void *BUFFER, size_t LENGTH, int AUTODETECT,

          void (*FREEFNC)(void*))

     This function is identical to `gcry_sexp_new' but has an extra

     argument FREEFNC, which, when not set to `NULL', is expected to be

     a function to release the BUFFER; most likely the standard `free'

     function is used for this argument.  This has the effect of

     transferring the ownership of BUFFER to the created object in

     R_SEXP.  The advantage of using this function is that Libgcrypt

     might decide to directly use the provided buffer and thus avoid

     extra copying.



 -- Function: gcry_error_t gcry_sexp_sscan (gcry_sexp_t *R_SEXP,

          size_t *ERROFF, const char *BUFFER, size_t LENGTH)

     This is another variant of the above functions.  It behaves nearly

     identical but provides an ERROFF argument which will receive the

     offset into the buffer where the parsing stopped on error.



 -- Function: gcry_error_t gcry_sexp_build (gcry_sexp_t *R_SEXP,

          size_t *ERROFF, const char *FORMAT, ...)

     This function creates an internal S-expression from the string

     template FORMAT and stores it at the address of R_SEXP. If there

     is a parsing error, the function returns an appropriate error code

     and stores the offset into FORMAT where the parsing stopped in

     ERROFF.  The function supports a couple of printf-like formatting

     characters and expects arguments for some of these escape

     sequences right after FORMAT.  The following format characters are

     defined:



    `%m'

          The next argument is expected to be of type `gcry_mpi_t' and

          a copy of its value is inserted into the resulting

          S-expression.



    `%s'

          The next argument is expected to be of type `char *' and that

          string is inserted into the resulting S-expression.



    `%d'

          The next argument is expected to be of type `int' and its

          value ist inserted into the resulting S-expression.



    `%b'

          The next argument is expected to be of type `int' directly

          followed by an argument of type `char *'.  This represents a

          buffer of given length to be inserted into the resulting

          regular expression.



     No other format characters are defined and would return an error.

     Note, that the format character `%%' does not exists, because a

     percent sign is not a valid character in an S-expression.



 -- Function: void gcry_sexp_release (gcry_sexp_t SEXP)

     Release the S-expression object SEXP.



The next 2 functions are used to convert the internal representation

back into a regular external S-expression format and to show the

structure for debugging.



 -- Function: size_t gcry_sexp_sprint (gcry_sexp_t SEXP, int MODE,

          void *BUFFER, size_t MAXLENGTH)

     Copies the S-expression object SEXP into BUFFER using the format

     specified in MODE.  MAXLENGTH must be set to the allocated length

     of BUFFER.  The function returns the actual length of valid bytes

     put into BUFFER or 0 if the provided buffer is too short.  Passing

     `NULL' for BUFFER returns the required length for BUFFER.  For

     convenience reasons an extra byte with value 0 is appended to the

     buffer.



     The following formats are supported:



    `GCRYSEXP_FMT_DEFAULT'

          Returns a convenient external S-expression representation.



    `GCRYSEXP_FMT_CANON'

          Return the S-expression in canonical format.



    `GCRYSEXP_FMT_BASE64'

          Not currently supported.



    `GCRYSEXP_FMT_ADVANCED'

          Returns the S-expression in advanced format.



 -- Function: void gcry_sexp_dump (gcry_sexp_t SEXP)

     Dumps SEXP in a format suitable for debugging to Libgcrypt's

     logging stream.



Often canonical encoding is used in the external representation.  The

following function can be used to check for valid encoding and to learn

the length of the S-expression"



 -- Function: size_t gcry_sexp_canon_len (const unsigned char *BUFFER,

          size_t LENGTH, size_t *ERROFF, int *ERRCODE)

     Scan the canonical encoded BUFFER with implicit length values and

     return the actual length this S-expression uses.  For a valid

     S-expression it should never return 0.  If LENGTH is not 0, the

     maximum length to scan is given; this can be used for syntax

     checks of data passed from outside.  ERRCODE and ERROFF may both be

     passed as `NULL'.





There are a couple of functions to parse S-expressions and retrieve

elements:



 -- Function: gcry_sexp_t gcry_sexp_find_token (const gcry_sexp_t LIST,

          const char *TOKEN, size_t TOKLEN)

     Scan the S-expression for a sublist with a type (the car of the

     list) matching the string TOKEN.  If TOKLEN is not 0, the token is

     assumed to be raw memory of this length.  The function returns a

     newly allocated S-expression consisting of the found sublist or

     `NULL' when not found.



 -- Function: int gcry_sexp_length (const gcry_sexp_t LIST)

     Return the length of the LIST.  For a valid S-expression this

     should be at least 1.



 -- Function: gcry_sexp_t gcry_sexp_nth (const gcry_sexp_t LIST,

          int NUMBER)

     Create and return a new S-expression from the element with index

     NUMBER in LIST.  Note that the first element has the index 0.  If

     there is no such element, `NULL' is returned.



 -- Function: gcry_sexp_t gcry_sexp_car (const gcry_sexp_t LIST)

     Create and return a new S-expression from the first element in

     LIST; this called the "type" and should always exist and be a

     string. `NULL' is returned in case of a problem.



 -- Function: gcry_sexp_t gcry_sexp_cdr (const gcry_sexp_t LIST)

     Create and return a new list form all elements except for the

     first one.  Note, that this function may return an invalid

     S-expression because it is not guaranteed, that the type exists

     and is a string.  However, for parsing a complex S-expression it

     might be useful for intermediate lists.  Returns `NULL' on error.



 -- Function: const char * gcry_sexp_nth_data (const gcry_sexp_t LIST,

          int NUMBER, size_t *DATALEN)

     This function is used to get data from a LIST.  A pointer to the

     actual data with index NUMBER is returned and the length of this

     data will be stored to DATALEN.  If there is no data at the given

     index or the index represents another list, `NULL' is returned.

     *Take care:* The returned pointer is valid as long as LIST is not

     modified or released.



     Here is an example on how to extract and print the surname (Meier)

     from the S-expression `(Name Otto Meier (address Burgplatz 3))':



          size_t len;

          const char *name;



          name = gcry_sexp_nth_data (list, 2, &len);

          printf ("my name is %.*s\n", (int)len, name);



 -- Function: gcry_mpi_t gcry_sexp_nth_mpi (gcry_sexp_t LIST,

          int NUMBER, int MPIFMT)

     This function is used to get and convert data from a LIST. This

     data is assumed to be an MPI stored in the format described by

     MPIFMT and returned as a standard Libgcrypt MPI.  The caller must

     release this returned value using `gcry_mpi_release'.  If there is

     no data at the given index, the index represents a list or the

     value can't be converted to an MPI, `NULL' is returned.





File: gcrypt.info,  Node: MPI library,  Next: Utilities,  Prev: S-expressions,  Up: Top



11 MPI library

**************



* Menu:



* Data types::                  MPI related data types.

* Basic functions::             First steps with MPI numbers.

* MPI formats::                 External representation of MPIs.

* Calculations::                Performing MPI calculations.

* Comparisons::                 How to compare MPI values.

* Bit manipulations::           How to access single bits of MPI values.

* Miscellaneous::               Miscellaneous MPI functions.



   Public key cryptography is based on mathematics with large numbers.

To implement the public key functions, a library for handling these

large numbers is required.  Because of the general usefulness of such a

library, its interface is exposed by Libgcrypt.  The implementation is

based on an old release of GNU Multi-Precision Library (GMP) but in the

meantime heavily modified and stripped down to what is required for

cryptography. For a lot of CPUs, high performance assembler

implementations of some very low level functions are used to gain much

better performance than with the standard C implementation.



In the context of Libgcrypt and in most other applications, these large

numbers are called MPIs (multi-precision-integers).





File: gcrypt.info,  Node: Data types,  Next: Basic functions,  Up: MPI library



11.1 Data types

===============



 -- Data type: gcry_mpi_t

     The `gcry_mpi_t' type represents an object to hold an MPI.





File: gcrypt.info,  Node: Basic functions,  Next: MPI formats,  Prev: Data types,  Up: MPI library



11.2 Basic functions

====================



To work with MPIs, storage must be allocated and released for the

numbers.  This can be done with one of these functions:



 -- Function: gcry_mpi_t gcry_mpi_new (unsigned int NBITS)

     Allocate a new MPI object, initialize it to 0 and initially

     allocate enough memory for a number of at least NBITS.  This

     pre-allocation is only a small performance issue and not actually

     necessary because Libgcrypt automatically re-allocates the

     required memory.



 -- Function: gcry_mpi_t gcry_mpi_snew (unsigned int NBITS)

     This is identical to `gcry_mpi_new' but allocates the MPI in the so

     called "secure memory" which in turn will take care that all

     derived values will also be stored in this "secure memory".  Use

     this for highly confidential data like private key parameters.



 -- Function: gcry_mpi_t gcry_mpi_copy (const gcry_mpi_t A)

     Create a new MPI as the exact copy of A.



 -- Function: void gcry_mpi_release (gcry_mpi_t A)

     Release the MPI A and free all associated resources.  Passing

     `NULL' is allowed and ignored.  When a MPI stored in the "secure

     memory" is released, that memory gets wiped out immediately.



The simplest operations are used to assign a new value to an MPI:



 -- Function: gcry_mpi_t gcry_mpi_set (gcry_mpi_t W, const gcry_mpi_t U)

     Assign the value of U to W and return W.  If `NULL' is passed for

     W, a new MPI is allocated, set to the value of U and returned.



 -- Function: gcry_mpi_t gcry_mpi_set_ui (gcry_mpi_t W, unsigned long U)

     Assign the value of U to W and return W.  If `NULL' is passed for

     W, a new MPI is allocated, set to the value of U and returned.

     This function takes an `unsigned int' as type for U and thus it is

     only possible to set W to small values (usually up to the word

     size of the CPU).



 -- Function: void gcry_mpi_swap (gcry_mpi_t A, gcry_mpi_t B)

     Swap the values of A and B.





File: gcrypt.info,  Node: MPI formats,  Next: Calculations,  Prev: Basic functions,  Up: MPI library



11.3 MPI formats

================



The following functions are used to convert between an external

representation of an MPI and the internal one of Libgcrypt.



 -- Function: int gcry_mpi_scan (gcry_mpi_t *R_MPI,

          enum gcry_mpi_format FORMAT, const void *BUFFER,

          size_t BUFLEN, size_t *NSCANNED)

     Convert the external representation of an integer stored in BUFFER

     with a length of BUFLEN into a newly created MPI returned which

     will be stored at the address of R_MPI.  For certain formats the

     length argument is not required and may be passed as `0'.  After a

     successful operation the variable NSCANNED receives the number of

     bytes actually scanned unless NSCANNED was given as `NULL'. FORMAT

     describes the format of the MPI as stored in BUFFER:



    `GCRYMPI_FMT_STD'

          2-complement stored without a length header.



    `GCRYMPI_FMT_PGP'

          As used by OpenPGP (only defined as unsigned). This is

          basically `GCRYMPI_FMT_STD' with a 2 byte big endian length

          header.



    `GCRYMPI_FMT_SSH'

          As used in the Secure Shell protocol.  This is

          `GCRYMPI_FMT_STD' with a 4 byte big endian header.



    `GCRYMPI_FMT_HEX'

          Stored as a C style string with each byte of the MPI encoded

          as 2 hex digits.



    `GCRYMPI_FMT_USG'

          Simple unsigned integer.



     Note, that all of the above formats store the integer in big-endian

     format (MSB first).



 -- Function: int gcry_mpi_print (enum gcry_mpi_format FORMAT,

          unsigned char *BUFFER, size_t BUFLEN, size_t *NWRITTEN,

          const gcry_mpi_t A)

     Convert the MPI A into an external representation described by

     FORMAT (see above) and store it in the provided BUFFER which has a

     usable length of at least the BUFLEN bytes. If NWRITTEN is not

     NULL, it will receive the number of bytes actually stored in

     BUFFER after a successful operation.



 -- Function: int gcry_mpi_aprint (enum gcry_mpi_format FORMAT,

          unsigned char **BUFFER, size_t *NBYTES, const gcry_mpi_t A)

     Convert the MPI A into an external representation described by

     FORMAT (see above) and store it in a newly allocated buffer which

     address will be stored in the variable BUFFER points to.  The

     number of bytes stored in this buffer will be stored in the

     variable NBYTES points to, unless NBYTES is `NULL'.



 -- Function: void gcry_mpi_dump (const gcry_mpi_t A)

     Dump the value of A in a format suitable for debugging to

     Libgcrypt's logging stream.  Note that one leading space but no

     trailing space or linefeed will be printed.  It is okay to pass

     `NULL' for A.





File: gcrypt.info,  Node: Calculations,  Next: Comparisons,  Prev: MPI formats,  Up: MPI library



11.4 Calculations

=================



Basic arithmetic operations:



 -- Function: void gcry_mpi_add (gcry_mpi_t W, gcry_mpi_t U,

          gcry_mpi_t V)

     W = U + V.



 -- Function: void gcry_mpi_add_ui (gcry_mpi_t W, gcry_mpi_t U,

          unsigned long V)

     W = U + V.  Note, that V is an unsigned integer.



 -- Function: void gcry_mpi_addm (gcry_mpi_t W, gcry_mpi_t U,

          gcry_mpi_t V, gcry_mpi_t M)

     W = U + V \bmod M.



 -- Function: void gcry_mpi_sub (gcry_mpi_t W, gcry_mpi_t U,

          gcry_mpi_t V)

     W = U - V.



 -- Function: void gcry_mpi_sub_ui (gcry_mpi_t W, gcry_mpi_t U,

          unsigned long V)

     W = U - V.  V is an unsigned integer.



 -- Function: void gcry_mpi_subm (gcry_mpi_t W, gcry_mpi_t U,

          gcry_mpi_t V, gcry_mpi_t M)

     W = U - V \bmod M.



 -- Function: void gcry_mpi_mul (gcry_mpi_t W, gcry_mpi_t U,

          gcry_mpi_t V)

     W = U * V.



 -- Function: void gcry_mpi_mul_ui (gcry_mpi_t W, gcry_mpi_t U,

          unsigned long V)

     W = U * V.  V is an unsigned integer.



 -- Function: void gcry_mpi_mulm (gcry_mpi_t W, gcry_mpi_t U,

          gcry_mpi_t V, gcry_mpi_t M)

     W = U * V \bmod M.



 -- Function: void gcry_mpi_mul_2exp (gcry_mpi_t W, gcry_mpi_t U,

          unsigned long E)

     W = U * 2^e.



 -- Function: void gcry_mpi_div (gcry_mpi_t Q, gcry_mpi_t R,

          gcry_mpi_t DIVIDEND, gcry_mpi_t DIVISOR, int ROUND)

     Q = DIVIDEND / DIVISOR, R = DIVIDEND \bmod DIVISOR.  Q and R may

     be passed as `NULL'.  ROUND should be negative or 0.



 -- Function: void gcry_mpi_mod (gcry_mpi_t R, gcry_mpi_t DIVIDEND,

          gcry_mpi_t DIVISOR)

     R = DIVIDEND \bmod DIVISOR.



 -- Function: void gcry_mpi_powm (gcry_mpi_t W, const gcry_mpi_t B,

          const gcry_mpi_t E, const gcry_mpi_t M)

     W = B^e \bmod M.



 -- Function: int gcry_mpi_gcd (gcry_mpi_t G, gcry_mpi_t A,

          gcry_mpi_t B)

     Set G to the greatest common divisor of A and B.  Return true if

     the G is 1.



 -- Function: int gcry_mpi_invm (gcry_mpi_t X, gcry_mpi_t A,

          gcry_mpi_t M)

     Set X to the multiplicative inverse of A \bmod M.  Return true if

     the inverse exists.





File: gcrypt.info,  Node: Comparisons,  Next: Bit manipulations,  Prev: Calculations,  Up: MPI library



11.5 Comparisons

================



The next 2 functions are used to compare MPIs:



 -- Function: int gcry_mpi_cmp (const gcry_mpi_t U, const gcry_mpi_t V)

     Compare the big integer number U and V returning 0 for equality, a

     positive value for U > V and a negative for U < V.



 -- Function: int gcry_mpi_cmp_ui (const gcry_mpi_t U, unsigned long V)

     Compare the big integer number U with the unsigned integer V

     returning 0 for equality, a positive value for U > V and a

     negative for U < V.





File: gcrypt.info,  Node: Bit manipulations,  Next: Miscellaneous,  Prev: Comparisons,  Up: MPI library



11.6 Bit manipulations

======================



There are a couple of functions to get information on arbitrary bits in

an MPI and to set or clear them:



 -- Function: unsigned int gcry_mpi_get_nbits (gcry_mpi_t A)

     Return the number of bits required to represent A.



 -- Function: int gcry_mpi_test_bit (gcry_mpi_t A, unsigned int N)

     Return true if bit number N (counting from 0) is set in A.



 -- Function: void gcry_mpi_set_bit (gcry_mpi_t A, unsigned int N)

     Set bit number N in A.



 -- Function: void gcry_mpi_clear_bit (gcry_mpi_t A, unsigned int N)

     Clear bit number N in A.



 -- Function: void gcry_mpi_set_highbit (gcry_mpi_t A, unsigned int N)

     Set bit number N in A and clear all bits greater than N.



 -- Function: void gcry_mpi_clear_highbit (gcry_mpi_t A, unsigned int N)

     Clear bit number N in A and all bits greater than N.



 -- Function: void gcry_mpi_rshift (gcry_mpi_t X, gcry_mpi_t A,

          unsigned int N)

     Shift the value of A by N bits to the right and store the result

     in X.





File: gcrypt.info,  Node: Miscellaneous,  Prev: Bit manipulations,  Up: MPI library



11.7 Miscellanous

=================



 -- Function: gcry_mpi_t gcry_mpi_set_opaque (gcry_mpi_t A, void *P,

          unsigned int NBITS)

     Store NBITS of the value P points to in A and mark A as an opaque

     value (i.e. an value that can't be used for any math calculation

     and is only used to store an arbitrary bit pattern in A).



     WARNING: Never use an opaque MPI for actual math operations.  The

     only valid functions are gcry_mpi_get_opaque and gcry_mpi_release.

     Use gcry_mpi_scan to convert a string of arbitrary bytes into an

     MPI.





 -- Function: void * gcry_mpi_get_opaque (gcry_mpi_t A,

          unsigned int *NBITS)

     Return a pointer to an opaque value stored in A and return its

     size in NBITS.  Note, that the returned pointer is still owned by

     A and that the function should never be used for an non-opaque MPI.



 -- Function: void gcry_mpi_set_flag (gcry_mpi_t A,

          enum gcry_mpi_flag FLAG)

     Set the FLAG for the MPI A.  Currently only the flag

     `GCRYMPI_FLAG_SECURE' is allowed to convert A into an MPI stored

     in "secure memory".



 -- Function: void gcry_mpi_clear_flag (gcry_mpi_t A,

          enum gcry_mpi_flag FLAG)

     Clear FLAG for the big integer A.  Note, that this function is

     currently useless as no flags are allowed.



 -- Function: int gcry_mpi_get_flag (gcry_mpi_t A,

          enum gcry_mpi_flag FLAG)

     Return true when the FLAG is set for A.



 -- Function: void gcry_mpi_randomize (gcry_mpi_t W,

          unsigned int NBITS, enum gcry_random_level LEVEL)

     Set the big integer W to a random value of NBITS, using random

     data quality of level LEVEL.  In case NBITS is not a multiple of a

     byte, NBITS is rounded up to the next byte boundary.





File: gcrypt.info,  Node: Utilities,  Next: Library Copying,  Prev: MPI library,  Up: Top



12 Utilities

************



* Menu:



* Memory allocation::           Functions related with memory allocation.





File: gcrypt.info,  Node: Memory allocation,  Up: Utilities



12.1 Memory allocation

======================



 -- Function: void *gcry_malloc (size_t N)

     This function tries to allocate N bytes of memory.  On success it

     returns a pointer to the memory area, in an out-of-core condition,

     it returns NULL.



 -- Function: void *gcry_malloc_secure (size_t N)

     Like `gcry_malloc', but uses secure memory.



 -- Function: void *gcry_calloc (size_t N)

     This function tries to allocate N bytes of cleared memory (i.e.

     memory that is initialized with zero bytes).  On success it

     returns a pointer to the memory area, in an out-of-core condition,

     it returns NULL.



 -- Function: void *gcry_calloc_secure (size_t N)

     Like `gcry_calloc', but uses secure memory.



 -- Function: void *gcry_realloc (void *P, size_t N)

     This function tries to resize the memory area pointed to by P to N

     bytes.  On success it returns a pointer to the new memory area, in

     an out-of-core condition, it returns NULL.  Depending on whether

     the memory pointed to by P is secure memory or not, gcry_realloc

     tries to use secure memory as well.



 -- Function: void gcry_free (void *P)

     Release the memory area pointed to by P.





File: gcrypt.info,  Node: Library Copying,  Next: Copying,  Prev: Utilities,  Up: Top



Appendix A GNU LESSER GENERAL PUBLIC LICENSE

********************************************



                      Version 2.1, February 1999



     Copyright (C) 1991, 1999 Free Software Foundation, Inc.

     59 Temple Place - Suite 330, Boston, MA 02111-1307, USA



     Everyone is permitted to copy and distribute verbatim copies

     of this license document, but changing it is not allowed.



     [This is the first released version of the Lesser GPL.  It also counts

     as the successor of the GNU Library Public License, version 2, hence the

     version number 2.1.]



A.0.1 Preamble

--------------



The licenses for most software are designed to take away your freedom

to share and change it.  By contrast, the GNU General Public Licenses

are intended to guarantee your freedom to share and change free

software--to make sure the software is free for all its users.



   This license, the Lesser General Public License, applies to some

specially designated software--typically libraries--of the Free

Software Foundation and other authors who decide to use it.  You can use

it too, but we suggest you first think carefully about whether this

license or the ordinary General Public License is the better strategy to

use in any particular case, based on the explanations below.



   When we speak of free software, we are referring to freedom of use,

not price.  Our General Public Licenses are designed to make sure that

you have the freedom to distribute copies of free software (and charge

for this service if you wish); that you receive source code or can get

it if you want it; that you can change the software and use pieces of it

in new free programs; and that you are informed that you can do these

things.



   To protect your rights, we need to make restrictions that forbid

distributors to deny you these rights or to ask you to surrender these

rights.  These restrictions translate to certain responsibilities for

you if you distribute copies of the library or if you modify it.



   For example, if you distribute copies of the library, whether gratis

or for a fee, you must give the recipients all the rights that we gave

you.  You must make sure that they, too, receive or can get the source

code.  If you link other code with the library, you must provide

complete object files to the recipients, so that they can relink them

with the library after making changes to the library and recompiling

it.  And you must show them these terms so they know their rights.



   We protect your rights with a two-step method: (1) we copyright the

library, and (2) we offer you this license, which gives you legal

permission to copy, distribute and/or modify the library.



   To protect each distributor, we want to make it very clear that

there is no warranty for the free library.  Also, if the library is

modified by someone else and passed on, the recipients should know that

what they have is not the original version, so that the original

author's reputation will not be affected by problems that might be

introduced by others.



   Finally, software patents pose a constant threat to the existence of

any free program.  We wish to make sure that a company cannot

effectively restrict the users of a free program by obtaining a

restrictive license from a patent holder.  Therefore, we insist that

any patent license obtained for a version of the library must be

consistent with the full freedom of use specified in this license.



   Most GNU software, including some libraries, is covered by the

ordinary GNU General Public License.  This license, the GNU Lesser

General Public License, applies to certain designated libraries, and is

quite different from the ordinary General Public License.  We use this

license for certain libraries in order to permit linking those

libraries into non-free programs.



   When a program is linked with a library, whether statically or using

a shared library, the combination of the two is legally speaking a

combined work, a derivative of the original library.  The ordinary

General Public License therefore permits such linking only if the

entire combination fits its criteria of freedom.  The Lesser General

Public License permits more lax criteria for linking other code with

the library.



   We call this license the "Lesser" General Public License because it

does _Less_ to protect the user's freedom than the ordinary General

Public License.  It also provides other free software developers Less

of an advantage over competing non-free programs.  These disadvantages

are the reason we use the ordinary General Public License for many

libraries.  However, the Lesser license provides advantages in certain

special circumstances.



   For example, on rare occasions, there may be a special need to

encourage the widest possible use of a certain library, so that it

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                      END OF TERMS AND CONDITIONS

A.0.2 How to Apply These Terms to Your New Libraries

----------------------------------------------------



If you develop a new library, and you want it to be of the greatest

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     ONE LINE TO GIVE THE LIBRARY'S NAME AND AN IDEA OF WHAT IT DOES.

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     This library is distributed in the hope that it will be useful, but

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     SIGNATURE OF TY COON, 1 April 1990

     Ty Coon, President of Vice



   That's all there is to it!





File: gcrypt.info,  Node: Copying,  Next: Concept Index,  Prev: Library Copying,  Up: Top



Appendix B GNU GENERAL PUBLIC LICENSE

*************************************



                         Version 2, June 1991



     Copyright (C) 1989, 1991 Free Software Foundation, Inc.

     59 Temple Place - Suite 330, Boston, MA 02111-1307, USA



     Everyone is permitted to copy and distribute verbatim copies

     of this license document, but changing it is not allowed.



B.0.1 Preamble

--------------



The licenses for most software are designed to take away your freedom

to share and change it.  By contrast, the GNU General Public License is

intended to guarantee your freedom to share and change free

software--to make sure the software is free for all its users.  This

General Public License applies to most of the Free Software

Foundation's software and to any other program whose authors commit to

using it.  (Some other Free Software Foundation software is covered by

the GNU Library General Public License instead.)  You can apply it to

your programs, too.



   When we speak of free software, we are referring to freedom, not

price.  Our General Public Licenses are designed to make sure that you

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These restrictions translate to certain responsibilities for you if you

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   The precise terms and conditions for copying, distribution and

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    TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

  1. This License applies to any program or other work which contains a

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     Thus, it is not the intent of this section to claim rights or

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  4. You may copy and distribute the Program (or a work based on it,

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          years, to give any third party, for a charge no more than your

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     However, as a special exception, the source code distributed need

     not include anything that is normally distributed (in either

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     If distribution of executable or object code is made by offering

     access to copy from a designated place, then offering equivalent

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     distribution of the source code, even though third parties are not

     compelled to copy the source along with the object code.



  5. You may not copy, modify, sublicense, or distribute the Program

     except as expressly provided under this License.  Any attempt

     otherwise to copy, modify, sublicense or distribute the Program is

     void, and will automatically terminate your rights under this

     License.  However, parties who have received copies, or rights,

     from you under this License will not have their licenses

     terminated so long as such parties remain in full compliance.



  6. You are not required to accept this License, since you have not

     signed it.  However, nothing else grants you permission to modify

     or distribute the Program or its derivative works.  These actions

     are prohibited by law if you do not accept this License.

     Therefore, by modifying or distributing the Program (or any work

     based on the Program), you indicate your acceptance of this

     License to do so, and all its terms and conditions for copying,

     distributing or modifying the Program or works based on it.



  7. Each time you redistribute the Program (or any work based on the

     Program), the recipient automatically receives a license from the

     original licensor to copy, distribute or modify the Program

     subject to these terms and conditions.  You may not impose any

     further restrictions on the recipients' exercise of the rights

     granted herein.  You are not responsible for enforcing compliance

     by third parties to this License.



  8. If, as a consequence of a court judgment or allegation of patent

     infringement or for any other reason (not limited to patent

     issues), conditions are imposed on you (whether by court order,

     agreement or otherwise) that contradict the conditions of this

     License, they do not excuse you from the conditions of this

     License.  If you cannot distribute so as to satisfy simultaneously

     your obligations under this License and any other pertinent

     obligations, then as a consequence you may not distribute the

     Program at all.  For example, if a patent license would not permit

     royalty-free redistribution of the Program by all those who

     receive copies directly or indirectly through you, then the only

     way you could satisfy both it and this License would be to refrain

     entirely from distribution of the Program.



     If any portion of this section is held invalid or unenforceable

     under any particular circumstance, the balance of the section is

     intended to apply and the section as a whole is intended to apply

     in other circumstances.



     It is not the purpose of this section to induce you to infringe any

     patents or other property right claims or to contest validity of

     any such claims; this section has the sole purpose of protecting

     the integrity of the free software distribution system, which is

     implemented by public license practices.  Many people have made

     generous contributions to the wide range of software distributed

     through that system in reliance on consistent application of that

     system; it is up to the author/donor to decide if he or she is

     willing to distribute software through any other system and a

     licensee cannot impose that choice.



     This section is intended to make thoroughly clear what is believed

     to be a consequence of the rest of this License.



  9. If the distribution and/or use of the Program is restricted in

     certain countries either by patents or by copyrighted interfaces,

     the original copyright holder who places the Program under this

     License may add an explicit geographical distribution limitation

     excluding those countries, so that distribution is permitted only

     in or among countries not thus excluded.  In such case, this

     License incorporates the limitation as if written in the body of

     this License.



 10. The Free Software Foundation may publish revised and/or new

     versions of the General Public License from time to time.  Such

     new versions will be similar in spirit to the present version, but

     may differ in detail to address new problems or concerns.



     Each version is given a distinguishing version number.  If the

     Program specifies a version number of this License which applies

     to it and "any later version", you have the option of following

     the terms and conditions either of that version or of any later

     version published by the Free Software Foundation.  If the Program

     does not specify a version number of this License, you may choose

     any version ever published by the Free Software Foundation.



 11. If you wish to incorporate parts of the Program into other free

     programs whose distribution conditions are different, write to the

     author to ask for permission.  For software which is copyrighted

     by the Free Software Foundation, write to the Free Software

     Foundation; we sometimes make exceptions for this.  Our decision

     will be guided by the two goals of preserving the free status of

     all derivatives of our free software and of promoting the sharing

     and reuse of software generally.



                                NO WARRANTY

 12. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO

     WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE

     LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT

     HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT

     WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT

     NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND

     FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS TO THE

     QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE

     PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY

     SERVICING, REPAIR OR CORRECTION.



 13. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN

     WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY

     MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE

     LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL,

     INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR

     INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF

     DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU

     OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY

     OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN

     ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.



                      END OF TERMS AND CONDITIONS

How to Apply These Terms to Your New Programs

=============================================



If you develop a new program, and you want it to be of the greatest

possible use to the public, the best way to achieve this is to make it

free software which everyone can redistribute and change under these

terms.



   To do so, attach the following notices to the program.  It is safest

to attach them to the start of each source file to most effectively

convey the exclusion of warranty; and each file should have at least

the "copyright" line and a pointer to where the full notice is found.



     ONE LINE TO GIVE THE PROGRAM'S NAME AND AN IDEA OF WHAT IT DOES.

     Copyright (C) 19YY  NAME OF AUTHOR



     This program is free software; you can redistribute it and/or

     modify it under the terms of the GNU General Public License

     as published by the Free Software Foundation; either version 2

     of the License, or (at your option) any later version.



     This program is distributed in the hope that it will be useful,

     but WITHOUT ANY WARRANTY; without even the implied warranty of

     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

     GNU General Public License for more details.



     You should have received a copy of the GNU General Public License along

     with this program; if not, write to the Free Software Foundation, Inc.,

     59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.



   Also add information on how to contact you by electronic and paper

mail.



   If the program is interactive, make it output a short notice like

this when it starts in an interactive mode:



     Gnomovision version 69, Copyright (C) 19YY NAME OF AUTHOR

     Gnomovision comes with ABSOLUTELY NO WARRANTY; for details

     type `show w'.  This is free software, and you are welcome

     to redistribute it under certain conditions; type `show c'

     for details.



   The hypothetical commands `show w' and `show c' should show the

appropriate parts of the General Public License.  Of course, the

commands you use may be called something other than `show w' and `show

c'; they could even be mouse-clicks or menu items--whatever suits your

program.



   You should also get your employer (if you work as a programmer) or

your school, if any, to sign a "copyright disclaimer" for the program,

if necessary.  Here is a sample; alter the names:



     Yoyodyne, Inc., hereby disclaims all copyright

     interest in the program `Gnomovision'

     (which makes passes at compilers) written

     by James Hacker.



     SIGNATURE OF TY COON, 1 April 1989

     Ty Coon, President of Vice



   This General Public License does not permit incorporating your

program into proprietary programs.  If your program is a subroutine

library, you may consider it more useful to permit linking proprietary

applications with the library.  If this is what you want to do, use the

GNU Library General Public License instead of this License.





File: gcrypt.info,  Node: Concept Index,  Next: Function and Data Index,  Prev: Copying,  Up: Top



Concept Index

*************



�[index�]

* Menu:



* error codes:                           Error Values.          (line 6)

* error codes, list of <1>:              Error Codes.           (line 6)

* error codes, list of:                  Error Sources.         (line 6)

* error codes, printing of:              Error Strings.         (line 6)

* error sources:                         Error Values.          (line 6)

* error sources, printing of:            Error Strings.         (line 6)

* error strings:                         Error Strings.         (line 6)

* error values:                          Error Values.          (line 6)

* error values, printing of:             Error Strings.         (line 6)

* GPL, GNU General Public License:       Copying.               (line 6)

* LGPL, Lesser General Public License:   Library Copying.       (line 6)





File: gcrypt.info,  Node: Function and Data Index,  Prev: Concept Index,  Up: Top



Function and Data Index

***********************



�[index�]

* Menu:



* *:                                     Retrieving random numbers.

                                                              (line  13)

* *gcry_calloc:                          Memory allocation.   (line  15)

* *gcry_calloc_secure:                   Memory allocation.   (line  21)

* *gcry_malloc:                          Memory allocation.   (line   7)

* *gcry_malloc_secure:                   Memory allocation.   (line  12)

* *gcry_realloc:                         Memory allocation.   (line  24)

* AM_PATH_LIBGCRYPT:                     Building sources using Automake.

                                                              (line  13)

* char <1>:                              Working with hash algorithms.

                                                              (line 117)

* char <2>:                              General cipher functions.

                                                              (line  39)

* char:                                  Initializing the library.

                                                              (line  13)

* enum:                                  Quality of random numbers.

                                                              (line   9)

* gcry_ac_close:                         Working with handles.

                                                              (line  21)

* gcry_ac_data_clear:                    Working with sets of data.

                                                              (line  68)

* gcry_ac_data_copy:                     Working with sets of data.

                                                              (line  48)

* gcry_ac_data_decrypt:                  Using cryptographic functions.

                                                              (line  22)

* gcry_ac_data_destroy:                  Working with sets of data.

                                                              (line  36)

* gcry_ac_data_encrypt:                  Using cryptographic functions.

                                                              (line  15)

* gcry_ac_data_get_index:                Working with sets of data.

                                                              (line  62)

* gcry_ac_data_get_name:                 Working with sets of data.

                                                              (line  55)

* gcry_ac_data_new:                      Working with sets of data.

                                                              (line  33)

* gcry_ac_data_set:                      Working with sets of data.

                                                              (line  40)

* gcry_ac_data_sign:                     Using cryptographic functions.

                                                              (line  30)

* gcry_ac_data_t:                        Working with sets of data.

                                                              (line  19)

* gcry_ac_data_verify:                   Using cryptographic functions.

                                                              (line  36)

* gcry_ac_id_t:                          Available asymmetric algorithms.

                                                              (line  11)

* gcry_ac_id_to_name:                    Handle-independent functions.

                                                              (line   8)

* gcry_ac_key_data_get:                  Working with keys.   (line  92)

* gcry_ac_key_destroy:                   Working with keys.   (line  85)

* gcry_ac_key_get_grip:                  Working with keys.   (line 104)

* gcry_ac_key_get_nbits:                 Working with keys.   (line 100)

* gcry_ac_key_init:                      Working with keys.   (line  30)

* gcry_ac_key_pair_destroy:              Working with keys.   (line  89)

* gcry_ac_key_pair_extract:              Working with keys.   (line  82)

* gcry_ac_key_pair_generate:             Working with keys.   (line  36)

* gcry_ac_key_pair_t:                    Working with keys.   (line  20)

* gcry_ac_key_t:                         Working with keys.   (line  16)

* gcry_ac_key_test:                      Working with keys.   (line  96)

* gcry_ac_key_type_t:                    Working with keys.   (line   7)

* gcry_ac_name_to_id:                    Handle-independent functions.

                                                              (line  13)

* gcry_ac_open:                          Working with handles.

                                                              (line  11)

* gcry_cipher_algo_info:                 General cipher functions.

                                                              (line  12)

* gcry_cipher_close:                     Working with cipher handles.

                                                              (line  52)

* gcry_cipher_ctl:                       Working with cipher handles.

                                                              (line 152)

* gcry_cipher_decrypt:                   Working with cipher handles.

                                                              (line 122)

* gcry_cipher_decrypt_t:                 Cipher modules.      (line  80)

* gcry_cipher_encrypt:                   Working with cipher handles.

                                                              (line 104)

* gcry_cipher_encrypt_t:                 Cipher modules.      (line  75)

* gcry_cipher_info:                      Working with cipher handles.

                                                              (line 161)

* gcry_cipher_list:                      Cipher modules.      (line 106)

* gcry_cipher_map_name:                  General cipher functions.

                                                              (line  45)

* gcry_cipher_mode_from_oid:             General cipher functions.

                                                              (line  50)

* gcry_cipher_oid_spec_t:                Cipher modules.      (line  60)

* gcry_cipher_open:                      Working with cipher handles.

                                                              (line  11)

* gcry_cipher_register:                  Cipher modules.      (line  96)

* gcry_cipher_reset:                     Working with cipher handles.

                                                              (line  92)

* gcry_cipher_setctr:                    Working with cipher handles.

                                                              (line  84)

* gcry_cipher_setiv:                     Working with cipher handles.

                                                              (line  76)

* gcry_cipher_setkey:                    Working with cipher handles.

                                                              (line  59)

* gcry_cipher_setkey_t:                  Cipher modules.      (line  70)

* gcry_cipher_spec_t:                    Cipher modules.      (line  12)

* gcry_cipher_stdecrypt_t:               Cipher modules.      (line  90)

* gcry_cipher_stencrypt_t:               Cipher modules.      (line  85)

* gcry_cipher_sync:                      Working with cipher handles.

                                                              (line 142)

* gcry_cipher_unregister:                Cipher modules.      (line 101)

* gcry_control:                          Controlling the library.

                                                              (line   7)

* gcry_create_nonce:                     Retrieving random numbers.

                                                              (line  24)

* gcry_err_code:                         Error Values.        (line  43)

* gcry_err_code_from_errno:              Error Values.        (line  95)

* gcry_err_code_t:                       Error Values.        (line   7)

* gcry_err_code_to_errno:                Error Values.        (line 100)

* gcry_err_make:                         Error Values.        (line  57)

* gcry_err_make_from_errno:              Error Values.        (line  81)

* gcry_err_source:                       Error Values.        (line  49)

* gcry_err_source_t:                     Error Values.        (line  14)

* gcry_error:                            Error Values.        (line  64)

* gcry_error_from_errno:                 Error Values.        (line  86)

* gcry_error_t:                          Error Values.        (line  25)

* gcry_free:                             Memory allocation.   (line  31)

* gcry_handler_alloc_t:                  Allocation handler.  (line  12)

* gcry_handler_error_t:                  Error handler.       (line  20)

* gcry_handler_free_t:                   Allocation handler.  (line  24)

* gcry_handler_log_t:                    Logging handler.     (line   7)

* gcry_handler_no_mem_t:                 Error handler.       (line  10)

* gcry_handler_progress_t:               Progress handler.    (line  10)

* gcry_handler_realloc_t:                Allocation handler.  (line  20)

* gcry_handler_secure_check_t:           Allocation handler.  (line  16)

* gcry_md_close:                         Working with hash algorithms.

                                                              (line  59)

* gcry_md_copy:                          Working with hash algorithms.

                                                              (line  80)

* gcry_md_enable:                        Working with hash algorithms.

                                                              (line  43)

* gcry_md_final:                         Working with hash algorithms.

                                                              (line 107)

* gcry_md_final_t:                       Hash algorithm modules.

                                                              (line  73)

* gcry_md_get_algo:                      Working with hash algorithms.

                                                              (line 193)

* gcry_md_get_asnoid:                    Working with hash algorithms.

                                                              (line 165)

* gcry_md_hash_buffer:                   Working with hash algorithms.

                                                              (line 132)

* gcry_md_init_t:                        Hash algorithm modules.

                                                              (line  65)

* gcry_md_is_enabled:                    Working with hash algorithms.

                                                              (line 204)

* gcry_md_is_secure:                     Working with hash algorithms.

                                                              (line 199)

* gcry_md_list:                          Hash algorithm modules.

                                                              (line  91)

* gcry_md_map_name:                      Working with hash algorithms.

                                                              (line 155)

* gcry_md_oid_spec_t:                    Hash algorithm modules.

                                                              (line  57)

* gcry_md_open:                          Working with hash algorithms.

                                                              (line  11)

* gcry_md_putc:                          Working with hash algorithms.

                                                              (line  97)

* gcry_md_read_t:                        Hash algorithm modules.

                                                              (line  77)

* gcry_md_register:                      Hash algorithm modules.

                                                              (line  82)

* gcry_md_reset:                         Working with hash algorithms.

                                                              (line  68)

* gcry_md_setkey:                        Working with hash algorithms.

                                                              (line  52)

* gcry_md_spec_t:                        Hash algorithm modules.

                                                              (line  12)

* gcry_md_start_debug:                   Working with hash algorithms.

                                                              (line 215)

* gcry_md_stop_debug:                    Working with hash algorithms.

                                                              (line 223)

* gcry_md_test_algo:                     Working with hash algorithms.

                                                              (line 178)

* gcry_md_unregister:                    Hash algorithm modules.

                                                              (line  87)

* gcry_md_write:                         Working with hash algorithms.

                                                              (line  92)

* gcry_md_write_t:                       Hash algorithm modules.

                                                              (line  69)

* gcry_module_t:                         Modules.             (line  10)

* gcry_mpi_add:                          Calculations.        (line  10)

* gcry_mpi_add_ui:                       Calculations.        (line  14)

* gcry_mpi_addm:                         Calculations.        (line  18)

* gcry_mpi_aprint:                       MPI formats.         (line  53)

* gcry_mpi_clear_bit:                    Bit manipulations.   (line  19)

* gcry_mpi_clear_flag:                   Miscellaneous.       (line  32)

* gcry_mpi_clear_highbit:                Bit manipulations.   (line  25)

* gcry_mpi_cmp:                          Comparisons.         (line   9)

* gcry_mpi_cmp_ui:                       Comparisons.         (line  13)

* gcry_mpi_copy:                         Basic functions.     (line  23)

* gcry_mpi_div:                          Calculations.        (line  50)

* gcry_mpi_dump:                         MPI formats.         (line  60)

* gcry_mpi_gcd:                          Calculations.        (line  63)

* gcry_mpi_get_flag:                     Miscellaneous.       (line  37)

* gcry_mpi_get_nbits:                    Bit manipulations.   (line  10)

* gcry_mpi_get_opaque:                   Miscellaneous.       (line  20)

* gcry_mpi_invm:                         Calculations.        (line  68)

* gcry_mpi_mod:                          Calculations.        (line  55)

* gcry_mpi_mul:                          Calculations.        (line  34)

* gcry_mpi_mul_2exp:                     Calculations.        (line  46)

* gcry_mpi_mul_ui:                       Calculations.        (line  38)

* gcry_mpi_mulm:                         Calculations.        (line  42)

* gcry_mpi_new:                          Basic functions.     (line  10)

* gcry_mpi_powm:                         Calculations.        (line  59)

* gcry_mpi_print:                        MPI formats.         (line  45)

* gcry_mpi_randomize:                    Miscellaneous.       (line  41)

* gcry_mpi_release:                      Basic functions.     (line  26)

* gcry_mpi_rshift:                       Bit manipulations.   (line  29)

* gcry_mpi_scan:                         MPI formats.         (line  12)

* gcry_mpi_set:                          Basic functions.     (line  33)

* gcry_mpi_set_bit:                      Bit manipulations.   (line  16)

* gcry_mpi_set_flag:                     Miscellaneous.       (line  26)

* gcry_mpi_set_highbit:                  Bit manipulations.   (line  22)

* gcry_mpi_set_opaque:                   Miscellaneous.       (line   8)

* gcry_mpi_set_ui:                       Basic functions.     (line  37)

* gcry_mpi_snew:                         Basic functions.     (line  17)

* gcry_mpi_sub:                          Calculations.        (line  22)

* gcry_mpi_sub_ui:                       Calculations.        (line  26)

* gcry_mpi_subm:                         Calculations.        (line  30)

* gcry_mpi_swap:                         Basic functions.     (line  44)

* gcry_mpi_t:                            Data types.          (line   7)

* gcry_mpi_test_bit:                     Bit manipulations.   (line  13)

* gcry_pk_algo_info:                     General public-key related Functions.

                                                              (line  46)

* gcry_pk_algo_name:                     General public-key related Functions.

                                                              (line  10)

* gcry_pk_check_secret_key_t:            Public key modules.  (line  91)

* gcry_pk_ctl:                           General public-key related Functions.

                                                              (line  96)

* gcry_pk_decrypt:                       Cryptographic Functions.

                                                              (line  85)

* gcry_pk_decrypt_t:                     Public key modules.  (line 101)

* gcry_pk_encrypt:                       Cryptographic Functions.

                                                              (line  29)

* gcry_pk_encrypt_t:                     Public key modules.  (line  96)

* gcry_pk_generate_t:                    Public key modules.  (line  86)

* gcry_pk_genkey:                        General public-key related Functions.

                                                              (line 111)

* gcry_pk_get_keygrip:                   General public-key related Functions.

                                                              (line  28)

* gcry_pk_get_nbits:                     General public-key related Functions.

                                                              (line  23)

* gcry_pk_get_nbits_t:                   Public key modules.  (line 116)

* gcry_pk_list:                          Public key modules.  (line 131)

* gcry_pk_map_name:                      General public-key related Functions.

                                                              (line  15)

* gcry_pk_register:                      Public key modules.  (line 121)

* gcry_pk_sign:                          Cryptographic Functions.

                                                              (line 117)

* gcry_pk_sign_t:                        Public key modules.  (line 106)

* gcry_pk_spec_t:                        Public key modules.  (line  12)

* gcry_pk_test_algo:                     General public-key related Functions.

                                                              (line  19)

* gcry_pk_testkey:                       General public-key related Functions.

                                                              (line  39)

* gcry_pk_unregister:                    Public key modules.  (line 127)

* gcry_pk_verify:                        Cryptographic Functions.

                                                              (line 170)

* gcry_pk_verify_t:                      Public key modules.  (line 111)

* gcry_randomize:                        Retrieving random numbers.

                                                              (line   8)

* gcry_set_allocation_handler:           Allocation handler.  (line  34)

* gcry_set_fatalerror_handler:           Error handler.       (line  25)

* gcry_set_log_handler:                  Logging handler.     (line  12)

* gcry_set_outofcore_handler:            Error handler.       (line  15)

* gcry_set_progress_handler:             Progress handler.    (line  21)

* gcry_sexp_build:                       Working with S-expressions.

                                                              (line  43)

* gcry_sexp_canon_len:                   Working with S-expressions.

                                                              (line 116)

* gcry_sexp_car:                         Working with S-expressions.

                                                              (line 146)

* gcry_sexp_cdr:                         Working with S-expressions.

                                                              (line 151)

* gcry_sexp_create:                      Working with S-expressions.

                                                              (line  26)

* gcry_sexp_dump:                        Working with S-expressions.

                                                              (line 107)

* gcry_sexp_find_token:                  Working with S-expressions.

                                                              (line 129)

* gcry_sexp_length:                      Working with S-expressions.

                                                              (line 136)

* gcry_sexp_new:                         Working with S-expressions.

                                                              (line  13)

* gcry_sexp_nth:                         Working with S-expressions.

                                                              (line 141)

* gcry_sexp_nth_data:                    Working with S-expressions.

                                                              (line 159)

* gcry_sexp_nth_mpi:                     Working with S-expressions.

                                                              (line 177)

* gcry_sexp_release:                     Working with S-expressions.

                                                              (line  76)

* gcry_sexp_sprint:                      Working with S-expressions.

                                                              (line  84)

* gcry_sexp_sscan:                       Working with S-expressions.

                                                              (line  37)

* gcry_sexp_t:                           Data types for S-expressions.

                                                              (line   7)

* gcry_strerror:                         Error Strings.       (line   7)

* gcry_strsource:                        Error Strings.       (line  13)

* int <1>:                               Working with sets of data.

                                                              (line  51)

* int:                                   Working with hash algorithms.

                                                              (line 184)







Tag Table:

Node: Top730

Node: Introduction6207

Node: Getting Started6581

Node: Features7464

Node: Overview8254

Node: Preparation8902

Node: Header9700

Node: Building sources10583

Node: Building sources using Automake12505

Node: Initializing the library13686

Node: Multi Threading14729

Ref: Multi Threading-Footnote-118634

Node: Generalities19042

Node: Controlling the library19367

Node: Modules19751

Node: Error Handling20530

Node: Error Values23055

Node: Error Sources27995

Node: Error Codes30266

Node: Error Strings33227

Node: Handler Functions34379

Node: Progress handler34938

Node: Allocation handler36885

Node: Error handler38180

Node: Logging handler39237

Node: Symmetric cryptography39743

Node: Available ciphers40532

Node: Cipher modules42436

Node: Available cipher modes46959

Node: Working with cipher handles47638

Node: General cipher functions55498

Node: Hashing57975

Node: Available hash algorithms58781

Node: Hash algorithm modules60808

Node: Working with hash algorithms64655

Node: Public Key cryptography (I)75048

Node: Available algorithms75901

Node: Used S-expressions76254

Node: Public key modules78046

Node: Cryptographic Functions83634

Node: General public-key related Functions91123

Node: Public Key cryptography (II)98345

Node: Available asymmetric algorithms99252

Node: Working with sets of data99932

Node: Working with handles102954

Node: Working with keys103898

Node: Using cryptographic functions107960

Node: Handle-independent functions109778

Node: Random Numbers110392

Node: Quality of random numbers110687

Node: Retrieving random numbers111343

Node: S-expressions112755

Node: Data types for S-expressions113399

Node: Working with S-expressions113725

Node: MPI library122259

Node: Data types123567

Node: Basic functions123773

Node: MPI formats125841

Node: Calculations128631

Node: Comparisons130886

Node: Bit manipulations131504

Node: Miscellaneous132648

Node: Utilities134492

Node: Memory allocation134696

Node: Library Copying135952

Node: Copying164116

Node: Concept Index183319

Node: Function and Data Index184274



End Tag Table