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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 m…

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