/indra/libgcrypt/libgcrypt-1.2.2/doc/gcrypt.texi

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\input texinfo                  @c -*- Texinfo -*-

@c %**start of header

@setfilename gcrypt.info

@include version.texi

@settitle The Libgcrypt Reference Manual

@c Unify some of the indices.

@syncodeindex tp fn

@syncodeindex pg fn

@c %**end of header

@copying

This manual is for Libgcrypt

(version @value{VERSION}, @value{UPDATED}),

which is GNU's library of cryptographic building blocks.



Copyright @copyright{} 2000, 2002, 2003, 2004 Free Software Foundation, Inc.



@quotation

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''.

@end quotation

@end copying



@dircategory GNU Libraries

@direntry

* libgcrypt: (gcrypt).  Cryptographic function library.

@end direntry







@c

@c Titlepage

@c

@setchapternewpage odd

@titlepage

@title The Libgcrypt Reference Manual

@subtitle Version @value{VERSION}

@subtitle @value{UPDATED}

@author Werner Koch (@email{wk@@gnupg.org})

@author Moritz Schulte (@email{mo@@g10code.com})



@page

@vskip 0pt plus 1filll

@insertcopying

@end titlepage





@summarycontents

@contents

@page





@ifnottex

@node Top

@top The Libgcrypt Library

@insertcopying

@end ifnottex





@menu

* Introduction::                 What is @acronym{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.



@detailmenu

 --- The Detailed Node Listing ---



Introduction

* Getting Started::             How to use this manual.

* Features::                    A glance at @acronym{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 @acronym{Libgcrypt} can be used in a MT environment.



Generalities

* Controlling the library::     Controlling @acronym{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::   @acronym{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.



@end detailmenu



@end menu







@c **********************************************************

@c *******************  Introduction  ***********************

@c **********************************************************

@node Introduction

@chapter Introduction

`@acronym{Libgcrypt}' is a library providing cryptographic building blocks.



@menu

* Getting Started::             How to use this manual.

* Features::                    A glance at @acronym{Libgcrypt}'s features.

* Overview::                    Overview about the library.

@end menu



@node Getting Started

@section Getting Started



This manual documents the `@acronym{Libgcrypt}' library application programming

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

are explained.



@noindent

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.





@node Features

@section Features



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

a similar job.



@table @asis

@item It's Free Software

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

Lesser General Public License (@pxref{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

(@pxref{Copying}); please see the README file of the distribution for of

list of these parts.



@item It encapsulates the low level cryptography

`@acronym{Libgcrypt}' provides a high level interface to cryptographic building

blocks using an extendable and flexible API.



@end table



@node Overview

@section Overview



@noindent

The `@acronym{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.



@acronym{Libgcrypt} depends on the library `libgpg-error', which

contains common error handling related code for GnuPG components.



@c **********************************************************

@c *******************  Preparation  ************************

@c **********************************************************

@node Preparation

@chapter Preparation



To use `@acronym{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 @acronym{Libgcrypt} can be used in a MT environment.

@end menu





@node Header

@section 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:



@example

#include <gcrypt.h>

@end example



The name space of `@acronym{Libgcrypt}' is @code{gcry_*} for function

and type names and @code{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 @acronym{Libgcrypt} uses

libgpg-error, which uses @code{gpg_err_*} as name space for function

and type names and @code{GPG_ERR_*} for other symbols, including all

the error codes.



@node Building sources

@section 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 @option{-I} option).



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

source is configured.  To solve this problem, `@acronym{Libgcrypt}' ships with a small

helper program @command{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 @option{--cflags} option to @command{libgcrypt-config}.  The following

example shows how it can be used at the command line:



@example

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

@end example



Adding the output of @samp{libgcrypt-config --cflags} to the compilers

command line will ensure that the compiler can find the `@acronym{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 @option{-L} option).  For this, the option @option{--libs} to

@command{libgcrypt-config} can be used.  For convenience, this option

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

with the `@acronym{Libgcrypt}' libraries (in particular, the @samp{-lgcrypt}

option).  The example shows how to link @file{foo.o} with the `@acronym{Libgcrypt}'

library to a program @command{foo}.



@example

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

@end example



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

specifying both options to @command{libgcrypt-config}:



@example

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

@end example



@node Building sources using Automake

@section 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 @command{libgcrypt-config} script at all.

@acronym{Libgcrypt} provides an extension to Automake that does all

the work for you.



@c A simple macro for optional variables.

@macro ovar{varname}

@r{[}@var{\varname\}@r{]}

@end macro

@defmac AM_PATH_LIBGCRYPT (@ovar{minimum-version}, @ovar{action-if-found}, @ovar{action-if-not-found})

Check whether @acronym{Libgcrypt} (at least version

@var{minimum-version}, if given) exists on the host system.  If it is

found, execute @var{action-if-found}, otherwise do

@var{action-if-not-found}, if given.



Additionally, the function defines @code{LIBGCRYPT_CFLAGS} to the

flags needed for compilation of the program to find the

@file{gcrypt.h} header file, and @code{LIBGCRYPT_LIBS} to the linker

flags needed to link the program to the @acronym{Libgcrypt} library.

@end defmac



You can use the defined Autoconf variables like this in your

@file{Makefile.am}:



@example

AM_CPPFLAGS = $(LIBGCRYPT_CFLAGS)

LDADD = $(LIBGCRYPT_LIBS)

@end example



@node Initializing the library

@section Initializing the library



It is often desirable to check that the version of `@acronym{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.



@deftypefun const char *gcry_check_version (const char *@var{req_version})



The function @code{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 @acronym{Libgcrypt}.

@end deftypefun



@node Multi Threading

@section Multi Threading



As mentioned earlier, the `@acronym{Libgcrypt}' library is 

thread-safe if you adhere to the following requirements:



@itemize @bullet

@item

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

callbacks with the @code{GCRYCTL_SET_THREAD_CBS} command

@strong{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.



@item

The function @code{gcry_check_version} must be called before any other

function in the library, except the @code{GCRYCTL_SET_THREAD_CBS}

command (called via the @code{gcry_control} function), because it

initializes the thread support subsystem in @acronym{Libgcrypt}.  To

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

memory with respect to other threads that also want to use

@acronym{Libgcrypt}.  For this, it is sufficient to call

@code{gcry_check_version} before creating the other threads using

@acronym{Libgcrypt}@footnote{At least this is true for POSIX threads,

as @code{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.}.



@item



As with the function @code{gpg_strerror}, @code{gcry_strerror} is not

thread safe.  You have to use @code{gpg_strerror_r} instead.

@end itemize





@acronym{Libgcrypt} contains convenient macros, which define the

necessary thread callbacks for PThread and for GNU Pth:



@table @code

@item 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''.



@item 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''.

@end table



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.



@c **********************************************************

@c *******************  General  ****************************

@c **********************************************************

@node Generalities

@chapter Generalities



@menu

* Controlling the library::     Controlling @acronym{Libgcrypt}'s behavior.

* Modules::                     Description of extension modules.

* Error Handling::              Error codes and such.

@end menu



@node Controlling the library

@section Controlling the library



@deftypefun gcry_error_t gcry_control (enum gcry_ctl_cmds @var{cmd}, ...)



This function can be used to influence the general behavior of

@acronym{Libgcrypt} in several ways.  Depending on @var{cmd}, more

arguments can or have to be provided.



@end deftypefun



@node Modules

@section Modules



@acronym{Libgcrypt} supports the use of `extension modules', which

implement algorithms in addition to those already built into the

library directly.



@deftp {Data type} gcry_module_t

This data type represents a `module'.

@end deftp



Functions registering modules provided by the user take a `module

specification structure' as input and return a value of

@code{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

@acronym{Libgcrypt} until it is unregistered again.



@c **********************************************************

@c *******************  Errors  ****************************

@c **********************************************************

@node Error Handling

@section Error Handling



Many functions in @acronym{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.



@acronym{Libgcrypt} uses the @code{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, @acronym{Libgcrypt} does

not use its own identifiers for error codes, but uses those provided

by @code{libgpg-error}.  They usually start with @code{GPG_ERR_}.



However, @acronym{Libgcrypt} does provide aliases for the functions

defined in libgpg-error, which might be preferred for name space

consistency.





Most functions in @acronym{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.

@end menu





@node Error Values

@subsection Error Values

@cindex error values

@cindex error codes

@cindex error sources



@deftp {Data type} {gcry_err_code_t}

The @code{gcry_err_code_t} type is an alias for the

@code{libgpg-error} type @code{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.

@end deftp



@deftp {Data type} {gcry_err_source_t}

The @code{gcry_err_source_t} type is an alias for the

@code{libgpg-error} type @code{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.

@end deftp



@deftp {Data type} {gcry_error_t}

The @code{gcry_error_t} type is an alias for the @code{libgpg-error}

type @code{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

(@code{GPG_ERR_NO_ERROR}), and that in this case all other parts of

the error value are set to 0, too.



Note that in @acronym{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.

@end deftp



@deftypefun {gcry_err_code_t} gcry_err_code (@w{gcry_error_t @var{err}})

The static inline function @code{gcry_err_code} returns the

@code{gcry_err_code_t} component of the error value @var{err}.  This

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

order to compare it with the @code{GPG_ERR_*} error code macros.

@end deftypefun



@deftypefun {gcry_err_source_t} gcry_err_source (@w{gcry_error_t @var{err}})

The static inline function @code{gcry_err_source} returns the

@code{gcry_err_source_t} component of the error value @var{err}.  This

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

order to compare it with the @code{GPG_ERR_SOURCE_*} error source macros.

@end deftypefun



@deftypefun {gcry_error_t} gcry_err_make (@w{gcry_err_source_t @var{source}}, @w{gcry_err_code_t @var{code}})

The static inline function @code{gcry_err_make} returns the error

value consisting of the error source @var{source} and the error code

@var{code}.



This function can be used in callback functions to construct an error

value to return it to the library.

@end deftypefun



@deftypefun {gcry_error_t} gcry_error (@w{gcry_err_code_t @var{code}})

The static inline function @code{gcry_error} returns the error value

consisting of the default error source and the error code @var{code}.



For @acronym{GCRY} applications, the default error source is

@code{GPG_ERR_SOURCE_USER_1}.  You can define

@code{GCRY_ERR_SOURCE_DEFAULT} before including @file{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.

@end deftypefun



The @code{libgpg-error} library provides error codes for all system

error numbers it knows about.  If @var{err} is an unknown error

number, the error code @code{GPG_ERR_UNKNOWN_ERRNO} is used.  The

following functions can be used to construct error values from system

errno numbers.



@deftypefun {gcry_error_t} gcry_err_make_from_errno (@w{gcry_err_source_t @var{source}}, @w{int @var{err}})

The function @code{gcry_err_make_from_errno} is like

@code{gcry_err_make}, but it takes a system error like @code{errno}

instead of a @code{gcry_err_code_t} error code.

@end deftypefun



@deftypefun {gcry_error_t} gcry_error_from_errno (@w{int @var{err}})

The function @code{gcry_error_from_errno} is like @code{gcry_error},

but it takes a system error like @code{errno} instead of a

@code{gcry_err_code_t} error code.

@end deftypefun



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.



@deftypefun {gcry_err_code_t} gcry_err_code_from_errno (@w{int @var{err}})

The function @code{gcry_err_code_from_errno} returns the error code

for the system error @var{err}.  If @var{err} is not a known system

error, the function returns @code{GPG_ERR_UNKNOWN_ERRNO}.

@end deftypefun



@deftypefun {int} gcry_err_code_to_errno (@w{gcry_err_code_t @var{err}})

The function @code{gcry_err_code_to_errno} returns the system error

for the error code @var{err}.  If @var{err} is not an error code

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

this system, the function returns @code{0}.

@end deftypefun





@node Error Sources

@subsection Error Sources

@cindex error codes, list of



The library @code{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 @code{0}, the whole error

value will be @code{0}.  In this case the error source part is of

course @code{GPG_ERR_SOURCE_UNKNOWN}.



The list of error sources that might occur in applications using

@acronym{Libgctypt} is:



@table @code

@item GPG_ERR_SOURCE_UNKNOWN

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

@code{0}.



@item GPG_ERR_SOURCE_GPGME

The error source is @acronym{GPGME} itself.



@item GPG_ERR_SOURCE_GPG

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

OpenPGP protocol.



@item GPG_ERR_SOURCE_GPGSM

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

OpenPGP protocol.



@item GPG_ERR_SOURCE_GCRYPT

The error source is @code{libgcrypt}, which is used by crypto engines

to perform cryptographic operations.



@item GPG_ERR_SOURCE_GPGAGENT

The error source is @command{gpg-agent}, which is used by crypto

engines to perform operations with the secret key.



@item GPG_ERR_SOURCE_PINENTRY

The error source is @command{pinentry}, which is used by

@command{gpg-agent} to query the passphrase to unlock a secret key.



@item GPG_ERR_SOURCE_SCD

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

@command{gpg-agent} to delegate operations with the secret key to a

SmartCard.



@item GPG_ERR_SOURCE_KEYBOX

The error source is @code{libkbx}, a library used by the crypto

engines to manage local keyrings.



@item GPG_ERR_SOURCE_USER_1

@item GPG_ERR_SOURCE_USER_2

@item GPG_ERR_SOURCE_USER_3

@item 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

@acronym{Libgcrypt} can use them to mark error values coming from callback

handlers.  Thus @code{GPG_ERR_SOURCE_USER_1} is the default for errors

created with @code{gcry_error} and @code{gcry_error_from_errno},

unless you define @code{GCRY_ERR_SOURCE_DEFAULT} before including

@file{gcrypt.h}.

@end table





@node Error Codes

@subsection Error Codes

@cindex error codes, list of



The library @code{libgpg-error} defines many error values.  The

following list includes the most important error codes.



@table @code

@item GPG_ERR_EOF

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



@item GPG_ERR_NO_ERROR

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

@code{0}.  Also, it is guaranteed that an error value made from the

error code @code{0} will be @code{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.



@item 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.



@item GPG_ERR_ENOMEM

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



@item GPG_ERR_E...

System errors are mapped to GPG_ERR_EFOO where FOO is the symbol for

the system error.



@item GPG_ERR_INV_VALUE

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



@item GPG_ERR_UNUSABLE_PUBKEY

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



@item GPG_ERR_UNUSABLE_SECKEY

This value means that some signers were invalid.



@item GPG_ERR_NO_DATA

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



@item GPG_ERR_CONFLICT

This value means that a conflict of some sort occurred.



@item 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.



@item GPG_ERR_DECRYPT_FAILED

This value indicates that a decryption operation was unsuccessful.



@item GPG_ERR_WRONG_KEY_USAGE

This value indicates that a key is not used appropriately.



@item GPG_ERR_NO_SECKEY

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



@item GPG_ERR_UNSUPPORTED_ALGORITHM

This value means a verification failed because the cryptographic

algorithm is not supported by the crypto backend.



@item GPG_ERR_BAD_SIGNATURE

This value means a verification failed because the signature is bad.



@item GPG_ERR_NO_PUBKEY

This value means a verification failed because the public key is not

available.



@item GPG_ERR_USER_1

@item GPG_ERR_USER_2

@item ...

@item GPG_ERR_USER_16

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

freely used by other software.  Applications using @acronym{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.

@end table





@node Error Strings

@subsection Error Strings

@cindex error values, printing of

@cindex error codes, printing of

@cindex error sources, printing of

@cindex error strings



@deftypefun {const char *} gcry_strerror (@w{gcry_error_t @var{err}})

The function @code{gcry_strerror} returns a pointer to a statically

allocated string containing a description of the error code contained

in the error value @var{err}.  This string can be used to output a

diagnostic message to the user.

@end deftypefun





@deftypefun {const char *} gcry_strsource (@w{gcry_error_t @var{err}})

The function @code{gcry_strerror} returns a pointer to a statically

allocated string containing a description of the error source

contained in the error value @var{err}.  This string can be used to

output a diagnostic message to the user.

@end deftypefun



The following example illustrates the use of the functions described

above:



@example

@{

  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));

    @}

@}

@end example



@c **********************************************************

@c *******************  General  ****************************

@c **********************************************************

@node Handler Functions

@chapter Handler Functions



@acronym{Libgcrypt} makes it possible to install so called `handler functions',

which get called by @acronym{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.

@end menu



@node Progress handler

@section Progress handler



It is often useful to retrieve some feedback while long running

operations are performed.



@deftp {Data type} gcry_handler_progress_t

Progress handler functions have to be of the type

@code{gcry_handler_progress_t}, which is defined as:



@code{void (*gcry_handler_progress_t) (void *, const char *, int, int, int)}

@end deftp



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

this purpose.



@deftypefun void gcry_set_progress_handler (gcry_handler_progress_t @var{cb}, void *@var{cb_data})



This function installs @var{cb} as the `Progress handler' function.

@var{cb} must be defined as follows:



@example

void

my_progress_handler (void *@var{cb_data}, const char *@var{what},

                     int @var{printchar}, int @var{current}, int @var{total})

@{

  /* Do something.  */

@}

@end example



A description of the arguments of the progress handler function follows.



@table @var

@item cb_data

The argument provided in the call to @code{gcry_set_progress_handler}.

@item what

A string identifying the type of the progress output.  The following

values for @var{what} are defined:



@table @code

@item need_entropy

Not enough entropy is available.  @var{total} holds the number of

required bytes.



@item primegen

Values for @var{printchar}:

@table @code

@item \n

Prime generated.

@item !

Need to refresh the pool of prime numbers.

@item <, >

Number of bits adjusted.

@item ^

Searching for a generator.

@item .

Fermat test on 10 candidates failed.

@item :

Restart with a new random value.

@item +

Rabin Miller test passed.

@end table



@end table



@end table

@end deftypefun



@node Allocation handler

@section Allocation handler



It is possible to make @acronym{Libgcrypt} use special memory

allocation functions instead of the built-in ones.



Memory allocation functions are of the following types:

@deftp {Data type} gcry_handler_alloc_t

This type is defined as: @code{void *(*gcry_handler_alloc_t) (size_t n)}.

@end deftp

@deftp {Data type} gcry_handler_secure_check_t

This type is defined as: @code{int *(*gcry_handler_secure_check_t) (const void *)}.

@end deftp

@deftp {Data type} gcry_handler_realloc_t

This type is defined as: @code{void *(*gcry_handler_realloc_t) (void *p, size_t n)}.

@end deftp

@deftp {Data type} gcry_handler_free_t

This type is defined as: @code{void *(*gcry_handler_free_t) (void *)}.

@end deftp



Special memory allocation functions can be installed with the

following function:



@deftypefun void gcry_set_allocation_handler (gcry_handler_alloc_t @var{func_alloc}, gcry_handler_alloc_t @var{func_alloc_secure}, gcry_handler_secure_check_t @var{func_secure_check}, gcry_handler_realloc_t @var{func_realloc}, gcry_handler_free_t @var{func_free})

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

functions for doing memory allocation.

@end deftypefun



@node Error handler

@section Error handler



The following functions may be used to register handler functions that

are called by @acronym{Libgcrypt} in case certain error conditions

occur.



@deftp {Data type} gcry_handler_no_mem_t

This type is defined as: @code{void (*gcry_handler_no_mem_t) (void *, size_t, unsigned int)}

@end deftp

@deftypefun void gcry_set_outofcore_handler (gcry_handler_no_mem_t @var{func_no_mem}, void *@var{cb_data})

This function registers @var{func_no_mem} as `out-of-core handler',

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

memory available.

@end deftypefun



@deftp {Data type} gcry_handler_error_t

This type is defined as: @code{void (*gcry_handler_error_t) (void *, int, const char *)}

@end deftp



@deftypefun void gcry_set_fatalerror_handler (gcry_handler_error_t @var{func_error}, void *@var{cb_data})

This function registers @var{func_error} as `error handler',

which means that it will be called in error conditions.

@end deftypefun



@node Logging handler

@section Logging handler



@deftp {Data type} gcry_handler_log_t

This type is defined as: @code{void (*gcry_handler_log_t) (void *, int, const char *, va_list)}

@end deftp



@deftypefun void gcry_set_log_handler (gcry_handler_log_t @var{func_log}, void *@var{cb_data})

This function registers @var{func_log} as `logging handler', which

means that it will be called in case @acronym{Libgcrypt} wants to log

a message.

@end deftypefun



@c **********************************************************

@c *******************  Ciphers  ****************************

@c **********************************************************

@c @include cipher-ref.texi

@node Symmetric cryptography

@chapter 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 @acronym{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.

@end menu



@node Available ciphers

@section Available ciphers



@table @code

@item GCRY_CIPHER_NONE

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

The value always evaluates to false.



@item 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.



@item 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.



@item GCRY_CIPHER_CAST5

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

	

@item GCRY_CIPHER_BLOWFISH

The blowfish algorithm. The current implementation allows only for a key

size of 128 bits.



@item GCRY_CIPHER_SAFER_SK128

Reserved and not currently implemented.



@item GCRY_CIPHER_DES_SK	  

Reserved and not currently implemented.

 

@item  GCRY_CIPHER_AES        

@itemx GCRY_CIPHER_AES128

@itemx GCRY_CIPHER_RIJNDAEL

@itemx GCRY_CIPHER_RIJNDAEL128

AES (Rijndael) with a 128 bit key.



@item  GCRY_CIPHER_AES192     

@itemx GCRY_CIPHER_RIJNDAEL128

AES (Rijndael) with a 192 bit key.



@item  GCRY_CIPHER_AES256 

@itemx GCRY_CIPHER_RIJNDAEL256

AES (Rijndael) with a 256 bit key.

    

@item  GCRY_CIPHER_TWOFISH

The Twofish algorithm with a 256 bit key.

    

@item  GCRY_CIPHER_TWOFISH128

The Twofish algorithm with a 128 bit key.

    

@item  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. 



@item  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.



@end table



@node Cipher modules

@section Cipher modules



@acronym{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 @xref{Modules}.



@deftp {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:



@table @code

@item const char *name

The primary name of the algorithm.

@item const char **aliases

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

be terminated with a NULL element.

@item 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.

@item size_t blocksize

The block size of the algorithm, in bytes.

@item size_t keylen

The length of the key, in bits.

@item size_t contextsize

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

for each handle.

@item gcry_cipher_setkey_t setkey

The function responsible for initializing a handle with a provided

key.  See below for a description of this type.

@item gcry_cipher_encrypt_t encrypt

The function responsible for encrypting a single block.  See below for

a description of this type.

@item gcry_cipher_decrypt_t decrypt

The function responsible for decrypting a single block.  See below for

a description of this type.

@item gcry_cipher_stencrypt_t stencrypt

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

this type.

@item gcry_cipher_stdecrypt_t stdecrypt

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

this type.

@end table

@end deftp



@deftp {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:

@table @code

@item const char *oid

Textual representation of the OID.

@item int mode

Cipher mode for which this OID is valid.

@end table

@end deftp



@deftp {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)

@end deftp



@deftp {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)

@end deftp



@deftp {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)

@end deftp



@deftp {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)

@end deftp



@deftp {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)

@end deftp



@deftypefun gcry_error_t gcry_cipher_register (gcry_cipher_spec_t *@var{cipher}, unsigned int *algorithm_id, gcry_module_t *@var{module})



Register a new cipher module whose specification can be found in

@var{cipher}.  On success, a new algorithm ID is stored in

@var{algorithm_id} and a pointer representing this module is stored

in @var{module}.

@end deftypefun



@deftypefun void gcry_cipher_unregister (gcry_module_t @var{module})

Unregister the cipher identified by @var{module}, which must have been

registered with gcry_cipher_register.

@end deftypefun



@deftypefun gcry_error_t gcry_cipher_list (int *@var{list}, int *@var{list_length})

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

@var{list} is zero, write the number of loaded cipher modules to

@var{list_length} and return.  If @var{list} is non-zero, the first

*@var{list_length} algorithm IDs are stored in @var{list}, which must

be of according size.  In case there are less cipher modules than

*@var{list_length}, *@var{list_length} is updated to the correct

number.

@end deftypefun



@node Available cipher modes

@section Available cipher modes



@table @code

@item GCRY_CIPHER_MODE_NONE

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

of this constant is always 0.



@item GCRY_CIPHER_MODE_ECB

Electronic Codebook mode.  



@item GCRY_CIPHER_MODE_CFB

Cipher Feedback mode.



@item  GCRY_CIPHER_MODE_CBC

Cipher Block Chaining mode.



@item GCRY_CIPHER_MODE_STREAM

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



@item GCRY_CIPHER_MODE_OFB

Outer Feedback mode.



@item  GCRY_CIPHER_MODE_CTR

Counter mode.



@end table



@node Working with cipher handles

@section 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:



@deftypefun gcry_error_t gcry_cipher_open (gcry_cipher_hd_t *@var{hd}, int @var{algo}, int @var{mode}, unsigned int @var{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 @var{algo}.  See

@xref{Available ciphers}, for a list of supported ciphers and the

according constants.



Besides using the constants directly, the function

@code{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 @var{mode}.  See

@xref{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 @var{flags} can either be passed as @code{0} or as

the bit-wise OR of the following constants.



@table @code

@item GCRY_CIPHER_SECURE

Make sure that all operations are allocated in secure memory.  This is

useful, when the key material is highly confidential.

@item GCRY_CIPHER_ENABLE_SYNC

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

@acronym{Libgcrypt}'s CFB mode implementation to allow for OpenPGP's CFB variant. 

See @code{gcry_cipher_sync}.

@i…

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