\input texinfo @c -*- Texinfo -*-
@c Copyright (C) 2000, 2002, 2003 Free Software Foundation, Inc.
@c
@c This file is part of the Libgcrypt.
@c
@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.1 or
@c any later version published by the Free Software Foundation; with no
@c Invariant Sections, with no the Front-Cover texts, and with no
@c Back-Cover Texts.
@c A copy of the license is included in the file 'fdl.texi'.
@c
@setfilename gcrypt.info
@settitle The `Libgcrypt' Reference Manual
@dircategory GNU Libraries
@direntry
* libgcrypt: (gcrypt) Cryptographic function library.
@end direntry
@include version.texi
@c Unify some of the indices.
@syncodeindex tp fn
@syncodeindex pg fn
@ifinfo
This file documents the `Libgcrypt' library.
This is Edition @value{EDITION}, last updated @value{UPDATED}, of
@cite{The `Libgcrypt' Reference Manual}, for Version
@value{VERSION}.
Copyright @copyright{} 2000, 2002, 2003 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no the Front-Cover texts, and with no
Back-Cover Texts. A copy of the license is included in the section
entitled ``GNU Free Documentation License''.
@end ifinfo
@c @iftex
@c @shorttitlepage The `Libgcrypt' Reference Manual
@c @end iftex
@titlepage
@center @titlefont{The `Libgcrypt'}
@sp 1
@center @titlefont{Reference Manual}
@sp 6
@center Edition @value{EDITION}
@sp 1
@center last updated @value{UPDATED}
@sp 1
@center for version @value{VERSION}
@page
@vskip 0pt plus 1filll
Copyright @copyright{} 2000, 2002, 2003 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no the Front-Cover texts, and with no
Back-Cover Texts. A copy of the license is included in the section
entitled ``GNU Free Documentation License''.
@end titlepage
@page
@ifnottex
@node Top
@top Main Menu
This is Edition @value{EDITION}, last updated @value{UPDATED}, of
@cite{The `Libgcrypt' Reference Manual}, for Version
@value{VERSION} of the @acronym{GPGME} library.
@end ifnottex
@menu
* Introduction:: How to use this manual.
* Preparation:: What you should do before using the library.
* Cipher Functions:: All about ciphers.
* Hash Functions:: How to use cryptographic hash functions.
* Public Key Functions:: How to use asymmetric encryption.
* Random Numbers:: How to create random.
* S-expressions:: How to manage S-expressions.
* MPI Functions:: How to work with big integers.
* Utilities:: Helper functions.
* Error Handling:: Error codes and such.
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'.
* Free Documentation License:: This manual is under the GNU Free
Documentation License.
Indices
* Concept Index:: Index of concepts and programs.
* Function and Data Index:: Index of functions, variables and data types.
@detailmenu
@end detailmenu
@end menu
@c **********************************************************
@c ******************* Introduction ***********************
@c **********************************************************
@node Introduction
@chapter Introduction
`Libgcrypt' is a library to provide cryptographic building blocks.
@menu
* Getting Started::
* Features::
* Overview::
@end menu
@node Getting Started
@section Getting Started
This manual documents the `Libgcrypt' library programming interface.
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.
@node Features
@section Features
@noindent
`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
`Libgcrypt' a high level interface to cryptographic building blocks
using an extendable and flexible API.
@end table
@node Overview
@section Overview
@noindent
The `Libgcrypt' library is thread-safe. Well, we hope so ;-). Frankly,
@code{gcry_errno} is not yet thread-safe. Most others are believed to
be. Libgcrypt automagically detects whether an applications uses no
threading, pthreads or GNU Pth.
@c **********************************************************
@c ******************* Preparation ************************
@c **********************************************************
@node Preparation
@chapter 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::
* Version Check::
* Building the source::
@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 programs
using the library, either directly or through some other header file,
like this:
@example
#include <gcrypt.h>
@end example
The name space of `Libgcrypt' is @code{gcry_*} for function names,
@code{Gcry*} for data types 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.
@node Version Check
@section Version Check
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.
@deftypefun const char *gcry_check_version (const char *@var{req_version})
Check that the the version of the library is at minimum the one given as
a string in @var{req_version} and return the actual version string of
the library; return NULL if the condition is not met. If @code{NULL} is
passed to this function no check is done and only the version string is
returned. It is a pretty good idea to run this function as soon as
possible, because it may also initializes some subsystems. In a
multi-threaded environment if should be called before any more threads
are created.
@end deftypefun
@node Building the source
@section Building the source
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, `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 `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 `Libgcrypt' libraries (in particular, the @samp{-lgcrypt}
option). The example shows how to link @file{foo.o} with the `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
@c **********************************************************
@c ******************* Ciphers ****************************
@c **********************************************************
@c @include cipher-ref.texi
@node Cipher Functions
@chapter Cipher Functions
The cipher functions are used for symmetrical encryption,
i.e. encryption using a shared key. The programming model follows an
open/process/close paradigm and in that similar to the other building
blocks provided by Libgcrypt.
To use a cipher algorithm, you must first allocate an handle for
this. This can is to be done using the open function:
@deftypefun GcryCipherHd gcry_cipher_open (int @var{algo}, int @var{mode}, unsigned int @var{flags})
This function creates the context required for most of the other cipher
functions and returns a handle to it. In case of an error @code{NULL}
is returned. You must tell this function which algorithm and what mode
you want to use. The function @code{gcry_cipher_map_name} may be used to
get the a value for the @var{algo} from a textual name or one of the
predefined constants can be used:
@c begin cipher algorithm constants
@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_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 is can be broken in reasonable time using a brute force approach.
@end table
@c end cipher algorithm constants
@c begin cipher modes constants
The second argument is @var{mode} which describes the mode the algorithm
is to be used in. Note, that some modes don't work together with
all algorithms. The following modes are available:
@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.
@end table
@c end cipher modes constants
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
Libgcrypt's CFB mode implementation to allow for OpenPGP's CFB variant.
See @code{gcry_cipher_sync}.
@item GCRY_CIPHER_CBC_CTS
Enable cipher text stealing for the CBS mode.
@end table
@end deftypefun
@c end gcry_cipher_open
To release the context allocated with this function,
@code{gcry_cipher_close} should be used:
@deftypefun void gcry_cipher_close (GcryCipherHd @var{h})
This function releases the context created by @code{gcry_cipher_open}.
@end deftypefun
Now that a context has been allocated, the key to be used for decryption
or encryption must be set. This is done with the following function:
@deftypefun int gcry_cipher_setkey (GcryCipherHd @var{h}, void *@var{k}, size_t @var{l})
Set the key @var{k} used for encryption or decryption in the context
denoted by the handle @var{h}. The length @var{l} of the key @var{k}
must match the required length of the algorithm set for this context or
be in the allowed range for algorithms with variable key size. The
function checks this and returns an error if there is a problem. A
caller should always check for an error.
Note, this is currently implemented as a
macro but may be changed to a function in the future.
@end deftypefun
Most crypto modes requires an initialization vector (IV), which usually
is a non-secret random string acting as a kind of salt value. To set
this IV, use the function:
@deftypefun int gcry_cipher_setiv (GCRY_CIPHER_HD @var{h}, void *@var{k}, size_t @var{l})
Set the initialization vector used for encryption or decryption. The
vector is passed as the buffer @var{K} of length @var{l} and copied to
internal data structures. The function checks that the IV matches the
requirement of the selected algorithm and mode. Note, that this is
implemented as a macro.
@end deftypefun
The actual encryption and decryption is done by using one of the
following functions. They may be used as often as required to process
all the data.
@deftypefun int gcry_cipher_encrypt (GCRY_CIPHER_HD @var{h}, unsigned char *{out}, size_t @var{outsize}, const unsigned char *@var{in}, size_t @var{inlen})
@code{gcry_cipher_encrypt} is used to encrypt the data. This function
can either work in place or with two buffers. It uses the cipher
context already setup and described by the handle @var{h}. There are 2
ways to use the function: If @var{in} is passed as @code{NULL} and
@var{inlen} is @code{0}, in-place encryption of the data in @var{out} or
length @var{outsize} takes place. With @var{in} being not @code{NULL},
@var{inlen} bytes are encrypted to the buffer @var{out} which must have
at least a size of @var{inlen}. @var{outlen} must be set to the
allocated size of @var{out}, so that the function can check that there
is sufficient space. Note, that overlapping buffers are not allowed.
Depending on the selected algorithms and encryption mode, the length of
the buffers must be a multiple of the block size.
The function returns @code{0} on success or an error code.
@end deftypefun
@deftypefun int gcry_cipher_decrypt (GCRY_CIPHER_HD @var{h}, unsigned char *{out}, size_t @var{outsize}, const unsigned char *@var{in}, size_t @var{inlen})
@code{gcry_cipher_decrypt} is used to decrypt the data. This function
can either work in place or with two buffers. It uses the cipher
context already setup and described by the handle @var{h}. There are 2
ways to use the function: If @var{in} is passed as @code{NULL} and
@var{inlen} is @code{0}, in-place decryption of the data in @var{out} or
length @var{outsize} takes place. With @var{in} being not @code{NULL},
@var{inlen} bytes are decrypted to the buffer @var{out} which must have
at least a size of @var{inlen}. @var{outlen} must be set to the
allocated size of @var{out}, so that the function can check that there
is sufficient space. Note, that overlapping buffers are not allowed.
Depending on the selected algorithms and encryption mode, the length of
the buffers must be a multiple of the block size.
The function returns @code{0} on success or an error code.
@end deftypefun
OpenPGP (as defined in RFC-2440) requires a special sync operation in
some places, the following function is used for this:
@deftypefun int gcry_cipher_sync (GCRY_CIPHER_HD @var{h})
Perform the OpenPGP sync operation on context @var{h}. Note, that this
is a no-op unless the context was created with the flag
@code{GCRY_CIPHER_ENABLE_SYNC}
@end deftypefun
Some of the described functions are implemented as macros utilizing a
catch-all control function. This control function is rarely used
directly but there is nothing which would inhibit it:
@deftypefun int gcry_cipher_ctl (GCRY_CIPHER_HD @var{h}, int @var{cmd}, void *@var{buffer}, size_t @var{buflen})
@code{gcry_cipher_ctl} controls various aspects of the cipher module and
specific cipher contexts. Usually some more specialized functions or
macros are used for this purpose. The semantics of the function and its
parameters depends on the the command @var{cmd} and the passed context
handle @var{h}. Please see the comments in the source code
(@code{src/global.c}) for details.
@end deftypefun
@c ***********************************************
@c *********** cipher info ********************
@c ***********************************************
To work with the algorithms, several functions are available to map
algorithm names to the internal identifiers, as well as ways to retrieve
information about an algorithm or the current cipher context.
@deftypefun int gcry_cipher_info (GCRY_CIPHER_HD @var{h}, int @var{what}, void *@var{buffer}, size_t *@var{nbytes})
@code{gcry_cipher_info} is used to retrieve various
information about a cipher context or the cipher module in general.
Currently no information is available.
@end deftypefun
@deftypefun int gcry_cipher_algo_info (int @var{algo}, int @var{what}, void *@var{buffer}, size_t *@var{nbytes})
This function is used to retrieve information on a specific algorithm.
You pass the cipher algorithm ID as @var{algo} and the type of
information requested as @var{what}. The result is either returned as
the return code of the function or copied to the provided @var{buffer}
whose allocated length must be available in an integer variable with the
address passed in @var{nbytes}. This variable will also receive the
actual used length of the buffer.
The function returns @code{-1} on error; @code{gcry_errno} may be used
to get the actual error code.
Here is a list of supported codes for @var{what}:
@c begin constants for gcry_cipher_algo_info
@table @code
@item GCRYCTL_GET_KEYLEN:
Return the length of the key. If the algorithm supports multiple key
length, the maximum supported value is returned. The length is returned
as number of octets (bytes) and not as number of bits. @var{buffer} and
@var{nbytes} must be zero.
@item GCRYCTL_GET_BLKLEN:
Return the block length of the algorithm counted in octets.
@var{buffer} and @var{nbytes} must be zero.
@item GCRYCTL_TEST_ALGO:
Returns @code{0} when the specified algorithm is available for use.
@var{buffer} and @var{nbytes} must be zero.
@end table
@c end constants for gcry_cipher_algo_info
@end deftypefun
@c end gcry_cipher_algo_info
@deftypefun const char *gcry_cipher_algo_name (int @var{algo})
@code{gcry_cipher_algo_name} returns a string with the name of the
cipher algorithm @var{algo}. If the algorithm is not known or another
error occurred, an empty string is returned. This function will never
return @code{NULL}.
@end deftypefun
@deftypefun int gcry_cipher_map_name (const char *@var{name})
@code{gcry_cipher_map_name} returns the algorithm identifier for the
cipher algorithm described by the string @var{name}. If this algorithm
is not available @code{0} is returned.
@end deftypefun
@deftypefun int gcry_cipher_mode_from_oid (const char *@var{string})
Return the cipher mode associated with an @acronym{ASN.1} object
identifier. The object identifier is expected to be in the
@acronym{IETF}-style dotted decimal notation. The function returns
@code{0} for an unknown object identifier or when no mode is associated
with it.
@end deftypefun
@c **********************************************************
@c ******************* Hash Functions *********************
@c **********************************************************
@node Hash Functions
@chapter Hash Functions
How to use cryptographic hash functions. Libgcrypt provides an easy and
consistent to use interface to hash functions. Hashing is buffered and
several hash algorithms can be updated at once. It is possible to
calculate a MAC using the same routines.
For convenience reasons, we plan to integrate simple CRC algorithms too
To use most of these function it is necessary to create a context; this
is done using:
@deftypefun GcryMDHd gcry_md_open (int @var{algo}, unsigned int @var{flags})
Create a message digest object for algorithm @var{algo}. @var{flags}
may be given as an bitwise OR of constants described below. @var{algo}
may be given as @code{0} if the algorithms to use are later set using
@code{gcry_md_enable}.
The following algorithms are supported:
@c begin table of hash algorithms
@table @code
@item GCRY_MD_NONE
This is not a real algorithm but used by some functions as an error
return value. This constant is guaranteed to have the value @code{0}.
@item GCRY_MD_SHA1
This is the SHA-1 algorithm which yields a message digest of 20 bytes.
@item GCRY_MD_RMD160
This is the 160 bit version of the RIPE message digest (RIPE-MD-160).
Like SHA-1 it also yields a digest of 20 bytes.
@item GCRY_MD_MD5
This is the well known MD5 algorithm, which yields a message digest of
16 bytes.
@item GCRY_MD_MD4
This is the MD4 algorithm, which yields a message digest of 16 bytes.
@item GCRY_MD_MD2
This is an reserved identifier for MD-2; there is no implementation yet.
@item GCRY_MD_TIGER
This is the TIGER/192 algorithm which yields a message digest of 24 bytes.
@item GCRY_MD_HAVAL
This is an reserved for the HAVAL algorithm with 5 passes and 160
bit. It yields a message digest of 20 bytes. Note that there is no
implementation yet available.
@item GCRY_MD_SHA256
This is reserved for SHA-2 with 256 bits. It yields a message digest of
32 bytes. Note that there is no implementation yet available.
@item GCRY_MD_SHA384
This is reserved for SHA-2 with 384 bits. It yields a message digest of
48 bytes. Note that there is no implementation yet available.
@item GCRY_MD_SHA512
This is reserved for SHA-2 with 512 bits. It yields a message digest of
64 bytes. Note that there is no implementation yet available.
@end table
@c end table of hash algorithms
The flags allowed for @var{mode} are:
@c begin table of hash flags
@table @code
@item GCRY_MD_FLAG_SECURE
Allocate all buffers and the resulting digest in "secure memory". Use
this is the hashed data is highly confidential.
@item GCRY_MD_FLAG_HMAC
Turn the algorithm into a HMAC message authentication algorithm. Note
that the function @code{gcry_md_setkey} must be used set the MAC key.
@end table
@c begin table of hash flags
@end deftypefun
@c end function gcry_md_open
If you want to calculate several hash algorithms at the same time, you
have to use the following function right after the @code{gcry_md_open}:
@deftypefun int gcry_md_enable (GcryMDHd @var{h}, int @var{algo})
Add the message digest algorithm @var{algo} to the digest object
described by handle @var{h}. Duplicated enabling of algorithms is
detected and ignored.
@end deftypefun
If the flag @code{GCRY_MD_FLAG_HMAC} was used, the key for the MAC must
be set using the function:
@deftypefun int gcry_md_setkey (GcryMDHd @var{h}, const void *@var{key},
size_t @var{keylen})
For use with the HMAC feature, set the MAC key to the value of @var{key}
of length @var{keylen}.
@end deftypefun
After you are done with the hash calculation, you should release the
resources by using:
@deftypefun void gcry_md_close (GcryMDHd @var{h})
Release all resources of hash context @var{h}. @var{h} should not be
used after a call to this function. A @code{NULL} passed as @var{h} is
ignored.
@end deftypefun
Often you have to do several hash operations using the same algorithm.
To avoid the overhead of creating and releasing context, a reset function
is provided:
@deftypefun void gcry_md_reset (GcryMDHd @var{h})
Reset the current context to its initial state. This is effectively
identical to a close followed by an open and enabling all currently
active algorithms.
@end deftypefun
Often it is necessary to start hashing some data and than continue to
hash different data. To avoid hashing the same data several times (which
might not even be possible if the data is received from a pipe), a
snapshot of the current hash context can be taken and turned into a new
context:
@deftypefun GcryMDHd gcry_md_copy (GcryMDHd @var{h})
Create a new digest object as an exact copy of the object described by
handle @var{h}. The context is not reset and you can continue to hash
data using this context and independently using the original context.
@end deftypefun
Now that we have prepared everything to calculate hashes, its time to
see how it is actually done. There are 2 ways for this, one to
update the hash with a block of memory and one macro to update the hash
by just one character. Both may be used intermixed.
@deftypefun void gcry_md_write (GcryMDHd @var{h}, const void *@var{buffer}, size_t @var{length})
Pass @var{length} bytes of the data in @var{buffer} to the digest object
with handle @var{h} to update the digest values. This
function should be used for large blocks of data.
@end deftypefun
@deftypefun void gcry_md_putc (GcryMDHd @var{h}, int @var{c})
Pass the byte in @var{c} to the digest object with handle @var{h} to
update the digest value. This is an efficient function, implemented as
a macro to buffer the data before an actual update.
@end deftypefun
The semantics of the hash functions don't allow to read out intermediate
message digests because the calculation must be finalized fist. This
finalization may for example include the number of bytes hashed in the
message digest.
@deftypefun void gcry_md_final (GcryMDHd @var{h})
Finalize the message digest calculation. This is not really needed
because @code{gcry_md_read} does this implicitly. After this has been
done no further updates (by means of @code{gcry_md_write} or
@code{gcry_md_putc} are allowed. Only the first call to this function
has an effect. It is implemented as a macro.
@end deftypefun
The way to read out the calculated message digest is by using the
function:
@deftypefun unsigned char *gcry_md_read (GcryMDHd @var{h}, int @var{algo})
@code{gcry_md_read} returns the message digest after finalizing the
calculation. This function may be used as often as required but it will
always return the same value for one handle. The returned message digest
is allocated within the message context and therefore valid until the
handle is released or reseted (using @code{gcry_md_close} or
@code{gcry_md_reset}. @var{algo} may be given as 0 to return the only
enabled message digest or it may specify one of the enabled algorithms.
The function does return @code{NULL} if the requested algorithm has not
been enabled.
@end deftypefun
Because it is often necessary to get the message digest of one block of
memory, a fast convenience function is available for this task:
@deftypefun void gcry_md_hash_buffer (int @var{algo}, void *@var{digest}, const cvoid *@var{buffer}, size_t @var{length});
@code{gcry_md_hash_buffer} is a shortcut function to calculate a message
digest of a buffer. This function does not require a context and
immediately returns the message digest of the @var{length} bytes at
@var{buffer}. @var{digest} must be allocated by the caller, large
enough to hold the message digest yielded by the the specified algorithm
@var{algo}. This required size may be obtained by using the function
@code{gcry_md_get_algo_dlen}.
Note, that this function will abort the process if an unavailable
algorithm is used.
@end deftypefun
@c ***********************************
@c ***** MD info functions ***********
@c ***********************************
Hash algorithms are identified by internal algorithm numbers (see
@code{gcry_md_open} for a list. However, in most applications they are
used by names, so 2 functions are available to map between string
representations and hash algorithm identifiers.
@deftypefun const char *gcry_md_algo_name (int @var{algo})
Map the digest algorithm id @var{algo} to a string representation of the
algorithm name. For unknown algorithms this functions returns an
empty string. This function should not be used to test for the
availability of an algorithm.
@end deftypefun
@deftypefun int gcry_md_map_name (const char *@var{name})
Map the algorithm with @var{name} to a digest algorithm identifier.
Returns 0 if the algorithm name is not known. Names representing
@acronym{ASN.1} object identifiers are recognized if the @acronym{IETF}
dotted format is used and the OID is prefixed with either "@code{oid.}"
or "@code{OID.}". For a list of supported OIDs, see the source code at
@file{cipher/md.c}. This function should not be used to test for the
availability of an algorithm.
@end deftypefun
@deftypefun int gcry_md_get_asnoid (int @var{algo}, void *@var{buffer}, size_t *@var{length})
Return an DER encoded ASN.1 OID for the algorithm @var{algo} in the user
allocated @var{buffer}. @var{length} must point to variable with the
available size of @var{buffer} and receives after return the actual size
of the returned OID. The return value may be @code{GCRYERR_TOO_SHORT}
if the provided buffer is to short to receive the OID; it is possible to
call the function with @code{NULL} for @var{buffer} to have it only
return the required size. The function returns 0 on success.
@end deftypefun
To test whether an algorithm is actually available for use, the
following macro should be used:
@deftypefun int gcry_md_test_algo (int @var{algo})
The macro returns 0 if the algorithm @var{algo} is available for use.
@end deftypefun
If the length of a message digest is not known, it can be retrieved
using the following function:
@deftypefun unsigned int gcry_md_get_algo_dlen (int @var{algo})
Retrieve the length in bytes of the digest yielded by algorithm
@var{algo}. This is often used prior to @code{gcry_md_read} to allocate
sufficient memory for the digest.
@end deftypefun
In some situations it might be hard to remember the algorithm used for
the ongoing hashing. The following function might be used to get that
information:
@deftypefun int gcry_md_get_algo (GcryMDHd @var{h})
Retrieve the algorithm used with the handle @var{h}. Note, that this
does not work reliable if more than one algorithm is enabled in @var{h}.
@end deftypefun
The following macro might also be useful:
@deftypefun int gcry_md_is_secure (GcryMDHd @var{h})
This macro return true when the digest object @var{h} is allocated in "secure
memory"; i.e. @var{h} was created with the @code{GCRY_MD_FLAG_SECURE}.
@end deftypefun
Tracking bugs related to hashing is often a cumbersome task which
requires to add a lot of printf statements into the code. Libgcrypt
provides an easy way to avoid this. The actual data hashed can be
written to files on request. The following 2 macros should be used to
implement such a debugging facility:
@deftypefun void gcry_md_start_debug (GcryMDHd @var{h}, const char *@var{suffix})
Enable debugging for the digest object with handle @var{h}. This
creates create files named @file{dbgmd-<n>.<string>} while doing the
actual hashing. @var{suffix} is the string part in the filename. The
number is a counter incremented for each new hashing. The data in the
file is the raw data as passed to @code{gcry_md_write} or
@code{gcry_md_putc}.
@end deftypefun
@deftypefun void gcry_md_stop_debug (GcryMDHd @var{h}, int @var{reserved})
Stop debugging on handle @var{h}. @var{reserved} should be specified as
0. This function is usually not required because @code{gcry_md_close}
does implicitly stop debugging.
@end deftypefun
@c **********************************************************
@c ******************* Public Key *************************
@c **********************************************************
@node Public Key Functions
@chapter Public Key Functions
Public key encryption, also known as asymmetric encryption, is am easy
way for key management and to provide digital signatures. Libgcrypt
supports the RSA (Rivest-Shamir-Adleman) algorithms as well as DSA
(Digital Signature Algorithm) and ElGamal. The versatile interface
allows to add more algorithms in the future.
The API is based on data structures called S-expressions (see XXXX)
and does not work with contexts as most of the other building blocks
Libgcrypt provides.
@noindent
To describe how Libgcrypt expect keys, we use some examples. Note that
words in
@ifnottex
uppercase
@end ifnottex
@iftex
italics
@end iftex
indicate parameters whereas lowercase words are literals.
@example
(private-key
(dsa
(p @var{p-mpi})
(q @var{q-mpi})
(g @var{g-mpi})
(y @var{y-mpi})
(x @var{x-mpi})))
@end example
@noindent
This specifies an DSA private key with the following parameters:
@table @var
@item p-mpi
DSA prime @math{p}.
@item q-mpi
DSA group order @math{q} (which is a prime divisor of @math{p-1}).
@item g-mpi
DSA group generator @math{g}.
@item y-mpi
DSA public key value @math{y = g^x \bmod p}.
@item x-mpi
DSA secret exponent x.
@end table
All the MPI values are expected to be in @code{GCRYMPI_FMT_USG} format.
The public key is similar with "private-key" replaced by "public-key"
and no @var{x-mpi}.
An easy way to create such an S-expressions is by using
@code{gcry_sexp_build} which allows to pass a string with printf-like
escapes to insert MPI values.
@noindent
Here is an example for an RSA key:
@example
(private-key
(rsa
(n @var{n-mpi})
(e @var{e-mpi})
(d @var{d-mpi})
(p @var{p-mpi})
(q @var{q-mpi})
(u @var{u-mpi})
@end example
@noindent
with
@table @var
@item n-mpi
RSA public modulus @math{n}.
@item e-mpi
RSA public exponent @math{e}.
@item d-mpi
RSA secret exponent @math{d = e^{-1} \bmod (p-1)(q-1)}.
@item p-mpi
RSA secret prime @math{p}.
@item q-mpi
RSA secret prime @math{q} with @math{q > p}.
@item u-mpi
multiplicative inverse @math{u = p^{-1} \bmod q}.
@end table
@noindent
Note, that we will in future allow to use keys without p,q and u
specified and may also support other parameters for performance
reasons.
@noindent
Now that we know the key basics, we can carry on and explain how to
encrypt and decrypt data. In almost all cases the data is a random
session key which is in turn used for the actual encryption of the real
data. There are 2 functions to do this:
@deftypefun int gcry_pk_encrypt (@w{GcrySexp *@var{r_ciph},} @w{GcrySexp @var{data},} @w{GcrySexp @var{pkey}})
Obviously a public key must be provided for encryption. It is expected
as an appropriate S-expression (see above) in @var{pkey}. The data to
be encrypted can either be in the simple old format, which is a very
simple S-expression consisting only of one MPI, or it may be a more
complex S-expression which also allows to specify padding rules.
@noindent
If you don't want to let Libgcrypt handle the padding, you must pass an
appropriate MPI using the this expression for @var{data}:
@example
(data
(flags raw)
(value @var{mpi}))
@end example
@noindent
This has the same semantics as the old style MPI only way. @var{MPI} is
the actual data, already padded appropriate for your protocol. Most
systems however use PKCS#1 padding and so you can use this S-expression
for @var{data}:
@example
(data
(flags pkcs1)
(value @var{block}))
@end example
@noindent
Here, the "flags" list has the "pkcs1" flag which let the function know
that it should provide PKCS#1 block type 2 padding. The actual data to
be encrypted is passed as a string of octets in @var{block}. The
function checks that this data actually can be used with the given key,
does the padding and encrypts it.
If the function could successfully perform the encryption, the return
value will be 0 and a a new S-expression with the encrypted result is
allocated and assign to the variable at the address of @var{r_ciph}.
The caller is responsible to release this value using
@code{gcry_sexp_release}. In case of an error, an error code is
returned and @var{r_ciph} will be set to @code{NULL}.
@noindent
The returned S-expression has this format when used with RSA:
@example
(enc-val
(rsa
(a @var{a-mpi})))
@end example
@noindent
Where @var{a-mpi} is an MPI with the result of the RSA operation. When
using the ElGamal algorithm, the return value will have this format:
@example
(enc-val
(elg
(a @var{a-mpi})
(b @var{b-mpi})))
@end example
@noindent
Where @var{a-mpi} and @var{b-mpi} are MPIs with the result of the
ElGamal encryption operation.
@end deftypefun
@c end gcry_pk_encrypt
@deftypefun int gcry_pk_decrypt (@w{GcrySexp *@var{r_plain},} @w{GcrySexp @var{data},} @w{GcrySexp @var{skey}})
Obviously a private key must be provided for decryption. It is expected
as an appropriate S-expression (see above) in @var{skey}. The data to
be decrypted must match the format of the result as returned by
@code{gcry_pk_encrypt}. Note that this function does not know of any
padding and the caller must do any un-padding on his own.
@noindent
The function returns 0 on success or an error code. The variable at the
address of @var{r_plain} will be set to NULL on error or receive the
decrypted value on success. The format of @var{r_plain} is currently a
simple S-expression with just one MPI.
@end deftypefun
@c end gcry_pk_decrypt
Another operation commonly performed using public keys are digital
signature. In some sense they are even more important than the
encryption because digital signature are an important instrument for key
management. Libgcrypt support digital signatures using 2 functions,
similar to the encryption functions:
@deftypefun int gcry_pk_sign (@w{GcrySexp *@var{r_sig},} @w{GcrySexp @var{data},} @w{GcrySexp @var{skey}})
This function creates a digital signature for @var{data} using the
private key @var{skey} and place it into the variable at the address of
@var{r_sig}. @var{data} may either be the simple old style S-expression
with just one MPI or a modern and more versatile S-expression which
allows to let Libgcrypt handle padding:
@example
(data
(flags pkcs1)
(hash @var{hash-algo} @var{block}))
@end example
@noindent
This example requests to sign the data in @var{block} after applying
PKCS#1 block type 1 style padding. @var{hash-algo} is a string with the
hash algorithm to be encoded into the signature, this may be any hash
algorithm name as supported by Libgcrypt. Most likely, this will be
"sha1", "rmd160" or "md5". It is obvious that the length of @var{block}
must match the size of that message digests; the function checks that
this and other constraints are valid.
@noindent
If PKCS#1 padding is not required (because the caller does already
provide a padded value), either the old format or better the following
format should be used:
@example
(data
(flags raw)
(value @var{mpi}))
@end example
@noindent
Here, the data to be signed is directly given as an @var{MPI}.
@noindent
The signature is returned as a newly allocated S-expression in
@var{r_sig} using this format for RSA:
@example
(sig-val
(rsa
(s @var{s-mpi})))
@end example
Where @var{s-mpi} is the result of the RSA sign operation. For DSA the
S-expression returned is:
@example
(sig-val
(dsa
(r @var{r-mpi})
(s @var{s-mpi})))
@end example
Where @var{r-mpi} and @var{s-mpi} are the result of the DSA sign
operation. For ElGamal signing (which is slow, yields large numbers
and probably is not as secure as the other algorithms), the same format is
used with "elg" replacing "dsa".
@end deftypefun
@c end gcry_pk_sign
@noindent
The operation most commonly used is definitely the verification of a
signature. Libgcrypt provides this function:
@deftypefun int gcry_pk_verify (@w{GcrySexp @var{sig}}, @w{GcrySexp @var{data}}, @w{GcrySexp @var{pkey}})
This is used to check whether the signature @var{sig} matches the
@var{data}. The public key @var{pkey} must be provided to perform this
verification. This function is similar in its parameters to
@code{gcry_pk_sign} with the exceptions that the public key is used
instead of the private key and that no signature is created but a
signature, in a format as created by @code{gcry_pk_sign}, is passed to
the function in @var{sig}.
@noindent
The result is 0 for success (i.e. the data matches the signature), or an
error code where the most relevant code is @code{GCRYERR_BAD_SIGNATURE}
to indicate that the signature does not match the provided data.
@end deftypefun
@c end gcry_pk_verify
@noindent
A couple of utility functions are available to retrieve the length of
the key, map algorithm identifiers and perform sanity checks:
@deftypefun {const char *} gcry_pk_algo_name (int @var{algo})
Map the public key algorithm id @var{algo} to a string representation of
the algorithm name. For unknown algorithms this functions returns an
empty string.
@end deftypefun
@deftypefun int gcry_pk_map_name (const char *@var{name})
Map the algorithm @var{name} to a public key algorithm Id. Returns 0 if
the algorithm name is not known.
@end deftypefun
@deftypefun int gcry_pk_test_algo (int @var{algo})
Return 0 if the public key algorithm @var{algo} is available for use.
@end deftypefun
@deftypefun {unsigned int} gcry_pk_get_nbits (GcrySexp @var{key})
Return what is commonly referred as the key length for the given
public or private in @var{key}.
@end deftypefun
@deftypefun {unsigned char *} gcry_pk_get_keygrip (@w{GcrySexp @var{key}}, @w{unsigned char *@var{array}})
Return the so called "keygrip" which is the SHA-1 hash of the public key
parameters expressed in a way depended on the algorithm. @var{array}
must either provide space for 20 bytes or @code{NULL;}. In the latter
case a newly allocated array of that size is returned. On success a
pointer to the newly allocated space or to @var{array} is returned.
@code{NULL} is returned to indicate an error which is most likely an unknown
algorithm or one where a "keygrip" has not yet been defined.
The function accepts public or secret keys in @var{key}.
@end deftypefun
@deftypefun int gcry_pk_testkey (GcrySexp @var{key})
Return 0 if @var{key} (either private or public) is sane.
@end deftypefun
@deftypefun int gcry_pk_algo_info (@w{int @var{algo}}, @w{int @var{what}}, @w{void *@var{buffer}}, @w{size_t *@var{nbytes}})
Depending on the value of @var{what} return various information about
the public key algorithm with the id @var{algo}. Note, that the
function returns @code{-1} on error and the actual error code must be
retrieved using the function @code{gcry_errno}. The currently defined
values for @var{what} are:
@table @code
@item GCRYCTL_TEST_ALGO:
Return 0 when the specified algorithm is available for use.
@var{buffer} must be @code{NULL}, @var{nbytes} may be passed as
@code{NULL} or point to a variable with the required usage of the
algorithm. This may be 0 for "don't care" or the bit-wise OR of these
flags:
@table @code
@item GCRY_PK_USAGE_SIGN
Algorithm is usable for signing.
@item GCRY_PK_USAGE_ENCR
Algorithm is usable for encryption.
@end table
@item GCRYCTL_GET_ALGO_USAGE:
Return the usage flags for the given algorithm. An invalid algorithm
return 0. Disabled algorithms are ignored here because we
want to know whether the algorithm is at all capable of a certain usage.
@item GCRYCTL_GET_ALGO_NPKEY
Return the number of elements the public key for algorithm @var{algo}
consist of. Return 0 for an unknown algorithm.
@item GCRYCTL_GET_ALGO_NSKEY
Return the number of elements the private key for algorithm @var{algo}
consist of. Note that this value is always larger than that of the
public key. Return 0 for an unknown algorithm.
@item GCRYCTL_GET_ALGO_NSIGN
Return the number of elements a signature created with the algorithm
@var{algo} consists of. Return 0 for an unknown algorithm or for an
algorithm not capable of creating signatures.
@item GCRYCTL_GET_ALGO_NENC
Return the number of elements a encrypted message created with the algorithm
@var{algo} consists of. Return 0 for an unknown algorithm or for an
algorithm not capable of encryption.
@end table
@noindent
Please note that parameters not required should be passed as @code{NULL}.
@end deftypefun
@c end gcry_pk_algo_info
@deftypefun int gcry_pk_ctl (@w{int @var{cmd}}, @w{void *@var{buffer}}, @w{size_t @var{buflen}})
This is a general purpose function to perform certain control
operations. @var{cmd} controls what is to be done. The return value is
0 for success or an error code. Currently supported values for
@var{cmd} are:
@table @code
@item GCRYCTL_DISABLE_ALGO
Disable the algorithm given as an algorithm id in @var{buffer}.
@var{buffer} must point to an @code{int} variable with the algorithm id
and @var{buflen} must have the value @code{sizeof (int)}.
@end table
@end deftypefun
@c end gcry_pk_ctl
@noindent
Libgcrypt also provides a function to generate public key pairs:
@deftypefun int gcry_pk_genkey (@w{GcrySexp *@var{r_key}}, @w{GcrySexp @var{parms}})
This function create a new public key pair using information given in
the S-expression @var{parms} and stores the private and the public key
in one new S-expression at the address given by @var{r_key}. In case of
an error, @var{r_key} is set to @code{NULL}. The return code is 0 for
success or an error code otherwise.
@noindent
Here is an example for @var{parms} for creating a 1024 bit RSA key:
@example
(genkey
(rsa
(nbits 1024)))
@end example
@noindent
To create an ElGamal key, substitute "elg" for "rsa" and to create a DSA
key use "elg". Valid ranges for the key length depend on the
algorithms; all commonly used key lengths are supported.
@noindent
The key pair is returned in a format depending on the
algorithm. Both, private and secret, keys are returned and my be accompanied
by some miscellaneous information. The format resembles closely the one
of the public respectively the private key. Frankly, they are put into
one container, so that they can easily be extracted.
@noindent
As an example, here is what the ElGamal key generation returns:
@example
(key-data
(public-key
(elg
(p @var{p-mpi})
(g @var{g-mpi})
(y @var{y-mpi})))
(private-key
(elg
(p @var{p-mpi})
(g @var{g-mpi})
(y @var{y-mpi})
(x @var{x-mpi})))
(misc-key-info
(pm1-factors @var{n1 n2 ... nn})))
@end example
@noindent
As you can see, some of the information is duplicated, but this provides
an easy way to extract either the public or the private key. Note that
the order of the elements is not defined, e.g. the private key may be
stored before the public key. @var{n1 n2 ... nn} is a list of prime
numbers used to composite @var{p-mpi}; this is in general not a very
useful information.
@end deftypefun
@c end gcry_pk_genkey
@c **********************************************************
@c ******************* Random *****************************
@c **********************************************************
@node Random Numbers
@chapter Random Numbers
@deftypefun void gcry_randomize (unsigned char *@var{buffer}, size_t @var{length}, enum gcry_random_level @var{level})
Fill @var{buffer} with @var{length} random bytes using a random quality
as defined by @var{level}.
@end deftypefun
@deftypefun void * gcry_random_bytes (size_t @var{nbytes}, enum gcry_random_level @var{level})
Allocate a memory block consisting of @var{nbytes} fresh random bytes
using a random quality as defined by @var{level}.
@end deftypefun
@deftypefun void * gcry_random_bytes_secure (size_t @var{nbytes}, enum gcry_random_level @var{level})
Allocate a memory block consisting of @var{nbytes} fresh random bytes
using a random quality as defined by @var{level}. This function
differs from @code{gcry_random_bytes} in that the returned buffer is
allocated in a ``secure'' area of the memory.
@end deftypefun
@c **********************************************************
@c ******************* S-Expressions ***********************
@c **********************************************************
@node S-expressions
@chapter S-expressions
S-expressions are used by the public key functions to pass complex data
structures around. These LISP like objects are used by some
cryptographic protocols (cf. RFC-2692) and Libgcrypt provides functions
to parse and construct them. For detailed information, see
@cite{Ron Rivest, code and description of S-expressions,
@uref{http://theory.lcs.mit.edu/~rivest/sexp.html}}.
@deftp {Data type} GcrySexp
The @code{GcrySexp} type describes an object with the Libgcrypt internal
representation of an S-expression.
@end deftp
@noindent
There are several functions to create an Libgcrypt S-expression object
from its external representation or from a string template. There is
also a function to convert the internal representation back into one of
the external formats:
@deftypefun int gcry_sexp_new (@w{GcrySexp *@var{r_sexp}}, @w{const void *@var{buffer}}, @w{size_t @var{length}}, @w{int @var{autodetect}})
This is the generic function to create an new S-expression object from
its external representation in @var{buffer} of @var{length} bytes. On
success the result is stored at the address given by @var{r_sexp}.
With @var{autodetect} set to 0, the data in @var{buffer} is expected to
be in canonized format, with @var{autodetect} set to 1 the parses any of
the defined external formats. If @var{buffer} does not hold a valid
S-expression an error code is returned and @var{r_sexp} set to
@code{NULL}.
Note, that the caller is responsible for releasing the newly allocated
S-expression using @code{gcry_sexp_release}.
@end deftypefun
@deftypefun int gcry_sexp_create (@w{GcrySexp *@var{r_sexp}}, @w{void *@var{buffer}}, @w{size_t @var{length}}, @w{int @var{autodetect}}, @w{void (*@var{freefnc})(void*)})
This function is identical to @code{gcry_sexp_new} but has an extra
argument @var{freefnc}, which, when not set to @code{NULL}, is expected
to be a function to release the @var{buffer}; most likely the standard
@code{free} function is used for this argument. This has the effect of
transferring the ownership of @var{buffer} to the created object in
@var{r_sexp}. The advantage of using this function is that Libgcrypt
might decide to directly use the provided buffer and thus avoid extra
copying.
@end deftypefun
@deftypefun int gcry_sexp_sscan (@w{GcrySexp *@var{r_sexp}}, @w{size_t *@var{erroff}}, @w{const char *@var{buffer}}, @w{size_t @var{length}})
This is another variant of the above functions. It behaves nearly
identical but provides an @var{erroff} argument which will receive the
offset into the buffer where the parsing stopped on error.
@end deftypefun
@deftypefun int gcry_sexp_build (@w{GcrySexp *@var{r_sexp}}, @w{size_t *@var{erroff}}, @w{const char *@var{format}, ...})
This function creates an internal S-expression from the string template
@var{format} and stores it at the address of @var{r_sexp}. If there is a
parsing error, the function returns an appropriate error code and stores
the offset into @var{format} where the parsing stopped in @var{erroff}.
The function supports a couple of printf-like formatting characters and
expects arguments for some of these escape sequences right after
@var{format}. The following format characters are defined:
@table @samp
@item %m
The next argument is expected to be of type @code{GcryMPI} and a copy of
its value is inserted into the resulting S-expression.
@item %s
The next argument is expected to be of type @code{char *} and that
string is inserted into the resulting S-expression.
@item %d
The next argument is expected to be of type @code{int} and its
value ist inserted into the resulting S-expression.
@end table
@noindent
No other format characters are defined and would return an error. Note,
that the format character @samp{%%} does not exists, because a percent
sign is not a valid character in an S-expression.
@end deftypefun
@deftypefun void gcry_sexp_release (@w{GcrySexp @var{sexp}})
Release the S-expression object @var{sexp}.
@end deftypefun
@noindent
The next 2 functions are used to convert the internal representation
back into a regular external S-expression format and to show the
structure for debugging.
@deftypefun size_t gcry_sexp_sprint (@w{GcrySexp @var{sexp}}, @w{int @var{mode}}, @w{char *@var{buffer}}, @w{size_t @var{maxlength}})
Copies the S-expression object @var{sexp} into @var{buffer} using the
format specified in @var{mode}. @var{maxlength} must be set to the
allocated length of @var{buffer}. The function returns the actual
length of valid bytes put into @var{buffer} or 0 if the provided buffer
is too short. Passing @code{NULL} for @var{buffer} returns the required
length for @var{buffer}. For convenience reasons an extra byte with
value 0 is appended to the buffer.
@noindent
The following formats are supported:
@table @code
@item GCRYSEXP_FMT_DEFAULT
Returns a convenient external S-expression representation.
@item GCRYSEXP_FMT_CANON
Return the S-expression in canonical format.
@item GCRYSEXP_FMT_BASE64
Not currently supported.
@item GCRYSEXP_FMT_ADVANCED
Returns the S-expression in advanced format.
@end table
@end deftypefun
@deftypefun void gcry_sexp_dump (@w{GcrySexp @var{sexp}})
Dumps @var{sexp} in a format suitable for debugging to Libgcrypt's
logging stream.
@end deftypefun
@noindent
Often canonical encoding is used in the external representation. The
following function can be used to check for valid encoding and to learn
the length of the S-expression"
@deftypefun size_t gcry_sexp_canon_len (@w{const unsigned char *@var{buffer}}, @w{size_t @var{length}}, @w{size_t *@var{erroff}}, @w{int *@var{errcode}})
Scan the canonical encoded @var{buffer} with implicit length values and
return the actual length this S-expression uses. For a valid S-expression
it should never return 0. If @var{length} is not 0, the maximum
length to scan is given; this can be used for syntax checks of
data passed from outside. @var{errcode} and @var{erroff} may both be
passed as @code{NULL}.
@noindent
@strong{Warning:} For historical reasons the error codes returned in
@var{errcode} are negative numbers and don't match the regular error
codes. To convert to regular error codes, use the simple formula
@code{rc = 200 - errcode}.
@end deftypefun
@noindent
There are a couple of functions to parse S-expressions and retrieve
elements:
@deftypefun GcrySexp gcry_sexp_find_token (@w{const GcrySexp @var{list}}, @w{const char *@var{token}}, @w{size_t @var{toklen}})
Scan the S-expression for a sublist with a type (the car of the list)
matching the string @var{token}. If @var{toklen} is not 0, the token is
assumed to be raw memory of this length. The function returns a newly
allocated S-expression consisting of the found sublist or @code{NULL}
when not found.
@end deftypefun
@deftypefun int gcry_sexp_length (@w{const GcrySexp @var{list}})
Return the length of the @var{list}. For a valid S-expression this
should be at least 1.
@end deftypefun
@deftypefun GcrySexp gcry_sexp_nth (@w{const GcrySexp @var{list}}, @w{int @var{number}})
Create and return a new S-expression from the element with index @var{number} in
@var{list}. Note that the first element has the index 0. If there is
no such element, @code{NULL} is returned.
@end deftypefun
@deftypefun GcrySexp gcry_sexp_car (@w{const GcrySexp @var{list}})
Create and return a new S-expression from the first element in
@var{list}; this called the "type" and should always exist and be a
string. @code{NULL} is returned in case of a problem.
@end deftypefun
@deftypefun GcrySexp gcry_sexp_cdr (@w{const GcrySexp @var{list}})
Create and return a new list form all elements except for the first one.
Note, that this function may return an invalid S-expression because it
is not guaranteed, that the type exists and is a string. However, for
parsing a complex S-expression it might be useful for intermediate
lists. Returns @code{NULL} on error.
@end deftypefun
@deftypefun {const char *} gcry_sexp_nth_data (@w{const GcrySexp @var{list}}, @w{int @var{number}}, @w{size_t *@var{datalen}})
This function is used to get data from a @var{list}. A pointer to the
actual data with index @var{number} is returned and the length of this
data will be stored to @var{datalen}. If there is no data at the given
index or the index represents another list, @code{NULL} is returned.
@strong{Note:} The returned pointer is valid as long as @var{list} is
not modified or released.
@noindent
Here is an example on how to extract and print the surname (Meier) from
the S-expression @samp{(Name Otto Meier (address Burgplatz 3))}:
@example
size_t len;
const char *name;
name = gcry_sexp_nth_data (list, 2, &len);
printf ("my name is %.*s\n", (int)len, name);
@end example
@end deftypefun
@deftypefun GcryMPI gcry_sexp_nth_mpi (@w{GcrySexp @var{list}}, @w{int @var{number}}, @w{int @var{mpifmt}})
This function is used to get and convert data from a @var{list}. This
data is assumed to be an MPI stored in the format described by
@var{mpifmt} and returned as a standard Libgcrypt MPI. The caller must
release this returned value using @code{gcry_mpi_release}. If there is
no data at the given index, the index represents a list or the value
can't be converted to an MPI, @code{NULL} is returned.
@end deftypefun
@c **********************************************************
@c ******************* MPIs ******** ***********************
@c **********************************************************
@node MPI Functions
@chapter MPI Functions
Public key cryptography is based on mathematics with large numbers. To
implement the public key functions, a library for handling these large
numbers is required. Because of the general usefulness of such a
library, its interface is exposed by Libgcrypt. The implementation is
based on an old release of GNU Multi-Precision Library (GMP) but in the
meantime heavily modified and stripped down to what is required for
cryptography. For a lot of CPUs, high performance assembler
implementations of some very low level functions are used to gain much
better performance than with the standard C implementation.
@noindent
In the context of Libgcrypt and in most other applications, these large
numbers are called MPIs (multi-precision-integers).
@deftp {Data type} GcryMPI
The @code{GcryMPI} type represents an object to hold an MPI.
@end deftp
@noindent
To work with MPIs, storage must be allocated and released for the
numbers. This can be done with one of these functions:
@deftypefun GcryMPI gcry_mpi_new (@w{unsigned int @var{nbits}})
Allocate a new MPI object, initialize it to 0 and initially allocate
enough memory for a number of at least @var{nbits}. This pre-allocation is
only a small performance issue and not actually necessary because
Libgcrypt automatically re-allocates the required memory.
@end deftypefun
@deftypefun GcryMPI gcry_mpi_snew (@w{unsigned int @var{nbits}})
This is identical to @code{gcry_mpi_new} but allocates the MPI in the so
called "secure memory" which in turn will take care that all derived
values will also be stored in this "secure memory". Use this for highly
confidential data like private key parameters.
@end deftypefun
@deftypefun GcryMPI gcry_mpi_copy (@w{const GcryMPI @var{a}})
Create a new MPI as the exact copy of @var{a}.
@end deftypefun
@deftypefun void gcry_mpi_release (@w{GcryMPI @var{a}})
Release the MPI @var{a} and free all associated resources. Passing
@code{NULL} is allowed and ignored. When a MPI stored in the "secure
memory" is released, that memory gets wiped out immediately.
@end deftypefun
@noindent
The simplest operations are used to assign a new value to an MPI:
@deftypefun GcryMPI gcry_mpi_set (@w{GcryMPI @var{w}}, @w{const GcryMPI @var{u}})
Assign the value of @var{u} to @var{w} and return @var{w}. If
@code{NULL} is passed for @var{w}, a new MPI is allocated, set to the
value of @var{u} and returned.
@end deftypefun
@deftypefun GcryMPI gcry_mpi_set_ui (@w{GcryMPI @var{w}}, @w{unsigned long @var{u}})
Assign the value of @var{u} to @var{w} and return @var{w}. If
@code{NULL} is passed for @var{w}, a new MPI is allocated, set to the
value of @var{u} and returned. This function takes an @code{unsigned
int} as type for @var{u} and thus it is only possible to set @var{w} to
small values (usually up to the word size of the CPU).
@end deftypefun
@deftypefun void gcry_mpi_swap (@w{GcryMPI @var{a}}, @w{GcryMPI @var{b}})
Swap the values of @var{a} and @var{b}.
@end deftypefun
@noindent
The following functions are used to convert between an external
representation of an MPI and the internal one of Libgcrypt.
@deftypefun int gcry_mpi_scan (@w{GcryMPI *@var{r_mpi}}, @w{enum gcry_mpi_format @var{format}}, @w{const char *@var{buffer}}, @w{size_t *@var{nbytes}})
Convert the external representation of an integer stored in @var{buffer}
with a length stored at the address of @var{nbytes} into a newly created
MPI returned which will be stored at the address of @var{r_mpi}. For
certain formats the length argument is not required and may be passed as
@code{NULL}. After a successful operation the variable @var{nbytes}
points to, receives the number of bytes actually scanned. @var{format}
describes the format of the MPI as stored in @var{buffer}:
@table @code
@item GCRYMPI_FMT_STD
2-complement stored without a length header.
@item GCRYMPI_FMT_PGP
As used by OpenPGP (only defined as unsigned). This is basically
@code{GCRYMPI_FMT_STD} with a 2 byte big endian length header.
@item GCRYMPI_FMT_SSH
As used in the Secure Shell protocol. This is @code{GCRYMPI_FMT_STD}
with a 4 byte big endian header.
@item GCRYMPI_FMT_HEX
Stored as a C style string with each byte of the MPI encoded as 2 hex
digits.
@item GCRYMPI_FMT_USG
Simple unsigned integer.
@end table
@noindent
Note, that all of the above formats store the integer in big-endian
format (MSB first).
@end deftypefun
@deftypefun int gcry_mpi_print (@w{enum gcry_mpi_format @var{format}}, @w{char *@var{buffer}}, @w{size_t *@var{nbytes}}, @w{const GcryMPI @var{a}})
Convert the MPI @var{a} into an external representation described by
@var{format} (see above) and store it in the provided @var{buffer} which
which has a usable length of at least the number of bytes stored in the
variable @var{nbytes} points to; this variable will receive the actual
number of bytes stored after a successful operation.
@end deftypefun
@deftypefun int gcry_mpi_aprint (@w{enum gcry_mpi_format @var{format}}, @w{void **@var{buffer}}, @w{size_t *@var{nbytes}}, @w{const GcryMPI @var{a}})
Convert the MPI @var{a} into an external representation described by
@var{format} (see above) and store it in a newly allocated buffer which
address will be stored in the variable @var{buffer} points to. The
number of bytes stored in this buffer will be stored in the variable
@var{nbytes} points to, unless @var{nbytes} is @code{NULL}.
@end deftypefun
@noindent
Basic arithmetic operations:
@deftypefun void gcry_mpi_add (@w{GcryMPI @var{w}}, @w{GcryMPI @var{u}}, @w{GcryMPI @var{v}})
@math{@var{w} = @var{u} + @var{v}}.
@end deftypefun
@deftypefun void gcry_mpi_add_ui (@w{GcryMPI @var{w}}, @w{GcryMPI @var{u}}, @w{unsigned long @var{v}})
@math{@var{w} = @var{u} + @var{v}}. Note, that @var{v} is an unsigned integer.
@end deftypefun
@deftypefun void gcry_mpi_addm (@w{GcryMPI @var{w}}, @w{GcryMPI @var{u}}, @w{GcryMPI @var{v}}, @w{GcryMPI @var{m}})
@math{var{w} = @var{u} + @var{v} \bmod @var{m}}.
@end deftypefun
@deftypefun void gcry_mpi_sub (@w{GcryMPI @var{w}}, @w{GcryMPI @var{u}}, @w{GcryMPI @var{v}})
@math{@var{w} = @var{u} - @var{v}}.
@end deftypefun
@deftypefun void gcry_mpi_sub_ui (@w{GcryMPI @var{w}}, @w{GcryMPI @var{u}}, @w{unsigned long @var{v}})
@math{@var{w} = @var{u} - @var{v}}. @var{v} is an unsigned integer.
@end deftypefun
@deftypefun void gcry_mpi_subm (@w{GcryMPI @var{w}}, @w{GcryMPI @var{u}}, @w{GcryMPI @var{v}}, @w{GcryMPI @var{m}})
@math{@var{w} = @var{u} - @var{v} \bmod @var{m}}.
@end deftypefun
@deftypefun void gcry_mpi_mul (@w{GcryMPI @var{w}}, @w{GcryMPI @var{u}}, @w{GcryMPI @var{v}})
@math{@var{w} = @var{u} * @var{v}}.
@end deftypefun
@deftypefun void gcry_mpi_mul_ui (@w{GcryMPI @var{w}}, @w{GcryMPI @var{u}}, @w{unsigned long @var{v}})
@math{@var{w} = @var{u} * @var{v}}. @var{v} is an unsigned integer.
@end deftypefun
@deftypefun void gcry_mpi_mulm (@w{GcryMPI @var{w}}, @w{GcryMPI @var{u}}, @w{GcryMPI @var{v}}, @w{GcryMPI @var{m}})
@math{@var{w} = @var{u} * @var{v} \bmod @var{m}}.
@end deftypefun
@deftypefun void gcry_mpi_mul_2exp (@w{GcryMPI @var{w}}, @w{GcryMPI @var{u}}, @w{unsigned long @var{e}})
@c FIXME: I am in need for a real TeX{info} guru:
@c I don't know why TeX can grok @var{e} here.
@math{@var{w} = @var{u} * 2^e}.
@end deftypefun
@deftypefun void gcry_mpi_div (@w{GcryMPI @var{q}}, @w{GcryMPI @var{r}}, @w{GcryMPI @var{dividend}}, @w{GcryMPI @var{divisor}}, @w{int @var{round}})
@math{@var{q} = @var{dividend} / @var{divisor}}, @math{@var{r} =
@var{dividend} \bmod @var{divisor}}. @var{q} and @var{r} may be passed
as @code{NULL}. @var{round} should be negative or 0.
@end deftypefun
@deftypefun void gcry_mpi_mod (@w{GcryMPI @var{r}}, @w{GcryMPI @var{dividend}}, @w{GcryMPI @var{divisor}})
@math{@var{r} = @var{dividend} \bmod @var{divisor}}.
@end deftypefun
@deftypefun void gcry_mpi_powm (@w{GcryMPI @var{w}}, @w{const GcryMPI @var{b}}, @w{const GcryMPI @var{e}}, @w{const GcryMPI @var{m}})
@c I don't know why TeX can grok @var{e} here.
@math{@var{w} = @var{b}^e \bmod @var{m}}.
@end deftypefun
@deftypefun int gcry_mpi_gcd (@w{GcryMPI @var{g}}, @w{GcryMPI @var{a}}, @w{GcryMPI @var{b}})
Set @var{g} to the greatest common divisor of @var{a} and @var{b}.
Return true if the @var{g} is 1.
@end deftypefun
@deftypefun int gcry_mpi_invm (@w{GcryMPI @var{x}}, @w{GcryMPI @var{a}}, @w{GcryMPI @var{m}})
Set @var{x} to the multiplicative inverse of @math{@var{a} \bmod @var{m}}.
Return true if the inverse exists.
@end deftypefun
@noindent
The next 2 functions are used to compare MPIs:
@deftypefun int gcry_mpi_cmp (@w{const GcryMPI @var{u}}, @w{const GcryMPI @var{v}})
Compare the big integer number @var{u} and @var{v} returning 0 for
equality, a positive value for @var{u} > @var{v} and a negative for
@var{u} < @var{v}.
@end deftypefun
@deftypefun int gcry_mpi_cmp_ui (@w{const GcryMPI @var{u}}, @w{unsigned long @var{v}})
Compare the big integer number @var{u} with the unsigned integer @var{v}
returning 0 for equality, a positive value for @var{u} > @var{v} and a
negative for @var{u} < @var{v}.
@end deftypefun
@noindent
There are a couple of functions to get information on arbitrary bits
in an MPI and to set or clear them:
@deftypefun {unsigned int} gcry_mpi_get_nbits (@w{GcryMPI @var{a}})
Return the number of bits required to represent @var{a}.
@end deftypefun
@deftypefun int gcry_mpi_test_bit (@w{GcryMPI @var{a}}, @w{unsigned int @var{n}})
Return true if bit number @var{n} (counting from 0) is set in @var{a}.
@end deftypefun
@deftypefun void gcry_mpi_set_bit (@w{GcryMPI @var{a}}, @w{unsigned int @var{n}})
Set bit number @var{n} in @var{a}.
@end deftypefun
@deftypefun void gcry_mpi_clear_bit (@w{GcryMPI @var{a}}, @w{unsigned int @var{n}})
Clear bit number @var{n} in @var{a}.
@end deftypefun
@deftypefun void gcry_mpi_set_highbit (@w{GcryMPI @var{a}}, @w{unsigned int @var{n}})
Set bit number @var{n} in @var{a} and clear all bits greater than @var{n}.
@end deftypefun
@deftypefun void gcry_mpi_clear_highbit (@w{GcryMPI @var{a}}, @w{unsigned int @var{n}})
Clear bit number @var{n} in @var{a} and all bits greater than @var{n}.
@end deftypefun
@deftypefun void gcry_mpi_rshift (@w{GcryMPI @var{x}}, @w{GcryMPI @var{a}}, @w{unsigned int @var{n}})
Shift the value of @var{a} by @var{n} bits to the right and store the
result in @var{x}.
@end deftypefun
@noindent
The remaining MPI functions take care of very special properties of the
implementation:
@deftypefun GcryMPI gcry_mpi_set_opaque (@w{GcryMPI @var{a}}, @w{void *@var{p}}, @w{unsigned int @var{nbits}})
Store @var{nbits} of the value @var{p} points to in @var{a} and mark
@var{a} as an opaque value (i.e. an value that can't be used for any
math calculation and is only used to store an arbitrary bit pattern in
@var{a}.
@end deftypefun
@deftypefun {void *} gcry_mpi_get_opaque (@w{GcryMPI @var{a}}, @w{unsigned int *@var{nbits}})
Return a pointer to an opaque value stored in @var{a} and return its
size in @var{nbits}. Note, that the returned pointer is still owned by
@var{a} and that the function should never be used for an non-opaque
MPI.
@end deftypefun
@deftypefun void gcry_mpi_set_flag (@w{GcryMPI @var{a}}, @w{enum gcry_mpi_flag @var{flag}})
Set the @var{flag} for the MPI @var{a}. Currently only the flag
@code{GCRYMPI_FLAG_SECURE} is allowed to convert @var{a} into an MPI
stored in "secure memory".
@end deftypefun
@deftypefun void gcry_mpi_clear_flag (@w{GcryMPI @var{a}}, @w{enum gcry_mpi_flag @var{flag}})
Clear @var{flag} for the big integer @var{a}. Note, that this function is
currently useless as no flags are allowed.
@end deftypefun
@deftypefun int gcry_mpi_get_flag (@w{GcryMPI @var{a}}, @w{enum gcry_mpi_flag @var{flag}})
Return true when the @var{flag} is set for @var{a}.
@end deftypefun
@c **********************************************************
@c ******************* Utilities **************************
@c **********************************************************
@node Utilities
@chapter Utilities
Helper functions.
@c <funcprototype>
@c <funcdef>int <function>gcry_control</function></funcdef>
@c <paramdef>enum gcry_ctl_cmds<parameter>cmd</parameter></paramdef>
@c <paramdef><parameter>...</parameter></paramdef>
@c </funcprototype>
@c </funcsynopsis>
@c </refsynopsisdiv>
@c
@c <refsect1><title>Description</title>
@c <para>
@c <indexterm><primary>gcry_control</primary></indexterm>
@c This function is used to control various aspects of &libgcrypt;
@c FIXME: Explain all commands here.
@c </para>
@c </refentry>
@c
@c
@c
@c
@c
@c <refentry>
@c <refnamediv>
@c <refname>gcry_set_allocation_handler</refname>
@c <refname>gcry_set_outofcore_handler</refname>
@c <refpurpose>Use application defined malloc functions</refpurpose>
@c </refnamediv>
@c
@c <refsynopsisdiv>
@c <funcsynopsis>
@c <funcsynopsisinfo>
@c #include <gcrypt.h>
@c </funcsynopsisinfo>
@c <funcprototype>
@c <funcdef>void <function>gcry_set_allocation_handler</></funcdef>
@c <paramdef>void *(*<parameter>alloc_func</>)(size_t n)</paramdef>
@c <paramdef>void *(*<parameter>alloc_secure_func</>)(size_t n)</paramdef>
@c <paramdef>int (*<parameter>is_secure_func</>)(const void *p)</paramdef>
@c <paramdef>void *(*<parameter>realloc_func</>)(void *p, size_t n)</paramdef>
@c <paramdef>void (*<parameter>free_func</>)(void *p)</paramdef>
@c </funcprototype>
@c <funcprototype>
@c <funcdef>void <function>gcry_set_outofcore_handler</></funcdef>
@c
@c <paramdef>int (*<parameter>h</>)( void*, size_t, unsigned int ),
@c void *opaque )</paramdef>
@c </funcprototype>
@c </funcsynopsis>
@c </refsynopsisdiv>
@c
@c <refsect1><title>Description</title>
@c <para>
@c <indexterm><primary>gcry_set_allocation_handler</primary></indexterm>
@c <indexterm><primary>gcry_set_outofcore_handler</primary></indexterm>
@c
@c FIXME
@c </para>
@c </refentry>
@c
@c
@c <refentry>
@c <refnamediv>
@c <refname>gcry_set_fatalerror_handler</refname>
@c <refpurpose>change the default fatal error handler</refpurpose>
@c </refnamediv>
@c
@c <refsynopsisdiv>
@c <funcsynopsis>
@c <funcsynopsisinfo>
@c #include <gcrypt.h>
@c </funcsynopsisinfo>
@c <funcprototype>
@c <funcdef>void <function>gcry_set_fatalerror_handler</></funcdef>
@c <paramdef>void (*<parameter>func</>)(
@c void *, int, const char*)</paramdef>
@c <paramdef>void *<parameter>opaque</></paramdef>
@c </funcprototype>
@c </funcsynopsis>
@c </refsynopsisdiv>
@c
@c <refsect1><title>Description</title>
@c <para>
@c <indexterm><primary>gcry_set_fatalerror_handler</primary></indexterm>
@c At certain places the &libgcrypt; may need to call a fatal error function
@c which does terminate the process. To allow an application to do
@c some emergency cleanup, it may register a fatal error handler with
@c the library. This handler is assumed to terminate the application;
@c however if it returns &libgcrypt; will abort anyway.
@c </para>
@c <para>
@c The handler is called with the opaque value registered here, an
@c errorcode from &libgcrypt; and some descriptive text string.
@c </para>
@c </refentry>
@c
@c
@c <refentry>
@c <refnamediv>
@c <refname>gcry_set_gettext_handler</refname>
@c <refpurpose>Change the default gettext function</refpurpose>
@c </refnamediv>
@c
@c <refsynopsisdiv>
@c <funcsynopsis>
@c <funcsynopsisinfo>
@c #include <gcrypt.h>
@c </funcsynopsisinfo>
@c <funcprototype>
@c <funcdef>void <function>gcry_set_gettext_handler</></funcdef>
@c <paramdef>const char *(*<parameter>func</>)(const char*)</paramdef>
@c <paramdef>void *<parameter>opaque</></paramdef>
@c </funcprototype>
@c </funcsynopsis>
@c </refsynopsisdiv>
@c
@c <refsect1><title>Description</title>
@c <para>
@c <indexterm><primary>gcry_set_log_handler</primary></indexterm>
@c FIXME!!
@c </para>
@c </refentry>
@c
@c
@c
@c <!--
@c void gcry_set_log_handler( void (*f)(void*,int, const char*, va_list ),
@c void
@c *opaque
@c );
@c -->
@c
@c <refentry>
@c <refnamediv>
@c <refname>gcry_set_log_handler</refname>
@c <refpurpose>Change the default logging function</refpurpose>
@c </refnamediv>
@c
@c <refsynopsisdiv>
@c <funcsynopsis>
@c <funcsynopsisinfo>
@c #include <gcrypt.h>
@c </funcsynopsisinfo>
@c <funcprototype>
@c <funcdef>void <function>gcry_set_log_handler</></funcdef>
@c <paramdef>void (*<parameter>func</>)
@c (void*, int, const char*, va_list)</paramdef>
@c <paramdef>void *<parameter>opaque</></paramdef>
@c </funcprototype>
@c </funcsynopsis>
@c </refsynopsisdiv>
@c
@c <refsect1><title>Description</title>
@c <para>
@c <indexterm><primary>gcry_set_log_handler</primary></indexterm>
@c &libgcrypt; has it;s own logging functions. Applications which
@c need to use their own, should provide a log function to &libgcrypt;
@c so that it will use this function instead.
@c
@c Fixme: Describe how this is intended to work.
@c </para>
@c </refentry>
@c
@c <!--
@c void *gcry_malloc( size_t n );
@c void *gcry_calloc( size_t n, size_t m );
@c void *gcry_malloc_secure( size_t n );
@c void *gcry_calloc_secure( size_t n, size_t m );
@c void *gcry_realloc( void *a, size_t n );
@c void *gcry_xmalloc( size_t n );
@c void *gcry_xcalloc( size_t n, size_t m );
@c void *gcry_xmalloc_secure( size_t n );
@c void *gcry_xcalloc_secure( size_t n, size_t m );
@c void *gcry_xrealloc( void *a, size_t n );
@c char *gcry_xstrdup( const char * a);
@c void gcry_free( void *a );
@c int gcry_is_secure( const void *a );
@c -->
@c
@c <refentry>
@c <refnamediv>
@c <refname>gcry_malloc</refname>
@c <refname>gcry_calloc</refname>
@c <refname>gcry_malloc_secure</refname>
@c <refname>gcry_calloc_secure</refname>
@c <refname>gcry_realloc</refname>
@c <refname>gcry_xmalloc</refname>
@c <refname>gcry_xcalloc</refname>
@c <refname>gcry_xmalloc_secure</refname>
@c <refname>gcry_xcalloc_secure</refname>
@c <refname>gcry_xrealloc</refname>
@c <refname>gcry_xstrdup</refname>
@c
@c <!-- WORk WORK -->
@c <refname>gcry_malloc</refname>
@c <refname>gcry_malloc</refname>
@c
@c <refpurpose>Change the default logging function</refpurpose>
@c </refnamediv>
@c
@c <refsynopsisdiv>
@c <funcsynopsis>
@c <funcsynopsisinfo>
@c #include <gcrypt.h>
@c </funcsynopsisinfo>
@c <funcprototype>
@c <funcdef>void <function>gcry_set_log_handler</></funcdef>
@c <paramdef>void (*<parameter>func</>)
@c (void*, int, const char*, va_list)</paramdef>
@c <paramdef>void *<parameter>opaque</></paramdef>
@c </funcprototype>
@c </funcsynopsis>
@c </refsynopsisdiv>
@c
@c <refsect1><title>Description</title>
@c <para>
@c <indexterm><primary>gcry_set_log_handler</primary></indexterm>
@c &libgcrypt; has it;s own logging functions. Applications which
@c need to use their own, should provide a log function to &libgcrypt;
@c so that it will use this function instead.
@c
@c Fixme: Describe how this is intended to work.
@c </para>
@c </refentry>
@c
@c
@c **********************************************************
@c ******************* Errors ****************************
@c **********************************************************
@node Error Handling
@chapter Error Handling
Most functions in Libgcrypt are returning 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 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.
@menu
* Error values:: A list of all error values used.
* Error strings:: How to get a descriptive string from a value.
@end menu
@node Error values
@section Error values
Errors are return as an @code{int}
Except for the EOF and No_Error cases an application should always
use the constants. Possible values are:
@table @code
@item GCRYERR_EOF
This value indicates the end of a list, buffer or file and is defined to have
the value @code{-1}.
@item GCRYERR_SUCCESS
This value indicates success. The value of this error code is
guaranteed to be @code{0}.
@item GCRYERR_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 GCRYERR_INV_PK_ALGO
Invalid public key algorithm.
@item GCRYERR_INV_MD_ALGO
Invalid message digest algorithm.
@item GCRYERR_BAD_PUBLIC_KEY
Bad public key.
@item GCRYERR_BAD_SECRET_KEY
Bad secret key.
@item GCRYERR_BAD_SIGNATURE
Bad signature.
@item GCRYERR_INV_CIPHER_ALGO
Invalid cipher algorithm.
@item GCRYERR_BAD_MPI
Problem with an MPI's value.
@item GCRYERR_WRONG_PK_ALGO
Wrong public key algorithm.
@item GCRYERR_WEAK_KEY
Weak encryption key detected.
@item GCRYERR_INV_KEYLEN
Invalid length of a key.
@item GCRYERR_INV_ARG
Invalid argument.
@item GCRYERR_SELFTEST
A self test failed.
@item GCRYERR_INV_OP
Invalid operation code or control command.
@item GCRYERR_NO_MEM
Out of core; not enough memory available to perform operation.
@item GCRYERR_INTERNAL
Internal error. This is most likely a bug in Libgcrypt or due to an
incomplete build or installation.
@item GCRYERR_EOF = 64
End-of-file condition. Note, that some functions usually return
@code{-1} to indicate this; Libgcrypt error function maps this to this
value.
@item GCRYERR_INV_OBJ
An object is not valid.
@item GCRYERR_TOO_SHORT
Provided buffer or object too short.
@item GCRYERR_TOO_LARGE
Object is too large.
@item GCRYERR_NO_OBJ
Missing item in an object.
@item GCRYERR_NOT_IMPL
Not implemented.
@item GCRYERR_CONFLICT
Conflicting use of function or values.
@item GCRYERR_INV_CIPHER_MODE
Invalid or unsupported cipher mode.
@item GCRYERR_INV_FLAG
Invalid flag.
@item GCRYERR_SEXP_INV_LEN_SPEC
The S-expression has an invalid length specification.
@item GCRYERR_SEXP_STRING_TOO_LONG
The encoded length of an S-expression is longer than the entire object.
@item GCRYERR_SEXP_UNMATCHED_PAREN
There are unmatched parenthesis in the S-expression.
@item GCRYERR_SEXP_NOT_CANONICAL
Not a canonical encoded S-expression.
@item GCRYERR_SEXP_BAD_CHARACTER
Bad character detected in an S-expression.
@item GCRYERR_SEXP_BAD_QUOTATION
Bad quotation in an S-expression. Might also indicate an invalid hex or
octal value.
@item GCRYERR_SEXP_ZERO_PREFIX
The length field of an S-expression element is prefixed with a 0.
@item GCRYERR_SEXP_NESTED_DH
Nested display hints found in an S-expression.
@item GCRYERR_SEXP_UNMATCHED_DH
Unmatched display hint found in an S-expression.
@item GCRYERR_SEXP_UNEXPECTED_PUNC
Unexpected reserved punctuation found in an S-expression.
@item GCRYERR_SEXP_BAD_HEX_CHAR
A bad hexadecimal character was found in an S-expression
@item GCRYERR_SEXP_ODD_HEX_NUMBERS
An odd number of hexadecimal characters was found in an S-expression.
@item GCRYERR_SEXP_BAD_OCT_CHAR
A bad octal character was found in an S-expression.
@end table
@node Error strings
@section Error strings
@deftypefun {const char *} gcry_strerror (@w{int @var{err}})
The function @code{gcry_strerror} returns a pointer to a statically
allocated string containing a description of the error with the error
value @var{err}. This string can be used to output a diagnostic
message to the user.
@end deftypefun
@c **********************************************************
@c ******************* Appendices *************************
@c **********************************************************
@include lgpl.texi
@include gpl.texi
@include fdl.texi
@node Concept Index
@unnumbered Concept Index
@printindex cp
@node Function and Data Index
@unnumbered Function and Data Index
@printindex fn
@summarycontents
@contents
@bye
@c LocalWords: int HD
distrib
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Mandriva
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i586
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media
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by-pkgid
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e51cc9a7ceca4751c9460cf73e4362b4
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