This is gcrypt.info, produced by makeinfo version 4.2 from gcrypt.texi. INFO-DIR-SECTION GNU Libraries START-INFO-DIR-ENTRY * libgcrypt: (gcrypt) Cryptographic function library. END-INFO-DIR-ENTRY This file documents the `Libgcrypt' library. This is Edition 1.1.10, last updated 14 August 2002, of `The `Libgcrypt' Reference Manual', for Version 1.1.10. Copyright (C) 2000, 2002 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". File: gcrypt.info, Node: Top, Next: Introduction, Up: (dir) Main Menu ********* This is Edition 1.1.10, last updated 14 August 2002, of `The `Libgcrypt' Reference Manual', for Version 1.1.10 of the GPGME library. * 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. * 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. File: gcrypt.info, Node: Introduction, Next: Preparation, Prev: Top, Up: Top Introduction ************ `Libgcrypt' is a library to provide cryptographic building blocks. * Menu: * Getting Started:: * Features:: * Overview:: File: gcrypt.info, Node: Getting Started, Next: Features, Up: Introduction 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. File: gcrypt.info, Node: Features, Next: Overview, Prev: Getting Started, Up: Introduction Features ======== `Libgcrypt' might have a couple of advantages over other libraries doing a similar job. It's Free Software Anybody can use, modify, and redistribute it under the terms of the GNU Lesser General Public License (*note Library Copying::). Note, that some parts (which are not needed on a GNU or GNU/Linux system) are subject to the terms of the GNU General Public License (*note Copying::); please see the README file of the distribution for of list of these parts. It encapsulates the low level cryptography `Libgcrypt' a high level interface to cryptographic building blocks using an extendable and flexible API. File: gcrypt.info, Node: Overview, Prev: Features, Up: Introduction Overview ======== Blurb The `Libgcrypt' library is thread-safe. Well, we hope so ;-) File: gcrypt.info, Node: Preparation, Next: Cipher Functions, Prev: Introduction, Up: Top 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:: File: gcrypt.info, Node: Header, Next: Version Check, Up: Preparation 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: #include <gcrypt.h> The name space of `Libgcrypt' is `gcry_*' for function names, `Gcry*' for data types and `GCRY_*' for other symbols. In addition the same name prefixes with one prepended underscore are reserved for internal use and should never be used by an application. File: gcrypt.info, Node: Version Check, Next: Building the source, Prev: Header, Up: Preparation 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. - Function: const char *gcry_check_version (const char *REQ_VERSION) Check that the the version of the library is at minimum the one given as a string in REQ_VERSION and return the actual version string of the library; return NULL if the condition is not met. If `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 intializes some subsystems. In a multithreaded environment if should be called before any more threads are created. File: gcrypt.info, Node: Building the source, Prev: Version Check, Up: Preparation 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 `-I' option). However, the path to the include file is determined at the time the source is configured. To solve this problem, `Libgrypt' ships with a small helper program `libgcrypt-config' that knows the path to the include file and other configuration options. The options that need to be added to the compiler invocation at compile time are output by the `--cflags' option to `libgcrypt-config'. The following example shows how it can be used at the command line: gcc -c foo.c `libgcrypt-config --cflags` Adding the output of `libgcrypt-config --cflags' to the compilers command line will ensure that the compiler can find the `Libgcrypt' header file. A similar problem occurs when linking the program with the library. Again, the compiler has to find the library files. For this to work, the path to the library files has to be added to the library search path (via the `-L' option). For this, the option `--libs' to `libgcrypt-config' can be used. For convenience, this option also outputs all other options that are required to link the program with the `Libgcrypt' libararies (in particular, the `-lgcrypt' option). The example shows how to link `foo.o' with the `Libgcrypt' library to a program `foo'. gcc -o foo foo.o `libgcrypt-config --libs` Of course you can also combine both examples to a single command by specifying both options to `libgcrypt-config': gcc -o foo foo.c `libgcrypt-config --cflags --libs` File: gcrypt.info, Node: Cipher Functions, Next: Hash Functions, Prev: Preparation, Up: Top Cipher Functions **************** - Function: GCRY_CIPHER_HD gcry_cipher_open (int ALGO, int MODE, unsigned int FLAGS) This function creates the context required for most of the othercipher functions. In case of an error `NULL' is returned. - Function: void gcry_cipher_close (GCRY_CIPHER_HD H) This function releases the context created by `gcry_cipher_open'. - Function: int gcry_cipher_ctl (GCRY_CIPHER_HD H, int CMD, void *BUFFER, size_t BUFLEN) `gcry_cipher_ctl' controls various aspects of the cipher module and specific cipher contexts. Usually some more specialzed functions are used for this purpose. - Function: int gcry_cipher_setkey (GCRY_CIPHER_HD H, void *K, size_t L) Set the key used for encryption or decryption. Note, that this is implemented as a macro. - Function: int gcry_cipher_setiv (GCRY_CIPHER_HD H, void *K, size_t L) Set the initialization vector used for encryption or decryption. Note, that this is implemented as a macro. - Function: int gcry_cipher_sync (GCRY_CIPHER_HD H) Peform the a "sync" operation which is only used with certain modes. - Function: int gcry_cipher_info (GCRY_CIPHER_HD H, int WHAT, void *BUFFER, size_t *NBYTES) `gcry_cipher_info' is used to retrieve various information about a cipher context or the cipher module in general. Currently no information is available. - Function: int gcry_cipher_algo_info (int ALGO, int WHAT, void *BUFFER, size_t *NBYTES) fixme - Function: const char *gcry_cipher_algo_name (int ALGO) `gcry_cipher_algo_name' returns a string with the name of the cipher algorithm ALGO. If the algorithm s not known or an other error occured, an empty string is return. This function will never return `NULL'. - Function: int gcry_cipher_map_name (const char *NAME) `gcry_cipher_map_name' returns the algorithm identifier for the cipher algorithm described by the string NAME. If this algorithm is not available `0' is returned. - Function: int gcry_cipher_mode_from_oid (const char *STRING) Return the cipher mode associated with an ASN.1 object identifier. The object identifier is expected to be in the IETF-style dotted decimal notation. The function returns `0' for an unknown object identifier or when no mode is associated with it. - Function: int gcry_cipher_encrypt (GCRY_CIPHER_HD H, unsigned char *out, size_t OUTSIZE, const unsigned char *IN, size_t INLEN) `gcry_cipher_encrypt' is used to encrypt the data. This function can either work in place or with two buffers. Overlapping buffers are not allowed. - Function: int gcry_cipher_decrypt (GCRY_CIPHER_HD H, unsigned char *out, size_t OUTSIZE, const unsigned char *IN, size_t INLEN) `gcry_cipher_encrypt' is used to decrypt the data. This function can either work in place or with two buffers. Overlapping buffers are not allowed. File: gcrypt.info, Node: Hash Functions, Next: Public Key Functions, Prev: Cipher Functions, Up: Top Hash Functions ************** How to use cryptographic hash functions. File: gcrypt.info, Node: Public Key Functions, Next: Random Numbers, Prev: Hash Functions, Up: Top Public Key Functions ******************** How to use asymmetric encryption. File: gcrypt.info, Node: Random Numbers, Next: Utilities, Prev: Public Key Functions, Up: Top Random Numbers ************** - Function: void gcry_randomize (unsigned char *BUFFER, size_t LENGTH, enum gcry_random_level LEVEL) Fill BUFFER with LENGTH random bytes using a random quality as defined by LEVEL. - Function: void *gcry_random_bytes (size_t NBYTES, enum gcry_random_level LEVEL) Allocate a memory block consisting of NBYTES fresh random bytes using a random quality as defined by LEVEL. - Function: void *gcry_random_bytes_secure (size_t NBYTES, enum gcry_random_level LEVEL) Allocate a memory block consisting of NBYTES fresh random bytes using a random quality as defined by LEVEL. This fuinction differs from `gcry_random_bytes' in that the returned buffer is allcated in a "secure" area of the memory. File: gcrypt.info, Node: Utilities, Next: Error Handling, Prev: Random Numbers, Up: Top Utilities ********* Helper functions. File: gcrypt.info, Node: Error Handling, Next: Library Copying, Prev: Utilities, Up: Top 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 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. * Menu: * Error values:: A list of all error values used. * Error strings:: How to get a descriptive string from a value. File: gcrypt.info, Node: Error values, Next: Error strings, Up: Error Handling Error values ============ Errors are return as an `int' Except for the EOF and No_Error cases an application should always use the constants. Possible values are: `GCRYERR_EOF' This value indicates the end of a list, buffer or file and is defined to have the value `-1'. `GCRYERR_SUCCESS' This value indicates success. The value of this error is `0'. `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 seperate error value for this type of problem. File: gcrypt.info, Node: Error strings, Prev: Error values, Up: Error Handling Error strings ============= - Function: const char * gcry_strerror (int ERR) The function `gcry_strerror' returns a pointer to a statically allocated string containing a description of the error with the error value ERR. This string can be used to output a diagnostic message to the user. 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You can do so by permitting redistribution under these terms (or, alternatively, under the terms of the ordinary General Public License). To apply these terms, attach the following notices to the library. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found. ONE LINE TO GIVE THE LIBRARY'S NAME AND AN IDEA OF WHAT IT DOES. Copyright (C) YEAR NAME OF AUTHOR This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA. Also add information on how to contact you by electronic and paper mail. You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the library, if necessary. Here is a sample; alter the names: Yoyodyne, Inc., hereby disclaims all copyright interest in the library `Frob' (a library for tweaking knobs) written by James Random Hacker. SIGNATURE OF TY COON, 1 April 1990 Ty Coon, President of Vice That's all there is to it!