manpage.txt

密码包

MCRYPT(3)                                               MCRYPT(3)



NAME
       libmcrypt - encryption/decryption library

SYNOPSIS
       [see also mcrypt.h for more information]

DESCRIPTION
       The  libmcrypt  is a data encryption library.  The library
       is thread safe  and  provides  encryption  and  decryption
       functions.   This  version  of  the  library supports many
       encryption algorithms and  encryption  modes.  Some  algo-
       rithms which are supported: SERPENT, RIJNDAEL, 3DES, GOST,
       SAFER+, CAST-256, RC2, XTEA, 3WAY, TWOFISH, BLOWFISH, ARC-
       FOUR, WAKE and more.

       OFB,  CBC,  ECB, nOFB, nCFB and CFB are the modes that all
       algorithms may function.  ECB, CBC, encrypt in blocks  but
       CTR,  nCFB,  nOFB,  CFB  and OFB in bytes (streams).  Note
       that CFB and OFB in the rest of the document represent the
       "8bit  CFB or OFB" mode.  nOFB and nCFB modes represents a
       n-bit OFB/CFB mode, n is used to represent the algorithm's
       block  size.  The library supports an extra STREAM mode to
       include some stream algorithms like WAKE or ARCFOUR.

       In this version of the library all  modes  and  algorithms
       are  modular,  which means that the algorithm and the mode
       is loaded at run-time.  This way you  can  add  algorithms
       and modes faster, and much easier.

       LibMcrypt  includes  the following symmetric (block) algo-
       rithms:

       DES: The traditional DES algorithm designed by IBM and  US
       NSA.   Uses 56 bit key and 64 bit block. It is now consid-
       ered a weak algorithm, due to its small key size  (it  was
       never intended for use with classified data).

       3DES or Triple DES: DES but with multiple (triple) encryp-
       tion. It encrypts the plaintext  once,  then  decrypts  it
       with  the second key, and encrypts it again with the third
       key (outer cbc mode used for cbc).  Much better than  tra-
       ditional  DES  since the key is now 168 bits (actually the
       effective key length is 112 bits due to  the  meet-in-the-
       middle attack).

       CAST-128:  CAST  was  designed in Canada by Carlisle Adams
       and Stafford Tavares.  The original algorithm used a 64bit
       key and block. The algorithm here is CAST-128 (also called
       CAST5) which has a 128bit key and 64bit block size.

       CAST-256: CAST-256 was designed by Carlisle Adams. It is a
       symmetric  cipher  designed  in  accordance  with the CAST
       design procedure. It is an extention of the CAST-128, hav-
       ing a 128 bit block size, and up to 256 bit key size.

       xTEA:  TEA stands for the Tiny Encryption Algorithm. It is
       a feistel cipher designed by  David  Wheeler  &  Roger  M.
       Needham.   The original TEA was intended for use in appli-
       cations where code size is at a premium, or  where  it  is
       necessary  for  someone to remember the algorithm and code
       it on an arbitrary machine at a later time.  The algorithm
       used  here  is  extended TEA and has a 128bit key size and
       64bit block size.

       3-WAY: The 3way algorithm designed by Joan Daemen. It uses
       key and block size of 96 bits.

       SKIPJACK: SKIPJACK was designed by the US NSA. It was part
       of the ill-fated "Clipper"  Escrowed  Encryption  Standard
       (EES) (FIPS 185) proposal. It operates on 64bit blocks and
       uses a key of 80 bits. SKIPJACK is  provided  only  as  an
       extra module to libmcrypt.

       BLOWFISH:   The   Blowfish  algorithm  designed  by  Bruce
       Schneier. It is better and faster than DES. It can  use  a
       key up to 448 bits.

       TWOFISH:  Twofish  was  designed  by  Bruce Schneier, Doug
       Whiting, John Kelsey, Chris Hall, David Wagner  for  Coun-
       terpane  systems.  Intended to be highly secure and highly
       flexible. It uses a 128bit block size and 128,192,256  bit
       key size.  (Twofish is the default algorithm)

       LOKI97:  LOKI97  was  designed  by  Lawrie Brown and Josef
       Pieprzyk. It has a 128-bit block length and a  256bit  key
       schedule,  which  can be initialized using 128, 192 or 256
       bit keys. It has  evolved  from  the  earlier  LOKI89  and
       LOKI91  64-bit  block  ciphers,  with  a  strenghtened key
       schedule and a larger keyspace.

       RC2: RC2 (RC stands for Rivest Cipher) was designed by Ron
       Rivest. It uses block size of 64 bit and a key size from 8
       to 1024 bits. It is optimized  for  16bit  microprocessors
       (reflecting its age). It is described in the RFC2268.

       ARCFOUR: RC4 was designed by Ron Rivest. For several years
       this algorithm was considered a trade secret  and  details
       were  not  available. In September 1994 someone posted the
       source code in the cypherpunks mailing list. Although  the
       source  code is now available RC4 is trademarked by RSADSI
       so this algorithm is not included in the mcrypt  distribu-
       tion. A compatible cipher named ARCFOUR is included in the
       mcrypt distribution. It is a stream cipher and has a maxi-
       mum key of 2048 bits.

       RC6:  RC6  was  designed  by  Ron  Rivest for RSA labs. In
       mcrypt it uses block size of 128 bit and  a  key  size  of
       128/192/256  bits.   Refer  to RSA Labs and Ron Rivest for
       any copyright, patent or license issues for the RC6  algo-
       rithm.  RC6  is  provided only as an extra module to libm-
       crypt.

       RIJNDAEL: Rijndael is a block  cipher,  designed  by  Joan
       Daemen and Vincent Rijmen as a candidate algorithm for the
       AES. The cipher  has  a  variable  block  length  and  key
       length.  Rijndael can be implemented very efficiently on a
       wide range of processors and in hardware.  The  design  of
       Rijndael  was  strongly  influenced  by  the design of the
       block cipher Square.  There exist three versions  of  this
       algorithm,  namely:  RIJNDAEL-128 (the AES winner) , RIJN-
       DAEL-192 , RIJNDAEL-256 The  numerals  128,  192  and  256
       stand for the length of the block size.

       MARS:  MARS is a 128-bit block cipher designed by IBM as a
       candidate for the Advanced Encryption Standard.  Refer  to
       IBM  for  any  copyright, patent or license issues for the
       MARS algorithm. MARS is provided only as an  extra  module
       to libmcrypt.

       PANAMA:  PANAMA is a cryptographic module that can be used
       both as a cryptographic hash  function  and  as  a  stream
       cipher. It designed by Joan Daemen and Craig Clapp. PANAMA
       (the stream cipher) is included in libmcrypt.

       WAKE: WAKE stands for Word Auto Key Encryption, and is  an
       encryption  system  for  medium speed encryption of blocks
       and of high security.   WAKE  was  designed  by  David  J.
       Wheeler.  It  is intended to be fast on most computers and
       relies on repeated table use  and  having  a  large  state
       spece.

       SERPENT:  Serpent  is  a  128-bit block cipher designed by
       Ross Anderson, Eli Biham and Lars Knudsen as  a  candidate
       for  the  Advanced  Encryption Standard.  Serpent's design
       was limited to well understood mechanisms, so  that  could
       rely on the wide experience of block cipher cryptanalysis,
       and achieve the highest practical level of assurance  that
       no  shortcut  attack  will  be found. Serpent has twice as
       many rounds as are necessary, to block all currently known
       shortcut  attacks.  Despite  these  exacting  design  con-
       straints, Serpent is faster than DES.

       IDEA: IDEA stands for International Data Encryption  Algo-
       rithm  and was designed by Xuejia Lai and James Massey. It
       operates on 64bit blocks and  uses  a  key  of  128  bits.
       Refer  to  Ascom-Tech  AG  for  any  copyright,  patent or
       license issues for the IDEA algorithm.  IDEA  is  provided
       only as an extra module to libmcrypt.

       ENIGMA  (UNIX  crypt):  A one-rotor machine designed along
       the lines of Enigma  but  considerable  trivialized.  Very
       easy  to  break  for  a  skilled  cryptanalist.  I suggest
       against using it. Added just for completeness.

       GOST: A former soviet union's algorithm.  An  acronym  for
       "Gosudarstvennyi Standard" or Government Standard. It uses
       a 256 bit key and a 64 bit block.
        The S-boxes used here are described in the Applied  Cryp-
       tography  book  by  Bruce  Schneier.  They were used in an
       application for the Central Bank of  the  Russian  Federa-
       tion.
        Some  quotes  from  gost.c: The standard is written by A.
       Zabotin (project leader), G.P. Glazkov, and  V.B.  Isaeva.
       It  was  accepted and introduced into use by the action of
       the State Standards Committee of the USSR on 2  June  1989
       as  No.  1409.  It was to be reviewed in 1993, but whether
       anyone wishes to take on this obligation from the USSR  is
       questionable.
        This code is based on the 25 November 1993 draft transla-
       tion by Aleksandr Malchik, with Whitfield Diffie,  of  the
       Government  Standard of the U.S.S.R. GOST 28149-89, "Cryp-
       tographic  Transformation  Algorithm",  effective  1  July
       1990.   ([e-mail])  Some  details have
       been cleared up by the paper "Soviet Encryption Algorithm"
       by  Josef  Pieprzyk and Leonid Tombak of the University of
       Wollongong, New South Wales.  (josef/[e-mail])

       SAFER: SAFER (Secure And Fast  Encryption  Routine)  is  a
       block  cipher  developed by Prof. J.L. Massey at the Swiss
       Federal Institute of Technology.  There  exist  four  ver-
       sions  of this algorithm, namely: SAFER K-64 , SAFER K-128
       , SAFER SK-64 and SAFER SK-128.  The numerals 64  and  128
       stand  for the length of the user-selected key, 'K' stands
       for the original key schedule  and  'SK'  stands  for  the
       strengthened  key  schedule  (in  which some of the "weak-
       nesses" of the original key schedule have  been  removed).
       In mcrypt only SAFER SK-64 and SAFER SK-128 are used.

       SAFER+:  SAFER+  was  designed by Prof. J.L. Massey, Prof.
       Gurgen H. Khachatrian  and  Dr.  Melsik  K.  Kuregian  for
       Cylink.  SAFER+  is  based on the existing SAFER family of
       ciphers and provides for a block size of 128bits and  128,
       192 and 256 bits key length.



       A short description of the modes supported by libmcrypt:

       STREAM:  The  mode  used with stream ciphers. In this mode
       the keystream from the cipher is XORed with the plaintext.
       Thus you should NOT ever use the same key.

       ECB: The Electronic CodeBook mode. It is the simplest mode
       to use with a block cipher. Encrypts each  block  indepen-
       dently. It is a block mode so plaintext length should be a
       multiple of blocksize (n*blocksize).

       CBC: The Cipher Block Chaining mode. It is better than ECB
       since  the  plaintext  is XOR'ed with the previous cipher-
       text. A random block should be placed as the  first  block
       (IV) so the same block or messages always encrypt to some-
       thing different. It is a block mode  so  plaintext  length
       should be a multiple of blocksize (n*blocksize).

       CFB:  The  Cipher-Feedback Mode (in 8bit). This is a self-
       synchronizing  stream  cipher  implemented  from  a  block
       cipher.  This  is  the  best  mode  to  use for encrypting
       strings or streams. This mode requires an IV.

       OFB: The Output-Feedback Mode (in 8bit). This  is  a  syn-
       chronous stream cipher implemented from a block cipher. It
       is intended for use  in  noisy  lines,  because  corrupted
       ciphertext blocks do not corrupt the plaintext blocks that
       follow. Insecure (because used in 8bit mode) so it is rec-
       ommended not to use it. Added just for completeness.

       nOFB: The Output-Feedback Mode (in nbit). n Is the size of
       the block of the algorithm. This is a  synchronous  stream
       cipher implemented from a block cipher. It is intended for
       use in noisy lines, because corrupted ciphertext blocks do
       not  corrupt  the  plaintext blocks that follow. This mode
       operates in streams.

       nCFB: The Cipher-Feedback Mode (in nbit). n Is the size of
       the  block  of the algorithm. This is a self synchronizing
       stream cipher implemented from a block cipher.  This  mode
       operates in streams.

       CTR: The Counter Mode. This is a stream cipher implemented
       from a block cipher. This mode uses the cipher to  encrypt
       a  set of input blocks, called counters, to produce blocks
       that will be XORed with the plaintext.  In  libmcrypt  the
       counter is the given IV which is incremented at each step.
       This mode operates in streams.

       Error Recovery in these modes: If  bytes  are  removed  or
       lost  from  the  file  or  stream in ECB, CTR, CBC and OFB
       modes, are impossible to recover, although  CFB  and  nCFB
       modes  will recover. If some bytes are altered then a full
       block of plaintext is affected in ECB, nOFB and CTR modes,
       two blocks in CBC, nCFB and CFB modes, but only the corre-
       sponding byte in OFB mode.


       Encryption can be done as follows:

       A call to function: MCRYPT mcrypt_module_open( char *algo-
       rithm,   char*  algorithm_directory,                 char*
       mode, char* mode_directory);

       This function associates the algorithm and the mode speci-
       fied.   The  name  of  the algorithm is specified in algo-
       rithm, eg "twofish", and the  algorithm_directory  is  the
       directory  where the algorithm is (it may be null if it is
       the default). The same applies for the mode.  The  library
       is closed by calling mcrypt_module_close(), but you should
       not call that function if mcrypt_generic_end()  is  called
       before.   Normally it returns an encryption descriptor, or
       MCRYPT_FAILED on error.

       A call to function: int  mcrypt_generic_init(  MCRYPT  td,
       void *key, int lenofkey, void *IV);

       This  function  initializes  all buffers for the specified
       thread The maximum value of lenofkey  should  be  the  one
       obtained  by calling mcrypt_get_key_size() and every value
       smaller than this is legal.  Note that Lenofkey should  be
       specified  in bytes not bits.  The IV should normally have
       the size of the algorithms block size, but you must obtain
       the  size  by calling mcrypt_get_iv_size().  IV is ignored
       in ECB. IV MUST exist in CFB, CBC, STREAM,  nOFB  and  OFB
       modes.  It needs to be random and unique (but not secret).
       The same IV must be used for encryption/decryption.  After
       calling  this  function  you  can  use  the descriptor for
       encryption or decryption (not both).  Returns  a  negative
       value on error.

       To encrypt now call:

       int mcrypt_generic( MCRYPT td, void *plaintext, int len);

       This is the main encryption function. td is the encryption
       descriptor returned by mcrypt_generic_init(). Plaintext is
       the  plaintext  you  wish to encrypt and len should be the
       length (in bytes)  of  the  plaintext  and  it  should  be
       k*algorithms_block_size  if  used in a mode which operated
       in blocks (cbc, ecb, nofb), or whatever when used  in  cfb
       or ofb which operate in streams. The plaintext is replaced
       by the ciphertext. Returns 0 on success.

       To decrypt you can call:

       int mdecrypt_generic( MCRYPT  td,  void  *ciphertext,  int
       len);

       The  decryption  function.  It  is  almost  the  same with
       mcrypt_generic.  Returns 0 on success.

       When you're finished you should call:

       int mcrypt_generic_end( MCRYPT td);

       This  function  terminates  encryption  specified  by  the
       encryption   descriptor  (td).   Actually  it  clears  all
       buffers, and closes all the modules used.  Returns a nega-
       tive  value  on  error.  This function is deprecated.  Use
       mcrypt_generic_deinit() and mcrypt_module_close() instead.

       int mcrypt_generic_deinit( MCRYPT td);

       This  function  terminates  encryption  specified  by  the
       encryption  descriptor  (td).   Actually  it  clears   all
       buffers.  The difference with mcrypt_generic_end() is that
       this function does not close the modules  used.  Thus  you
       should use mcrypt_module_close().  Using this function you
       gain in speed if you use  the  same  modules  for  several
       encryptions.  Returns a negative value on error.

       int mcrypt_module_close( MCRYPT td);

       This  function  closes  the modules used by the descriptor
       td.