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NAME    [Toc]    [Back]

     crypt, setkey, encrypt, des_setkey, des_cipher - DES encryption

SYNOPSIS    [Toc]    [Back]

     #include <pwd.h>
     #include <unistd.h>

     char *
     crypt(const char *key, const char *setting);

     setkey(char *key);

     encrypt(char *block, int flag);

     des_setkey(const char *key);

     des_cipher(const  char  *in,  char  *out,  int32_t salt, int

     char *
     bcrypt_gensalt(u_int8_t log_rounds);

     char *
     bcrypt(const char *key, const char *salt);

     char *
     md5crypt(const char *key, const char *salt);

DESCRIPTION    [Toc]    [Back]

     The crypt() function performs password encryption  based  on
the NBS Data
     Encryption  Standard  (DES).  Additional code has been added
to deter key
     search attempts and to use stronger hashing algorithms.

     The first argument to crypt() is a  null-terminated  string,
typically a
     user's typed password.  The second is in one of three forms:
if it begins
     with an underscore (`_') then an extended format is used  in
     both  the key and the setting, as outlined below.  If it begins with a
     string character (`$') and a number then a  different  algorithm is used
     depending  on  the number.  At the moment a `$1' chooses MD5
hashing and a
     `$2' chooses Blowfish hashing; see below for  more  information.

   Extended crypt    [Toc]    [Back]
     The  key  is  divided  into groups of 8 characters (the last
group is nullpadded)
 and the low-order 7 bits of each character (56  bits
per group)
     are  used to form the DES key as follows: the first group of
56 bits becomes
 the initial DES key.  For each additional  group,  the
XOR of the encryption
  of  the  current DES key with itself and the group
bits becomes
     the next DES key.

     The setting is a 9-character array consisting of  an  underscore followed
     by  4  bytes  of iteration count and 4 bytes of salt.  These
are encoded as
     printable characters, 6 bits per character,  least  significant character
     first.   The  values 0 to 63 are encoded as ``./0-9A-Za-z''.
This allows
     24 bits for both count and salt.

   MD5 crypt    [Toc]    [Back]
     For MD5 crypt the version number, salt and the hashed  password are separated
  by  the `$' character.  The maximum length of a password is limited
     by the length counter of the MD5  context,  which  is  about
2**64.  A valid
     MD5 password entry looks like this:


     The  whole  MD5 password string is passed as setting for interpretation.

   Blowfish crypt    [Toc]    [Back]
     The Blowfish version of crypt has 128 bits of salt in  order
to make
     building  dictionaries  of common passwords space consuming.
The initial
     state of the Blowfish cipher is expanded using the salt  and
the password
     repeating  the process a variable number of rounds, which is
encoded in
     the password string.  The maximum  password  length  is  72.
The final Blowfish
 password entry is created by encrypting the string


     with the Blowfish state 64 times.

     The  version  number,  the logarithm of the number of rounds
and the concatenation
 of salt and hashed password are separated by  the
`$' character.
   An  encoded  `8'  would  specify 256 rounds.  A valid
Blowfish password
     looks like this:


     The  whole Blowfish password string is passed as setting for

   Traditional crypt    [Toc]    [Back]
     The first 8 bytes of the key are null-padded, and  the  loworder 7 bits of
     each character is used to form the 56-bit DES key.

     The  setting  is  a  2-character  array of the ASCII-encoded
salt.  Thus only
     12 bits of salt are used.  count is set to 25.

   DES Algorithm    [Toc]    [Back]
     The salt introduces disorder in the DES algorithm in one  of
16777216 or
     4096  possible  ways  (i.e., with 24 or 12 bits: if bit i of
the salt is
     set, then bits i and i+24 are swapped in the DES E-box  output).

     The DES key is used to encrypt a 64-bit constant using count
     of DES.  The value returned is a null-terminated string,  20
or 13 bytes
     (plus null) in length, consisting of the setting followed by
the encoded
     64-bit encryption.

     The  functions  encrypt(),   setkey(),   des_setkey(),   and
des_cipher() provide
     access  to  the  DES algorithm itself.  setkey() is passed a
64-byte array
     of binary values (numeric 0 or 1).  A 56-bit key is extracted from this
     array  by  dividing the array into groups of 8, and ignoring
the last bit
     in each group.  That bit is reserved for a byte parity check
by DES, but
     is ignored by these functions.

     The  block  argument to encrypt() is also a 64-byte array of
binary values.
     If the value of flag is 0, block is encrypted  otherwise  it
is decrypted.
     The result is returned in the original array block after using the key
     specified by setkey() to process it.

     The argument to des_setkey() is a character array of  length
8.  The least
     significant  bit  (the  parity bit) in each character is ignored, and the
     remaining bits are concatenated to form a 56-bit  key.   The
     des_cipher() encrypts (or decrypts if count is negative) the
     stored in the 8 characters at in using abs(3) of count iterations of DES
     and  stores  the  64-bit  result  in the 8 characters at out
(which may be the
     same as in).  The salt specifies perturbations to the DES Ebox output as
     described above.

     The function crypt() returns a pointer to the encrypted value on success,
     and NULL on failure.   The  functions  setkey(),  encrypt(),
     and des_cipher() return 0 on success and 1 on failure.

     The crypt(), setkey(), and des_setkey() functions all manipulate the same
     key space.

SEE ALSO    [Toc]    [Back]

     login(1), passwd(1), blowfish(3), getpass(3), md5(3),  passwd(5)

HISTORY    [Toc]    [Back]

     A  rotor-based  crypt()  function appeared in Version 3 AT&T
UNIX.  The current
 style crypt() first appeared in Version 7 AT&T UNIX.

     This library (FreeSec 1.0) was developed outside the  United
States of
     America  as  an  unencumbered  replacement for the U.S.-only
libcrypt encryption
 library.  Programs linked against the crypt() interface
may be exported
  from  the U.S.A. only if they use crypt() solely for
     purposes and avoid use of the  other  programmer  interfaces
listed above.
     Special  care has been taken in the library so that programs
which only
     use the crypt() interface do not pull in  the  other  components.

AUTHORS    [Toc]    [Back]

     David Burren <davidb@werj.com.au>

BUGS    [Toc]    [Back]

     The  crypt()  function returns a pointer to static data, and
     calls to crypt() will modify the same object.

OpenBSD     3.6                           March      9,      1994
[ Back ]
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