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

     void
     setkey(char *key);

     void
     encrypt(char *block, int flag);

     int
     des_setkey(const char *key);

     int
     des_cipher(const char *in, char *out, long salt, int count);

DESCRIPTION

     The crypt() function performs password encryption, based on the NBS Data
     Encryption Standard (DES).  Additional code has been added to deter key
     search attempts.  The first argument to crypt() is a null-terminated
     string, typically a user's typed password.  The second is in one of two
     forms: if it begins with an underscore (``_'') then an extended format is
     used in interpreting both the key and the setting, as outlined below.

   Extended crypt:
     The key is divided into groups of 8 characters (the last group is null-
     padded) and the low-order 7 bits of each 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.

   Traditional crypt:
     The first 8 bytes of the key are null-padded, and the low-order 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.

   Algorithm:
     The salt introduces disorder in the DES algorithm in one of 16777216 or
     4096 possible ways (ie. 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 iterations
     of DES.  The value returned is a null-terminated string, 20 or 13 bytes

     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 function
     des_cipher() encrypts (or decrypts if count is negative) the 64-bits
     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 E-box output
     as described above.

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

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

BUGS

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

HISTORY

     A rotor-based crypt() function appeared in Version 6 AT&T UNIX.  The cur-
     rent 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 encryp-
     tion library.  Programs linked against the crypt() interface may be
     exported from the U.S.A. only if they use crypt() solely for authentica-
     tion 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.

AUTHOR

     David Burren <davidb@werj.com.au>

FreeSec 1.0                      March 9, 1994                     FreeSec 1.0