


      CRYPT(3C)                   (UNIX 5.0)                  CRYPT(3C)



      NAME
           crypt, setkey, encrypt - generate DES encryption

      SYNTAX
           char *crypt (key, salt)
           char *key, *salt;

           void setkey (key)
           char *key;

           void encrypt (block, edflag)
           char *block;
           int edflag;

      DESCRIPTION
           Crypt is the password encryption function.  It is based on
           the NBS Data Encryption Standard (DES), with variations
           intended (among other things) to frustrate use of hardware
           implementations of the DES for key search.

           Key is a user's typed password.  Salt is a two-character
           string chosen from the set [a-zA-Z0-9./]; this string is
           used to perturb the DES algorithm in one of 4096 different
           ways, after which the password is used as the key to encrypt
           repeatedly a constant string.  The returned value points to
           the encrypted password.  The first two characters are the
           salt itself.

           The setkey and encrypt entries provide (rather primitive)
           access to the actual DES algorithm.  The argument of setkey
           is a character array of length 64 containing only the
           characters with numerical value 0 and 1.  If this string is
           divided into groups of 8, the low-order bit in each group is
           ignored; this gives a 56-bit key which is set into the
           machine.  This is the key that will be used with the above
           mentioned algorithm to encrypt or decrypt the string block
           with the function encrypt.

           The argument to the encrypt entry is a character array of
           length 64 containing only the characters with numerical
           value 0 and 1.  The argument array is modified in place to a
           similar array representing the bits of the argument after
           having been subjected to the DES algorithm using the key set
           by setkey.  If edflag is zero, the argument is encrypted; if
           non-zero, it is decrypted.

      SEE ALSO
           login(1), passwd(1), getpass(3C), passwd(4).

      BUGS
           The return value points to static data that are overwritten
           by each call.



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