CRYPT(C)                 XENIX System V                  CRYPT(C)



     Name
          crypt - Encode/decode.

     Syntax
          crypt [ password ]
          crypt [-k]

     Description
          The crypt command reads from the standard input and writes
          to the standard output.  The password is a key that selects
          a particular transformation.  If no argument is given, crypt
          demands a key from the terminal and turns off printing while
          the key is being typed in.  If the -k option is used, crypt
          will use the key assigned to the environment variable
          CRYPTKEY.  The crypt command encrypts and decrypts with the
          same key:

               crypt key <clear >cypher
               crypt key <cypher | pr

          Files encrypted by crypt are compatible with those treated
          by the editors ed(C), edit(C), ex(C), and vi(C) in
          encryption mode.

          The security of encrypted files depends on three factors:
          the fundamental method must be hard to solve; direct search
          of the key space must be infeasible; ``sneak paths'' by
          which keys or clear text can become visible must be
          minimized.

          The crypt command implements a one-rotor machine designed
          along the lines of the German Enigma, but with a 256-element
          rotor.  Methods of attack on such machines are known, but
          not widely; moreover the amount of work required is likely
          to be large.

          The transformation of a key into the internal settings of
          the machine is deliberately designed to be expensive, i.e.,
          to take a substantial fraction of a second to compute.
          However, if keys are restricted to (say) three lower-case
          letters, then encrypted files can be read by expending only
          a substantial fraction of five minutes of machine time.

          If the key is an argument to the crypt command, it is
          potentially visible to users executing ps(C) or a
          derivative.  To minimize this possibility, crypt takes care
          to destroy any record of the key immediately upon entry.
          The choice of keys and key security are the most vulnerable
          aspect of crypt.

     Files
          /dev/tty  for typed key



     Page 1                                           (printed 2/7/91)

     CRYPT(C)                 XENIX System V                  CRYPT(C)



     See Also
          ed(C), edit(C), ex(C), makekey(C), ps(C), stty(C), vi(C)

     Notes
          If two or more files encrypted with the same key are
          concatenated and an attempt is made to decrypt the result,
          only the contents of the first of the original files will be
          decrypted correctly.

          Distribution of the crypt libraries and utilities is
          regulated by the U.S. Government and are not available to
          sites outside of the United States and its territories.
          Because we cannot control the destination of the software,
          these utilities are not included in the standard product.
          If your site is within the U.S. or its territories, you can
          obtain the crypt software through your product distributor
          or reseller.






































     Page 2                                           (printed 2/7/91)