CRYPT(1)                                                 CRYPT(1)

     NAME
          crypt - encode/decode

     SYNOPSIS
          crypt [ password ]

     DESCRIPTION
          Crypt reads from the standard input and writes on the stan-
          dard output.  The password is a key that selects a particu-
          lar transformation.  If no password is given, crypt demands
          a key from the terminal and turns off printing while the key
          is being typed in.  Crypt encrypts and decrypts with the
          same key:

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

          will print the clear.

          Files encrypted by crypt are compatible with those treated
          by the editor ed 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 cleartext can become visible must be minimized.

          Crypt 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.  How-
          ever, if keys are restricted to (say) three lower-case let-
          ters, then encrypted files can be read by expending only a
          substantial fraction of five minutes of machine time.

          Since the key is an argument to the crypt command, it is
          potentially visible to users executing ps(1) or a deriva-
          tive.  To minimize this possibility, crypt takes care to
          destroy any record of the key immediately upon entry.  No
          doubt the choice of keys and key security are the most vul-
          nerable aspect of crypt.

     FILES
          /dev/tty for typed key

     CRYPT(1)                                                 CRYPT(1)

     SEE ALSO
          ed(1), makekey(8)

     BUGS
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