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CRYPT(1)                    General Commands Manual                   CRYPT(1)



NAME
       crypt - encode or decode a file

SYNOPSIS
       crypt [ password ]

DESCRIPTION
       crypt  encrypts  and decrypts the contents of a file.  crypt reads from
       the standard input and writes on the standard output.  The password  is
       a  key  that  selects  a  particular 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:

              example% crypt key <&lt;clear.file >&gt;encrypted.file
              example% crypt key <&lt;encrypted.file | pr

       will print the contents of clear.file.

       Files encrypted by crypt are compatible with those treated by the  edi-
       tors ed(1), ex(1) and vi(1) in encryption mode.

       The  security  of encrypted files depends on three factors:  the funda-
       mental 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 widely known, thus crypt provides minimal security.

       The transformation of a key into the internal settings of  the  machine
       is  deliberately  designed to be expensive, that is, to take a substan-
       tial 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.

       Since the key is an argument to the crypt command,  it  is  potentially
       visible  to users executing ps(1) or a derivative command.  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 vulnerable aspect of crypt.

FILES
       /dev/tty            for typed key

SEE ALSO
       des(1), ed(1), ex(1), ps(1), vi(1), makekey(8)

RESTRICTIONS
       This program is not available on software shipped outside the U.S.



                               9 September 1987                       CRYPT(1)