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CRYPT(1)                    General Commands Manual                   CRYPT(1)

       crypt - encode/decode

       crypt [ password ]

       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:

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

       will print the clear.

       Files  encrypted by crypt are compatible with those treated by the edi-
       tor ed in encryption mode.

       The security of encrypted files depends on three factors: the fundamen-
       tal  method  must be hard to solve; direct search of the key space must
       be infeasible; `sneak paths' by which keys or cleartext can become vis-
       ible 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.  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.  To minimize this
       possibility, crypt takes care to destroy any record of the key  immedi-
       ately upon entry.  No doubt the choice of keys and key security are the
       most vulnerable aspect of crypt.

       /dev/tty for typed key

       ed(1), makekey(8)

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