crypt(1)                                                 crypt(1)



NAME
     crypt - encodes and decodes passwords

SYNOPSIS
     crypt [password]

ARGUMENTS
     password
          Specifies the password to be encoded or decoded.

DESCRIPTION
     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.  The crypt command encrypts and
     decrypts with the same key:

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

     will print the clear text file, clear.

     Files encrypted by crypt are compatible with those treated
     by both the ed and ex editors 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 security of this scheme should not be relied on, for
     reasons described herein.

     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.  If
     keys are restricted to (for example) three lowercase
     letters, however, encrypted files may 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 immediately upon entry.
     The choice of keys and key security are the most vulnerable
     aspect of crypt.



January 1992                                                    1

crypt(1)                                                 crypt(1)



EXAMPLES
     The command:

        crypt asa < sleeper.c > zzz

     will use the string asa as key to the encryption algorithm
     to encrypt the contents of sleeper.c, and place the
     encrypted output in file zzz.  The file zzz at this point
     will be unreadable.  Note that the original file, sleeper.c,
     remains in readable form.  To obtain a readable printout of
     the file zzz, it could be decoded as follows:

        crypt < zzz

     After the response:

        Enter key:

     the user types in: asa.

LIMITATIONS
     If output is piped to nroff and the encryption key is not
     given on the command line, crypt may leave terminal modes in
     a strange state (see stty(1)).

     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.

NOTES
     This utility is not provided with international
     distributions.

FILES
     /bin/crypt
          Executable file
     /dev/tty
          Terminal device file

SEE ALSO
     ed(1), ex(1), makekey(1), stty(1), vi(1)

     crypt(3C) in A/UX Programmer's Reference











2                                                    January 1992