CRYPT(1) General Commands Manual CRYPT(1)
crypt - encode or decode a file
crypt [ password ]
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
example% crypt key <<clear.file >>encrypted.file
example% crypt key <<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.
/dev/tty for typed key
des(1), ed(1), ex(1), ps(1), vi(1), makekey(8)
This program is not available on software shipped outside the U.S.
9 September 1987 CRYPT(1)