CRYPT(1) User Commands CRYPT(1)


crypt - encode or decode a file


crypt [password]


The crypt utility 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 < clear.file > encrypted.file
example% crypt key < encrypted.file | pr

prints the contents of clear.file.

Files encrypted by crypt are compatible with those treated by the editors
ed(1), ex(1), and vi(1) 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 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 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 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.


for typed key


des(1), ed(1), ex(1), ps(1), vi(1), attributes(7)

March 8, 2005 CRYPT(1)