crypt - encode/decode
crypt key << input.File >> output.File
The crypt command reads from the standard input and writes on the standard
output. You must supply a key which 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.
Files encrypted by crypt are compatible with those treated by the ed, ex
and vi 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, and sneak paths by which keys or clear text can become visible
must be minimized.
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, for example, to take a substantial
fraction of a second to compute. However, if keys are restricted to three
lowercase letters, then encrypted files can be read by expending only a
substantial fraction of five minutes of machine time.
Since the key you choose is an argument to the crypt command, it is poten-
tially visible to users executing the ps command or a derivative. To
minimize this possibility, crypt destroys any record of the key immediately
upon entry. The most vulnerable aspect of crypt is the choice of keys and
The following examples use KEY as the key to encrypt and decrypt files.
The first example encrypts the file plain.File, naming the resulting
encrypted file crypt.File. The second example decrypts the file
crypt.File, naming the resulting decrypted file decrypt.File. The third
example prints the encrypted file in clear text.
$ crypt KEY < plain.File > crypt.File
$ crypt KEY < crypt.File > decrypt.File
$ crypt KEY < crypt.File | pr
/dev/tty for typed key
ed(1), ex(1), vi(1), crypt(3), makekey(8)