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 potentially 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 key security.
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
for typed key
Commands: ed(1), ex(1), vi(1), makekey(8)
Functions: crypt(3)
crypt(1)
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