CRYPT(1) User Commands CRYPT(1)

NAME

crypt - encode or decode a file

SYNOPSIS

crypt [password]

DESCRIPTION

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.

FILES

/dev/tty
for typed key

SEE ALSO

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

March 8, 2005 CRYPT(1)