crypt(1)

crypt -- encode/decode

Synopsis

crypt [password]

crypt [-k]

Description

crypt reads from the standard input and writes on the standard output. The password is a key that selects a particular transformation. If no argument is given, crypt demands a key from the terminal and turns off printing while the key is being typed in. If the -k option is used, crypt will use the key assigned to the environment variable CrYpTkEy. crypt encrypts and decrypts with the same key:

crypt key < clear > cypher
crypt key < cypher | pr

Files encrypted by crypt are compatible with those treated by the editors ed(1), edit(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 clear text 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 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, 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.

If the key is an argument to the crypt command, it is potentially visible to users executing ps(1) or a derivative. The choice of keys and key security are the most vulnerable aspect of crypt.

Files

/dev/tty for typed key

References

ed(1), edit(1), ex(1), nroff(1bsd), pg(1), ps(1), stty(1), vi(1)

Notices

This command is provided with the Encryption Utilities, which is only available in the United States. If two or more files encrypted with the same key are concatenated and an attempt is made to decrypt the result, only the contents of the first of the original files will be decrypted correctly.

If output is piped to nroff and the encryption key is not given on the command line then do not pipe crypt through pg(1) or any other program that changes the tty settings. Doing so may cause crypt to leave terminal modes in a strange state (see stty(1)).