@(#)crypt.1 6.2 (Berkeley) 07/14/87

.AT 3 crypt - encode/decode crypt [ password ] 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:

crypt key <clear >cypher

crypt key <cypher | pr

will print the clear.

Files encrypted by crypt are compatible with those treated by the editor ed 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 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, i.e. 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. 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.

/dev/tty for typed key ed(1), crypt(3), makekey(8) There is no warranty of merchantability nor any warranty of fitness for a particular purpose nor any other warranty, either express or implied, as to the accuracy of the enclosed materials or as to their suitability for any particular purpose. Accordingly, Bell Telephone Laboratories assumes no responsibility for their use by the recipient. Further, Bell Laboratories assumes no obligation to furnish any assistance of any kind whatsoever, or to furnish any additional information or documentation.