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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
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 exe-
cuting 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 secu-
rity are the most vulnerable aspect of crypt.
/dev/tty for typed key
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