crypt - encode/decode
crypt key < input.File > output.File
The 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, demands a key from the terminal and turns off printing while the key is being typed in. The command encrypts and decrypts with the same key.
Files encrypted by 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 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 command, it is potentially visible to users executing the command or a derivative. To minimize this possibility, destroys any record of the key immediately upon entry. The most vulnerable aspect of 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 naming the resulting encrypted file The second example decrypts the file naming the resulting decrypted 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
ed(1), ex(1), vi(1), crypt(3), makekey(8) delim off