The latter command decrypts the file and prints the clear version.
Files encrypted by are compatible with those treated by the editor in encryption mode (see ed(1)).
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.
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; i.e., to take a substantial fraction of a second to compute. However, if keys are restricted to, for example, three lowercase 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 command, it is potentially visible to users executing the or a derivative (see ps(1)). The choice of keys and key security are the most vulnerable aspect of
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Note that the option is the encryption mode of and prompts the user for the same key with which the file was encrypted.
If two or more files encrypted with the same key are concatenated and an attempt is made to decrypt the result, only the the first of the original files is decrypted correctly.