Manual Pages  — ENIGMA

There are several ways to provide the secret key to the program. By default, the program prompts the user on the controlling terminal for the key, using getpass(3). This is the only safe way of providing it.

Alternatively, the key can be provided as the sole command-line argument password when starting the program. Obviously, this way the key can easily be spotted by other users running ps(1). As yet another alternative, enigma can be given the option -k, and it will take the key from the environment variable CrYpTkEy. While this at a first glance seems to be more secure than the previous option, it actually is not since environment variables can also be examined with ps(1). Thus this option is mainly provided for compatibility with other implementations of enigma.

When specifying the option -s, enigma modifies the encryption engine in a way that is supposed to make it a little more secure, but incompatible with other implementations.