ROTOR MACHINES & Steganography

Multiple stages of encryption can produce an algorithm that is significantly more difficult to cryptanalyze. This is as true of substitution ciphers as it is of transposition ciphers. The most important application of the principle of multiple stages of encryption was a class of systems known as ROTOR MACHINES. The most famous example is the German Enigma machine. 'Steganography' is not specifically a technique, but a general practice of concealing a message within other message.