Enigma.

The Enigma machines were used to encrypt and decrypt information.

They were invented after WWI and were first used commercially to encode business information. More complex versions of these machines were used by the German Navy, Army and Airforce to encode and decode their communications before and during WW2. "Plaintext" messages written in the latin alphabet are passed through one Enigma machine to become "ciphertext". Ciphertext alone is meaningless can then be transmitted by an unsecure channel (i.e telephone). The ciphertext would be be decrypted by being passed back through another Enigma machine.

The encipherment method here functions like an "unsteckered" Enigma machine, which is the most simple version of the machine.

It relies on three rotating wheels of letters to make a "polyalphabetic substitution" for each plaintext letter. To encrypt a message on one machine to encrypt and decrypt it on another machine message, the rotors and starting positions must be the same on both machines.

For a wonderful explanation of how these machines work, visit:

• enigma.louisedade.co.uk
• www.counton.org/enigma