The Enigma algorithm is a encryption method that was developed
(I believe) by the Germans in WWII. It went a little something
like this: When a letter was typed on the keyboard of the Enigma
machine, it was first sent through the first rotor, which would
shift the letter according to its present setting. The new
letter would then pass through the second rotor, where it would
be replaced by a substitution according to the present setting
of the second rotor. This new letter would in turn pass through
the third rotor, again being substituted accordingly. Next, this
new letter would be bounced off of a reflector, and back through
the three rotors in reverse order. The trick that made Enigma so
powerful for its time though, was the spinning of the rotors. As
the plain text letter passed through the first rotor, the first
rotor would rotate one position. The other two rotors would
remain stationary until the first rotor had rotated 26 times
(the number of letters in the alphabet and therefore, one full
rotation).