Code makers and breakers of WWII

Every day, the order of the wired rotors inside the Enigma machine was switched according to a keylist — thus making it difficult for an enemy to figure out its complicated pattern. Until the creation of the Navy Bombe, the Enigma's secret messages were unbreakable without a keylist.

In fact, one version of the Enigma was considered by Germany to be completely unbreakable, as it could be set up in any one of a vast number of ways (two times 10 to the 145th power), each of which would encrypt a plain-text message differently. More than 60 years after the war ended, a distributed-computing project succeeded in deciphering a message encoded with the four-rotor machine.