Why enigma machine was used

Nora McGreevy is a daily correspondent for Smithsonian. She can be reached through her website, noramcgreevy. A team of divers found this rusted—but still recognizable—Enigma cipher machine at the bottom of the Baltic Sea. World Wildlife Fund Last month, German divers scanning the Baltic seafloor for abandoned fishing nets happened upon a rare piece of history: a strange contraption with keys and a rotor, rusted and covered in algae but relatively intact. A team of German divers poses next to the Enigma cipher machine.

Straddling the border between mechanical and electrical, Enigma looked from the outside like an oversize typewriter. Enter the first letter of your message on the keyboard and a letter lights up showing what it has replaced within the encrypted message. Inside the box, the system is built around three physical rotors.

Each takes in a letter and outputs it as a different one. The board lights up to show the encrypted output, and the first of the three rotors clicks round one position — changing the output even if the second letter input is the same as the first one.

Adding to the scrambling was a plugboard, sitting between the main rotors and the input and output, which swapped pairs of letters.

The messages sent out each day used a different password, and discovering this password permitted the messages to be read. The machines used in the decoding work were called Bombes. They could only solve one problem, so were not really true computers. The information received from deciphered material was codenamed ULTRA, as the fact that messages could be deciphered had to be closely guarded to prevent the encryption methods being changed.

This ability to decipher German military communications is often thought to have helped bring the war to a swifter end, although decades of secrecy delayed the recognition of the work carried out at Bletchley Park. This short video demonstrates how a Swiss Enigma machine translates messages into cipher, and how this can then be deciphered.

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