Early 1940: British police listening for radio transmissions from German spies within the UK pick up weird signals, and pass them to Bletchley Park
, the United Kingdom's main decryption establishment in WWII. The source of these German messages is an unknown machine, which the Brits dub Tunny
(10 minute video with Tony Sale
describing the Tunny). August 30, 1941: German operators send two very similar messages with the same key, providing insight into the encryption scheme. By January 1942, British cryptographers deduced the workings of the German code machines, sight unseen. The British were able to create their own Tunny emulators to decrypt messages sent by German High Command. After the war, these and other British code-breaking and emulating machines were demolished and/or recycled for parts and their blueprints destroyed, leaving a hole in the history of the British WWII code breaking. Efforts to rebuild the British Tunny emulator started in the 1990s, and quite recently a Tunny emulator replica was completed
The German military had a number of different encrypted communications systems
, from the relatively simple modified German military version
of the commercially-available Enigma machine
(Google Quickview / PDF
). The more complex systems were based on teleprinters
The Germans had three different types of teleprinter cipher machines
(Google Quickview / PDF
) : three models of the Lorenz system, dubbed Tunny by the British; various models of the Siemens & Halske Schlüsselfernschreibmaschine (SFM), named Sturgen by the British; and the Siemens T43, which may have been the unbroken system nicknamed Thrasher. Tunny was used by the German army, while Sturgen was used by the navy and air force. The German nickname for the special teleprinter equipment was Sägefisch
(sawfish), which is the source of the Fish nickname in England, and the subsequent fish-related nicknames for specific systems.
When the British first found the "fish" messages, they realized these communications were quite important messages. The first break in Tunny came on August 30, 1941
, when a German operator missed a message on first transmission and asked, in plaintext, that the message be re-sent. The key setting was the same and the message was largely similar, allowing British cryptographers to figure out the operations of the cipher machine without seeing it. About five months later, the Tunny emulator was built, allowing cipher text to be decrypted, once the decoding settings were figured out by hand.
The first attempt to speed up the process was Heath Robinson
, a mechanical method of figuring out the decoder settings. The second is the world's first programmable electronic computer, Colossus
, and made by Thomas Harold Flowers
) at the Dollis Hill Post Office Research Station
. A number of Colossi were built, and all of these machines were dismantled at the end of the war, to guard against their secrets becoming known.
By finding scraps of information and picking the memories of those who made and worked with the machines With the re-creation of the Tunny emulator, Bletchley Park once again has a complete set of re-created decrypting machines
(photos of the exhibit at The National Museum of Computing
, itself located at Bletchley Park
More interesting details and rabbit trails:
* The Fish and I
, Professor William T. Tutte
's paper on FISH, as presented at the opening ceremony of Centre for Applied Cryptographic Research at the University of Waterloo
. This paper is just one of the many fascinating features at Frode Weierud's CryptoCellar
* WW II Codes and Ciphers
, Tony Sale's website on the Colossus and Tunny rebuild efforts, Enigma, and other related topics.
* An introduction to Bletchley Park
, a 2008 MetaFilter post.