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June 29, 2005

Lovers' Secret Discourse and German U-Boats

When we were eleven years old, my best friend and I came up with a set of code words for important spy-like discussions (no, this was not related to my detective agency). For example, "orange peels" meant "my parents are listening, I cannot respond to you at this time". Little did we know, we had invented our own, albeit ultra-simple, form of cryptography.

Passing secret messages is a very old concept. The Rosetta Stone, with its hieroglyphic, demotic, and Greek texts, is an excellent example from ancient times. The Kama Sutra (an ancient Indian text written somewhere between 100 and 600 AD) recommended using code in order for lovers to communicate without fear of discovery. Later the Catholic Church used coded messages to help ensure their religious and political power throughout Europe. Thomas Jefferson invented a cipher machine, which the founding fathers used during the American Revolution to secure their mail from being read. Napoleon also used fairly sophisticated ciphers. The list goes on and on, however most of these coded messages could be deciphered more like word puzzles than math problems. Most coded messages could be decrypted by individuals, given time and enough data. These early codes were "easy" to break because of a couple of reasons:

• Decoding wasn't all or nothing. Often, there was an opportunity to decode parts of the message, even if you couldn't deduce the whole thing
• Decoding was a reducing problem. The more you had decoded, the easier the rest of the decoding work became.
• Key-Value pairs did not mutate. If the letter 'A' (the key) stood for the letter 'X' (the value), then this would hold true for every instance of the letter 'A' as long as the crib-sheet was used.
• Information traveled slowly, and key-value crib-sheets did not change often.

It wasn't really until the World Wars that cryptography became more of a mathematical/machine problem and less of a word teaser puzzle. All the statements above suddenly could not be counted on. New encryption devices, especially those with rotors like the German Enigma machine, changed everything. The three rotor Enigma machine had an initial configuration which would dictate the final encoded message. There were 10^114 possible initial configurations, and the initial config used changed daily or more frequently. And guess what? If you determined that A->S for the first letter, that did not mean that the second A was also an S, it could just as easily have been a B. So for example, you could encode AAAAAA and the Enigma would make that LFDYNF. Lastly, the German U-Boats had a different Enigma decide with four rotors instead of three, making the codes significantly harder to decipher.

Besides seeing the several entertaining movies about the Enigma machine like Enigma, based on the book by Robert Harris, and U-571, I have had the pleasure of seeing two real German Enigma machines up close and personal. The first I saw at the Jersey War Tunnels Museum in the Channel Islands, and the second one I saw at the new International Spy Museum in Washington, DC. Nowadays, a real Enigma machine goes for more than $25,0000 at auction. The picture above is from the CIA, but when I find my pictures of the Jersey Enigma Machine, I'll post them, too.

Shane was playing at work today with a Paper Enigma machine he found directions for on the web. He's got a nice little write-up on it on his blog here.

There's also a Flash Enigma Machine available online, which is a bit slow but wins out for any length of message.

WOKELCATF! (I-II-III, LED)

Posted by sorsha at June 29, 2005 6:09 PM