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We have been very happy to see all the press and support we've gotten for the National Museum of Computing at Bletchley Park. The need has not gone away, so please if you haven't gotten one of our great t-shirts, do so. If you don't wear t-shirts, please contribute a little to help save history. The donation is made via PayPal, so it can be any amount you choose.

In my last post, I gave an Enigma puzzle with a message to decrypt. Since it's been a few weeks, I'll tell you how to solve it.

The hard part, as I said, is finding a good Enigma simulator. There are many of them around, and some of them aren't very good. The one I used was Terry Long's simulator for the Mac, which you can find at http://www.terrylong.org/. It's a beautiful work of software art as well as a good simulator.

The settings that I gave are closely related to the way settings were distributed. The first thing you have to do is pick the right three of five wheels, which is easy, because the settings tell you that. The next thing is to set the ring on each rotor. Sometimes these were marked with numbers, sometimes with letters. If the emulator you had numbers, you had to set them to 7-13-25 instead of GMY. Lastly, you had to set up the plugboard, connecting the wires in pairs.

Some Enigma simulators (including Terry Long's) have another setting for the Reflector type. The reflector is a basic setting of a model of Engimas, and there were many, many variants of the Enigma. If you had an option, you had to guess on this, but nearly every simulator had the "B" reflector as its default, and that's what this puzzle used.

The hard part was knowing what to do with the cryptic "DHO GXS". They never sent the rotor starting positions (which is the cryptographic key) in the clear, they used this other way to send it. You get the real rotor settings by setting the rotors to the first triplet, DHO, and typing in the second triplet, GXS. That gives you the three letters RLP, and *that* is what you set the three rotors to.

That's tricky, but many problems have both a straightforward solution and what I call the Gordian Knot solution, the one where you untie the knot by cutting the rope. It's blunt but effective. The Gordian Knot solution to this is to search the web for "DHO GXS". If you use Google, the very first page that comes up is Tony Sale's instruction page on how to work an Enigma.

Tony Sale is the leader of the Colossus rebuild project, and has many very good pages on WWII cryptography. He was also the technical consultant on the film, "Enigma," and that page is his instructions on how to use an Enigma. He uses as his example the message that Kate Winslet's character used in the movie. He tells you how to set up an Enigma with the settings that he devised for that scene of the movie.

And those settings are the exact settings I used for this puzzle. One of the subtle goals I had for the puzzle was that if you in trying to solve the puzzle thought, "Heck, how am I going to learn to use an Enigma properly?" a few web searches would bring you to the page I found when I needed to do the exact thing to create the puzzle. And whose page better than that of Tony Sale's? This is also why I stole Tony's settings. I knew they'd work, and I knew that whatever complaints people had about how they were expressed, if you started putting those settings into a web search, you'd end up at Tony.

The difference was only in the message. The message I gave had the ciphertext of DBPTU YRQJB HWCQW CHAEV HMOII PGPDU OAKYK FFSUT BVFDH UHOAG QWRCA and using Tony's settings, you get the plaintext of THEXG EESEX THATX LAIDX THEXG OLDEN XEGGS XBUTX NEVER XCACK LEDXX or removing the Xs that separate the words, THE GEESE THAT LAID THE GOLDEN EGGS BUT NEVER CACKLED. This is a quote from Winston Churchill, who said that in reference to the cryptanalysts ate Bletchley Park.

I'd like to thank the people who helped me with the puzzle, who include Lauren Ames, Rozanne Bonavito, Hal Finney, Bryan Gillson, Terry Long, Tim Matthews, Mike Messick, Vinnie Moscaritolo, Cat Okita, Blake Ramsdell, Bruce Schneier, and John Wojtacha. I'd like to apologize to the people I should have thanked and forgot to mention.

In my next post, I'll talk about the hard puzzle -- the one on the t-shirt that was encrypted by the Lorentz machine and cryptanalyzed with Colossus.

Jon

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