Comment by mathieuh | Hacker News Reader

Comment by mathieuh | Hacker News Reader

I'm not sure of the prior history, which may affect my appreciation for it, but as far as I know, what happened with Colossus was that they were aware the cipher seeds changed each day, and they obtained an Enigma machine so they could decipher Enigma codes, it was the fact there was a reliance on intercepting the day’s seeds, or having a spy/double agent leak them which meant cracking Enigma messages was usefully impossible within the timeframe in which military strategies could be formulated and altered.

So Colossus brute-forced every combination of Enigma symbols and seeds until it got something that made sense.

Colossus did this in hours, instead of the weeks waiting for code breakers with brain-power and persistence alone, and to my knowledge this was the first application of computers as we recognise them today.

I find it amazing that Turing sat and thought to himself, in the 1940s, "I bet I can make a machine that does this", and built the thing, and built it so well it deciphered the codes within the day, before the seeds changed. I'm sure a brute force on paper existed before Colossus, but Colossus is a stunning, visceral machine to watch.

Seeing Colossus operating is an absolute experience for computerphiles. There's something more soulful (in the laïc sense) in seeing a big wall of spinning disks and tape and reassuring thuds and whirs than in modern solid-state computers.

Small correction, Colossus was designed to break the Lorenz cypher (which was considerably more complex than Enigma). The machine itself was designed by Tommy Flowers (not Turing), who was a post office worker who had previously worked with vacuum tubes and thought it would be possible to build a programmable computer with them. After the war Flowers applied for funding to build a similar machine (Colossus being top secret) and was denied on account of the idea being impractical.

The machine Turing is famous for his work on was Bombe, which was designed to crack Enigma.

Can't edit my comment now that it has children (I think that's how the logic works) so upvoting you for visibility.

I’ve visited the rebuilt Colossus at TNMOC a couple times now. I think the usually turn it on at noon, I like to get there just before and stand there in silence looking up at it, and then listening to the thrum, ker-chunk and whir at it comes to life is like nothing else.

Wasn't it that they could feed in certain known possible letters to cut down on the number of options? Something like, "this encrypted segment is usually the weather so the s is probably the word 'sunny'".

I'm shamefully unsure of how it works exactly, but it's possible they had subroutines that looked for phrases like "weather", "movement", "troops" etc. to try and speed up the brute force.

https://www.youtube.com/watch?v=9HH-asvLAj4

Here's a really good video I've watched before and since forgotten the details of which explains Colossus and its context

Some enigma operators had flourishes that the code-breakers could pick up on. Starting or ending a lot of messages with "Heil Hitler" was also a factor IIRC

Yes this is correct. The resulting ciphertext from Enigma was sent by manual Morse transmission. Morse operators can identify others by thier “hand” which is the Morse equivalent of the sound of your voice in speech.

Earlier in the war the Germans typically sent their call signs in plaintext. Many of the intercept operators in the “Y stations” in the UK became familiar with the “hands” of various German operators. Later in the war the Germans started encrypting their call signs, but Bletchley was generally able to distinguish them by the intercept operator’s familiarity with the “hands” of the German Morse operators.

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