back to article Wannabe infosec kiddies put Enigma Bombe machine to the test

GCHQ historians will this month put the team that rebuilt the British code-cracking Bombe machine to the test in a third Enigma Challenge. The Bombe squad will race against time to break Enigma-encoded messages sent by members of the public and GCHQ’s Historical Section. The exercise is due to take place at The Big Bang Fair, a …

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All enemy comms readable by dawn each day

it took an average of four hours each night to work out the day’s settings on each German military network, most of which were changed at midnight

That is very, very cool.

While it's widely recognised that this won (or at least shortened) the war, it must have been harrowing to have to ignore most of communications with the loss of thousands of lives. All to make sure the Germans kept believing their system was secure.

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Re: All enemy comms readable by dawn each day

"Ultra" intelligence included decrypts of Enigma and Lorenz. And a lot of it was probably not that useful but some would be very useful.

It wouldn't always be the case that the knowledge gained was something that could be acted upon directly. It might confirm suspicions or intelligence from other sources.

In the case of knowledge that could be acted upon, a cover story would be arrange eg in the Battle of the Atlantic, a decrypt of a message indicating a U-boat position could be followed up by an patrol aircraft that could come across the U-boat as if by accident and the Germans would just think the Allies lucky or had more aircraft.

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Re: All enemy comms readable by dawn each day

This is not a criticism of the excellent work done at Bletchley during the war, but in fact the breaking of the German codes was not as impressive as the hacking of the Nazi high command's brains by the Doublecross Committee.

Early in the war it found that MI5 had captured and turned (or shot) ALL of the German spies in Britain, permitting the Doublecross Committee to feed the Germans carefully crafted "intelligence". Ultra allowed MI5 to keep watch as the massive misinformation campaign (Operation Bodyguard) influenced German strategic thinking, causing Hitler to believe the main thrust of Operation Overlord was to be Norway and the Pas de Calais, with a feint into Normandy.

So convinced of this were they that it was weeks before Germans realized that Normandy was the true invasion route.

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Holmes

Re: All enemy comms readable by dawn each day

From what I remember from my cryptography course, the key failure of the enigma machine's use was that the Nazi's decided that they wanted to increase their security by using a random 3 letter, per message, key. They had to transmit the key to the receiver in an insecure channel, so they decided to encrypt the message key with the day key. To make sure that the message key was received, it was transmitted one more time. Meaning for ciphertext LKFUHFFGSFDGSAFS, the 1st character and 4th character map to the same plaintext, the 2nd and 5th, and the 3rd ad 6th chars. Then the remainder of the message was encoded using the message key After generating that mapping from several messages, chains of letter mappings would be used to limit the search space. The number of configurations, including plugboard usage, was 100,391,791,500, but by using this, the plugboard was negated, reducing the space to 105,391 configurations, and with a lookup table, could be used to determine the day key rotor positions. Paired with the tricks mentioned by other commentards, left them with the quick times described.

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Correct me if I'm wrong..

Which will undoubtedly happen should I be, but am I right in thinking the Bombe was spec'd and created in Poland before the war and then reconstructed? I have vague recollections about reading somewhere that the Poles had got hold of an Enigma before the war and were starting to figure out before the invasion and the crypto geeks came to these shores with the plans.

Or am I barking?!

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Re: Correct me if I'm wrong..

I think the Bombe was a design by Turing that improved a design by the Poles, who, as you rightly point out, had done a lot of work on Enigma too.

Enigma started out as a commercial device, and the UK openly bought one in the 20's, but the Mil-Spec device was different so required additional analysis and the Poles were the first to get any significant breakthrough thanks to the French handing over 2 pages of intercepted daily keys.

Then the germans added more rotors, which increased the complexity of the Polish "computer" beyond their resources.

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Re: Correct me if I'm wrong..

Cheers Jim, nice to know I wasn't a million miles away even if the details were blurred in my brain!

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how about a modern computer?

I'd like to see a comparison of how long a typical PC (or even a phone) would take to break the code using the same inputs

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Re: how about a modern computer?

Brute forcing with a current PC would still have been useless in the war as the key-space is too big and they were changed daily. There is (was?) a distributed processing outfit that were trying to crack some last remaining texts, but the site doesn't seem to have been updated in a while, even though one such text was still uncracked.

The Bletchley Park crowd used extra information gleaned from sloppy procedures from the Germans - one instance I've heard of is that there was a weather service Enigma broadcast that got reused for something, or particular operators would always begin a message the same way, or other such tweaks that can help get a hint as to the rotor settings (or narrow down the solution space) and it was these that were fed into the bombe.

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Re: how about a modern computer?

+lots of upvotes for visiting - it's about 5 years since I went, but it was fascinating even then. Particularly amazing to find that the reason it wasn't open to the public or widely known about in my youth was that the place, and the work it did, remained secret until ridiculously recently, the 70s I think.

Re comparison with modern computers - I don't know about the Bombe, but the boffins (proper ones, brown overalls and everything) demonstrating the rebuilt Colossus told me that it did its stuff at a rate comparable with a 286 PC running about about 12MHz. Of course it had a comparatively tiny "instruction set" - it ran stored programs but was closer to a dedicated hardware device than a general-purpose computer (so more like the ALU or GPU than the CPU in a modern machine) - but still mightily impressive. (OK, I understand that anyone too young to remember the 286 won't be that impressed, but that's just the ignorance of youth.)

Equally amazing was its paper-tape reader, a fantastic Heath-Robinson contraption nearly as tall as me, which apparently managed a read speed of 5Kb/s whilst almost having your eye out.

Unmissable stuff.

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If you have any interest at all in the subject...

...get up to Bletchley Park for the day. Seriously, and make sure you take one of the tours (especially if the older fellow who actually worked there during the war is still there). It was quite possibly the best day trip I've ever made. Plus they've got the National Museum of Computing up there too, so you can coo over all the old hard drive platters which come up to your waist - not to mention the Colossus rebuild, of course...

And as FartingHippo mentioned up there, that was the hardest part for me to get my head around - the fact that we could pretty much decrypt all the enemy's transmissions but still had to make the enemy think that their systems were secure. Put yourself in that situation: you know the enemy is going to attack your forces, or even your civilians, but any action you take might mean that you can never again intercept any enemy communications.

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Happy

Re: If you have any interest at all in the subject...

Agreed about the visit, I'd upvote you more than once if I could :)

> decrypt all the enemy's transmissions but still had to make the enemy think that their systems were secure.

One of the anecdotes I was told when I was there was that the folks at Bletchley noticed that one German station in in Africa was sending a very short message at the same time every day. Someone guessed that it was the equivalent of "All quiet, nothing to report" and that indeed turned out to be the case.

Of course, it was sent using the new key each day, so as long as it remained the same they had the clue they needed to break each day's key. The word was sent to Allied forces in the area to stay well away from that German position, and a couple of guys had a very quiet war, always "All quiet, nothing to report".

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Re: If you have any interest at all in the subject...

I really hope that story is true, it has brightened my day no end.

Soldier 1: "I dunno what the Fuhrer is on about, this war stuff is easy, we never see any enemies".

Soldier 2: "Probably running scared from us!"

Soldier 1: "Yeah that's it! Haha".

Solder 2: "Ah well, guess it is time to send in today's report"

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Boffin

Re: If you have any interest at all in the subject...

The crib equivalent to successfully guessed plaintext, e.g. "All quiet, nothing to report" or preferably something a bit longer - obviously in German with spaces removed and using military acronyms - would have massively reduced the number of keys needing to be searched based on the rule that a letter never encrypted as itself, which would have excluded most of the remaining keyspace to be searched.

They alligned the guessed plaintext against the typically longer ciphertext message until no letters corresponded between the 2. A crib longer than 50 characters or so would give a higher probability of a match (based on no matching letters) not occurring by accident. If the crib was long enough and guessed correctly, this match gave the initial settings for the keysearch, based on the correspondence between plaintext and ciphertext letters in the matching section.

I wonder how this aspect of the Enigma crack can be simulated in the modern cryptanalysis challenge based on use of the same cipher ? For this to work, the cryptanalysts need to know part of the plaintext.

I couldn't agree more about Bletchley Park being an excellent daytrip.

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Re: If you have any interest at all in the subject...

> I really hope that story is true, it has brightened my day no end.

I have read it - or something very similar - in other places, so you can sure that something like it IS true. The weakest link in the best crypto system is usually the human operator and their sloppy procedures.

"Heil Hitler" was another text string always worth searching for.

But Bletchley Park also acted proactively. They would get the RAF to drop some mines at a certain location in the sea, and would then start looking for German reports which included the word "minen" and/or the details of the location. This was called "gardening".

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Re: If you have any interest at all in the subject...

I read that other cribs came from an operator who repeatedly sent his girlfriend's name as a test, and, of course, the nutters who always began or ended their messages "Heil Hitler".

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Anonymous Coward

Re: If you have any interest at all in the subject...

'clop'

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Re: If you have any interest at all in the subject...

Well worth the trip. And send 'em some money as well.

Regarding the Bombes -- they used wire brush contacts, similar (if not identical) to those used in tab card machines. Don't underestimate the amount of maintenance required to keep one of those electro-mechanical beasts doing its job. When I worked with punched-card machines, one of the skills you needed to know was how to replace brushes and plugboard contacts (and to know which relay, when removed, doubled the speed of the machine -- in direct violation of your lease agreement!).

//Mum was in "the business" at Nebraska Av during the war

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CWMTWRCH

I wonder if I could confuse would be code breakers by using Welsh (encrypted that is, although places like the above look like crypto to the uninitiated eye).

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Happy

Re: CWMTWRCH

encrypting Welsh would look like plaintext.

Wouldn't there be frequency spikes for the letters L, W and N?

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Re: CWMTWRCH

You can find anything on the Internet:

http://www.sttmedia.com/characterfrequency-welsh

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Anonymous Coward

Re: CWMTWRCH

Do I presume that CMWTWRCH is not pronounced "kwimtwitch"?

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Re: CWMTWRCH

"using Welsh"

IIRC, didn't the US use one of the native american languages along with a cadre of native speakers to encrypt/decrypt secret communications?

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Re: CWMTWRCH

Yep, Navaho "wind-talkers"

There was even a movie about that

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