Schneier on Security

Clive Robinson • June 30, 2017 8:59 AM

@ Will,

What held Dilly up was not knowing the order of the keyboard to rotors.

The Poles simply “Guessed at the German regimented mentality” and tried the simple A=1, B=2, … and got it right first go.

As for the early enigma, it got broken fairly easily because it stepped the rotors from the wrong end. Although the British did have an attack method the French actually imoroved on it (see rod and cliques methods). And for all it’s mechanics the enigma can still be tested or emulated by simple strips of paper three for the rotors and one for the stecker board.

Importantly the real secrets behind much of the breaking was the “Dockyard cipher” and the weather information and a catalogue combined later with traffic analysis.

The dockyard cipher was weak and the British went over and dropped a few mines etc (gardening) outside a German controled harbour knowing that a standard message would be sent out on both the dockyard cipher and the more secure kriegsmarine systems, thus a known plaintext could be obtained from the dockyard system to be used to attack the kriegsmarine system. Similar was done with weather messages and joint operations with the Italian’s who’s systems were weak.

But in the main the main way the enigma got broken was via probable plaintexts. The German’s had a very regimented way of sending signals often starting with a well known name etc which was “circuit based” and they also tended to end with Heil Hitler”. Huf Duf (HF DF) and later Traffic analysis gave the circuit or net information, which could be used to get names and other information from the catalogue of over 2million pieces of information kept on library “file cards” which gave probable plaintexts by which crib settings were obtained.

With out the catalogue which was started before day one of enigma breaking the majority of breaks would not have been possible.

There were also other weaknesses in the German keying systems that gave rise to the likes of “cillies” etc. Basically humans are both lazy and non random. It was observed that a key for a new message often was just a couple of rotor movments away from the last positions from the previous message sent/received. Further at turn around at midnight when the enigmas were reset up, if there was a rotor change, then the chances were the operator would have the ring setting values uppermost in the enigma and thus the first message sent would have keying informatio close to the ring setings more often than not.

But to make a point, it took Alan Turing several months to come up with the bomb idea. Gordon Welchman however did it independently from scratch in a few days. Further Gordon went on to design the all important diagonal board that when he described it left Alan and several others entirely speachless. Gordon also put in place the idea of Traffic Analysis and it later became the cause of his name becoming blackened by the UK Gov in the 1980’s when Maggie Thatcher went on the war path against “leakers”. Gordon wrote a book about his experiences in which he described the mechanics of Traffic Analysis. It turns out that although upset over Winterbotom’s revelations in the early 1970’s which caused some nations to stop using their old enigmas and similar US war surplus ciphers, the secret the British wanted kept hidden was Traffic Analysis.

Thus nolonger being a British Citizen Gordon wrote his book unaware of a couple of things, a secret agreement that was a follow on from the BRUSA agreement, that what the British decided was classified the NSA et al would respect as classified and the sensitivity over Traffic Analysis.

The result was he had his US security clearence revoked and the US IC then tried various tricks to bankrupt him…

It’s a shame because other work that Gordon did was the fundemental work that gave us the Internet through Rand where he worked the DOD DARPA and Bolt, Beranek and Newman (BBN) in Cambridge, just up the Charels river from Boston, and MIT where the two B’s were profs.

The US developement of bombs was a little unusual, theor design was based around relays, that although faster than the origanal British Turing bomb was nowhere near as fast as the later supper bombs required to break the four wheel enigma with a choice of eight rotors the Getman submarine enigmas became. Further late in the war was the Luftwaffe fourty position “Uhr box” which if it had been brought into service much earlier and in a more general way would probably have defeated the alied breaking of enigma entirely.

The whole history of the enigma was one of “riding the leading edge” the Germans were over confident in the system they had put together, and only slowly made incremental improvements. This alowed the Brirish to come up with improvments in their methods “only just in time” and aby one of them happening six months prior to the actual date it was introduced would have either killed or very servearly set back the ability to break the enigma as regularly as it was.