[cctalk] Re: auction starting in 50 minutes

On 9/10/24 17:37, Maciej W. Rozycki via cctalk wrote: The army version only had 3 rotors because the Germans figured army messages would be useful only for a short time (move to next bridge over river) and useless after an hour or so.  the Germans knew that the Enigma was a weak system, so they figured they needed better for the navy (meet sub tender at 9AM at coordinates XY) as the messages could be of use by the time they were broken. The Germans apparently had no idea that the allies put together a MASSIVE mechanized code breaking effort.  Bletchley Park had 6 bombes of the Turing design, but the US had 360 machines made by NCR under insane secrecy.  If you saw the movie "The Imitation Game" the model they showed was pretty accurate.  It tried about 24 combinations per second, and took quite a while to find the starting position for the navy code.  The NCR machines ran so fast that when they got a match they had to brake to a stop and back up to record the match.  The British bombe rang a bell and stopped when it got a selected level of a partial match, the NCR machine recorded the match on adding machine tape and then continued trying the rest of the possible combinations.  it tried 1440 combinations/second, and could break the navy code in under 20 minutes, the army code in six minutes. The code was changed every midnight, so for the first message of the day the code breakers had to guess which rotors were to be used that day.  There were 7 rotors, you picked either 3 or 4 for army or navy respectively.  In the US, they set up 26 machines (I think) with all possible combinations of rotors and then found the starting position of the only one that came out right.  Then, once they knew which rotors to use, they re-set all 360 machines to that arrangement and cracked the starting position of 360 messages in parallel.  The messages were sent by underwater cable to the US for cracking from various intercept sites. For higher level message traffic, the Germans had the Lorenz SZ42 (Schlussel Zusatz, literally key attachment, but meaning cypher attachment) which was a VERY strong (for the time) modern encryption device.  But, it too, had a weakness.  The Bletchely Park guys had intercepts of this system that they codenamed "Tunny" and the sender and recipient were indicated in clear text, so they knew this was important stuff.  The machine had rotors that had different numbers of steps, related by prime numbers, so that the cryptoperiod was quite long.  One rotor of each group could either XOR one serial data bit of the Teletype character, or not alter it.  There were two groups of 5 rotors.  Each rotor had "bumps" that could be flipped up or down.  One group of rotors advanced one step for each character, the other group advanced intermittently, determined by two other rotors.  Bletchely Park NEVER saw one of these machines, but by MASSIVE statistical analysis, they managed to figure out completely how it worked, which blows me away!  They built an electronic code cracking machine that ran two paper tapes that differed in length by one character, and as the tapes ran through the reader repeatedly, this managed to compare every character of the ciphertext against every character of the crib tape, and the machine accumulated some statistical information from that.  This machine was called "Colossus". One of the huge cracks they got was a long message from Gen. Erwin Rommel detailing what he thought were the strengths and weaknesses of the allied positions.  We used that to take advantage of what we thought the Germans would do to exploit that. Another big crack was an Irish navy officer had been killed, and with his family's permission, papers with disinformation on the D-day attack were put in his pockets.  Tunny intercepts later showed the Germans were moving positions based on this disinformation, and it helped the invasion go better for the allies. Jon