Enigma machine Rejewski cataluge and ring settings

Question

I'm trying to simulate Rejewski cyclometer and developed a code that run over all ~100k posibilities and generates for each setting an id that looks like that: 1313_111212_11221010 I run my code with ring setting set to AAA

I've tested it with random machine settings and when the ring setting is not AAA it does not work. The start position key is actulay shifted. If the ring settings is BBB and the start position is DEB -> the line that relates to the id is CDA - shifts one leteer down.

My question is asuuming that in the real world the ring settings was not AAA how did the catluge helped cracking the daily settings?

Answer 1

The catalogue method gave them the difference between the daily key ring and window settings. To recover the actual ring settings, they used the "ANX method" which was a kind of known-initial-plaintext attack.

Rejewski says, in one of the appendices to Enigma: How the German Machine Cipher Was Broken and How It Was Read by the Allies in World War Two by Kozaczuk that about half of all plaintext messages began ANX (that is, the German word for "to" followed by a space character). Once they'd got the plugboard settings and the rotor order and window-ring difference from the catalogue they would set up a replica Enigma machine accordingly and encrypt ANX in every possible window position until they got output matching one of the prefixes of the day's messages. (You had to have ~100 messages to use the catalogue method, so you would get a match fairly quickly, around 350 tries expected). They already knew the true indicator for that ciphertext from decrypting the message indicator, so the difference between that and the setting that gave a match was the ring setting.

I made a couple of videos about using the catalogue that explain all this in more detail and show and example of using a simulated catalogue.