German 5-figure Diplomatic Code - "Satzbuch Drei"

This is a scan of two worksheet pages of a German diplomatic code, called Satzbuch Drei ("Codebook Three") by the Germans. Judging from the number of worksheets with additional pages of the code, found in the FRA archives, I'd say this code was pretty well broken. As can be seen, this is an ordered code, and hence it was used with superencipherment for added security. The Germans used two systems to superencipher their diplomatic codes. One, the Blockverfahren ("Block method") used one-time pads (OTP) and were thought immune to cryptanalysis, but the other called Grundverfahren ("Basic method") reused the key, and thus permitted cryptanalysis.

Allied cryptanalysts broke both the Grundverfahren - called "Floradora" by the British and "GEC" by the Americans - and the Blockverfahren - called "GEE" by the Americans. It turned out, the OTP's wasn't truly random, but produced by a special machine which could be reconstructed.

The interested reader is further referred to the excellent article on German diplomatic cryptosystems found in the April 1998 issue of Cryptologia, by Michael van der Meulen.

This is a sample of a telegram enciphered with this code and the Grundverfahren / Floradora / GEC method. The letter group egunlura is an indicator, giving the starting points - the code groups were superenciphered twice, starting at two different locations in the key - in the key pad for the Grundverfahren method. Unfortunately, no key was found in the archives, so the meaning of the telegram still remains a secret.

Back to index page