This talk will describe how a team of Swedish cryptanalysts broke the electromechanical cryptographic teleprinter "Siemens & Halske T52" which was used by the Germans during World War II for "important" traffic. It contained a stream cipher implementation much more sophisticated than the substitution engine of the well-known Enigma. The talk will focus on reconstructing how the Swedes, specifically the key figure of Arne Beurling, could have gotten the ideas for breaking the cipher -- a process about which next to no historical accounts exist.
