Collaboration and Collation: Breaking German diplomatic ciphers in 1942

Abstract

German diplomatic signals enciphered in the Floradora double-additive system were broken at the end of 1942 as a result of Anglo-American collaboration. The American contribution was a novel and ingenious system of machine search for likely additive combinations, which allowed the choice of additives to be revealed. The paper suggests a reconstruction of the machine methodology, which used punched-card sorting and collation.