Floradora

Floradora was a WW2 cipher system used by the Germans for Diplomatic messages. The Germans believed it was impregnable but Allied collaboration between GCCS and SIS broke it.

During WW2 Germany had Embassies overseas in many friendly or neutral countries such as Japan, Eire, Spain, Portugal, Argentina and Mozambique. Diplomatic traffic was essential to communicate strategy and tactics to allied countries. It was also used to gather intelligence such as enemy shipping movements, deployments and reports from agents. 

Such communications were of the highest confidentiality and often lengthy so that a very secure cipher system was needed.

This article, originally written for the American Cryptogram Association, is the story of one such system and how the Allies broke it.