Alexis Køhl: a Danish Inventor of Cryptosystems

A Danish engineer, Alexis Køhl (1846–1920), invented a number of cryptographic systems between 1876 and 1919. Some of these systems were simple, others were more complicated machine systems. Few of Køhls systems were ever used. One system was used to some extent in the Nordic countries, but generally Køhl felt that his ‘‘genius’’ was not properly recognized. There were no sensational cryptographic innovations in his systems, but some of them were quite smartly implemented. His first machine systems made use of some of the earliest mechanical typewriters. All his life Køhl claimed that his systems were unbreakable. He never made the fortune that he thought he deserved. This paper discusses Alexis Køhl’s life, his systems, and describes the known surviving devices. Additional information would be highly appreciated by the author.