The Condenser PBJ cipher machine
Eugen Antal, Paul Reuvers, Pavol Zajac · Cryptologia · 2024
Condenser PBJ is a mechanical cipher machine developed by Pavel Baráček-Jacquier (1885-1969). It was created between 1922 and 1924, and was used by the Czechoslovak diplomatic service until 1934. The machine was designed to be used as a tool for condensing telegraphic messages in a similar way to a codebook, but with encryption added to the result. The encryption algorithm is a polyalphabetic substitution cipher—an autokey cipher with a priming key of length 10. This autokey cipher is different however from the classical Vigenère autokey cipher. We have been able to fully reconstruct the encryption algorithm. We also present a detailed description of the machine, and point out some weaknesses in the cipher’s design.