Kryha

The Kryha is one of Alexander von Kryha (1891-1955) developed in the 1920s, mechanical cipher machine with a fixed periodic key.

Kryhas idea was to automate the rotation of a cipher with the help of a spring drive. In 1923, the unit came as Kryha cipher machine on the market.

Cryptanalysis

The safety of the machine was checked by the mathematician Georg Hamel, who calculated the size of the key space.

In 1933, William F. Friedman could read together with Solomon Kullback, Frank Rowlett, and Abraham Sinkov an encrypted message with Kryha consisting of 1135 characters within two hours and 41 minutes. In spite of the demonstrated weakness of the machine, it was not until the 1950s used.