Kryha

File:Kryha-1.jpg

The standard Kryha machine weighed around five kilograms and was totally mechanical. While the machine achieved a measure of popularity, its security was relatively weak; US cryptanalyst William Friedman reported that he solved the device within 2 hours and 41 minutes.

In the history of cryptography, the Kryha machine was a device for encryption and decryption, appearing in the early 1920s and used until the 1950s. The machine was the invention of Template:Ill (born 31.10.1891 in Charkow, Russian Empire, committed suicide in Baden-Baden in 1955).<ref name=cryptologia-alexander-von-kryha>Template:Cite journal</ref> During the Second World War, Kryha worked as an officer for the German Wehrmacht.<ref name=cryptologia-alexander-von-kryha/> There were several versions; the standard Kryha machine weighed around five kilograms, and was totally mechanical. A scaled down pocket version was introduced later on, termed the "Lilliput" model.<ref name=cryptologia-kryha-lilliput>Template:Cite journal</ref> There was also a more bulky electrical version.<ref name=cryptologia-operational-use-and-cryptanalysis-of-the-kryha/>

The machine was used for a time by the German Diplomatic Corps, and was adopted by Marconi in England.<ref name=cryptologia-operational-use-and-cryptanalysis-of-the-kryha/>

Operation

File:Kryha-2.jpg

The inner ring stepped an irregular number of places with each lever press, changing the encryption in a complex manner.

The machine consisted of two concentric rings each containing an alphabet.<ref name=cryptologia-operational-use-and-cryptanalysis-of-the-kryha>Template:Cite journal</ref> The inner alphabet was stepped a variable number of places by pushing a lever. In operation, the user would encrypt by finding the plaintext letter on one ring (usually the outer ring), and reading the corresponding letter on the other ring; this was then used as the ciphertext letter.<ref name=cryptologia-operational-use-and-cryptanalysis-of-the-kryha/> When the lever was pressed, the inner ring would step, causing the relationship between the two alphabets to change. The stepping was irregular and governed by the use of a disk with a number of sectors, each containing a number of teeth.<ref name=cryptologia-operational-use-and-cryptanalysis-of-the-kryha/>

Cryptanalysis

File:Kryha-patent.png

The Kryha machine was patented in the US in 1930; the design shows two concentric discs labelled with the alphabet.

The security of the machine was evaluated by the mathematician Georg Hamel, who calculated the size of the key space.<ref name=cryptologia-kryha-lilliput/> The US Army was also contacted to see if they would be interested in using the machine, and were persuaded to accept a challenge message to evaluate the security of the device. The challenge message, 1135 characters long, was solved by William Friedman, assisted by Solomon Kullback, Frank Rowlett and Abraham Sinkov, in 2 hours and 41 minutes.<ref name=cryptologia-alexander-von-kryha/>

References

• Alexander von Kryha, "Coding machine", {{#if:1744347

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• Alan G. Konheim, Cryptanalysis of a Kryha Machine, EUROCRYPT 1982, pp49–64.
• Cipher A. Deavours and Louis Kruh, "Machine Cryptography and Modern Cryptanalysis", Artech House, 1985, chapter IV.

External links

• Template:Commons category-inline
• Jerry Proc's pages on the Kryha: Standard, Electrical and Lilliput.
• Standard Kryha: Machine cover open and Machine cover closed
• Nick Gessler's page on the Kryha: Photographs