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Kryha

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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 Alexander von Kryha [de] (born 31.10.1891 in Charkow, Russian Empire, committed suicide in Baden-Baden in 1955).[1] During the Second World War, Kryha worked as an officer for the German Wehrmacht.[1] 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.[2] There was also a more bulky electrical version.[3]

The machine was used for a time by the German Diplomatic Corps, and was adopted by Marconi in England.[3]

Operation

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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.[3] 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.[3] 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.[3]

Cryptanalysis

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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.[2] 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.[1]

References

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  1. ^ a b c Schmeh, Klaus (2010). "Alexander von Kryha and His Encryption Machines". Cryptologia. 34 (4): 291–300. doi:10.1080/01611194.2010.485440.
  2. ^ a b Kruh, Louis (1985). "THE KRYHA LILIPUT CIPHERING MACHINE". Cryptologia. 9 (3): 252-261. doi:10.1080/0161-118591859988.
  3. ^ a b c d e Marks, Philip (2011). "Operational Use and Cryptanalysis of the Kryha Cipher Machine". Cryptologia. 35 (114–155): 114–155. doi:10.1080/01611194.2011.558978.
  • Alexander von Kryha, "Coding machine", U.S. patent 1,744,347
  • 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.
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