The Kryha Cipher Machine

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[click on a thumbnail to expand the image]

The Kryha machine is named after its inventor, Alexander von Kryha, whose career is described in:

Schmeh, K. 2010. “Alexander von Kryha and his Encryption Machines.” Cryptologia 34(4): 291‐300.

Descriptions of the machine and methods of attacking it can be found in:

Deavours, C. A. and Kruh, L. 1985. Machine Cryptography and Modern Cryptanalysis. Artech House, Norwood, Massachusetts. ISBN 0-89006-161-0. See Chapter IV, “2 Hours, 41 Minutes.”

Marks, P. 2011. Operational Use and Cryptanalysis of the Kryha Cipher Machine. Cryptologia 35(2): 114‐155.

Callimahos, L. 1973. Q.E.D. – 2 Hours, 41 Minutes. NSA Technical Journal, Fall 1973, Vol. XVIII, No. 4. This article is available here.

Konheim, A. G. “Cryptanalysis of a Kryha Machine.” Proceedings of Eurocrypt 82, reprinted in Lecture Notes in Computer Science #149, Cryptography, Proceedings of the Workshop on Cryptography, Burg Feurstein, Germany, March 29 – April 2, 1982, edited by Thomas Beth. Springer-Verlag, Berlin, Heidelberg, New York, 1983. ISBN 0-387-11993-0.

The basic cryptographic principle of the machine is to slide two mixed alphabets against each other in a series of pseudo-random steps. The alphabets are carried on concentric rings (visible in the photographs above) - usually alphabet the inner ring was considered to carry the cipher alphabet and the outer one the plain alphabet. The letters are attached to the rings by spring clips, allowing them to be interchanged as needed. The operator enciphers a letter by simply reading across from the outer to the inner ring and writing down the result. The machine is stepped, either before or after encipherment, by pressing a button protruding from the front of the machine; this causes the inner ring to move through some number of positions in an anticlockwise direction. The stepping is regulated by a control wheel – a gear wheel divided into a number of segments having varying numbers of gear teeth – that moves from one segment to the next each time the button is pressed, driving the inner ring via a gear train.

The machine was evaluated and rejected early in 1930 by the U.S. Army's Col. Parker Hitt.  Manuscripts of two documents describing his solution have survived; transcripts of these are available here and here.

Various businesses and government agencies used the machine, especially in Germany. Kryha traffic was solved by both British and American cryptanalytic organizations in the World War II era, and various documents describing their work can be found at the US National Archives in College Park, MD, in Record Groups 38 and 457. A transcript of a handwritten document describing solution of traffic related to German wartime trade with Spain (RG457, Historic Cryptographic Collection, NR2417) is available here.

Numerous patent filings cover various models of the machine.

Photographs © Philip Marks 2010