The Kryha cryptograph had a number of variations. It had two disks, each with a scrambled alphabet that could be changed by the user. One disk moved for each letter enciphered. The movement was controlled by a pinwheel; if there were, on the pinwheel at one place, five teeth out followed by one pushed in, then that caused the moving disk to move five places forwards for one letter.
An earlier model used a fixed gear, which caused the following movements, in order:
7 6 7 5 6 7 6 8 6 10 5 6 5 7 6 5 9
Essentially, the cipher it produced was similar to a progressive-key encipherment with a keyword and mixed alphabets. Although it took W. F. Friedman only a few hours to solve a message enciphered on one of these machines, the principles required are already beyond those normally dealt with in books on cryptanalysis aimed at amateurs and beginners.
Although the version of the machine solved by W. F. Friedman in "2 Hours, 41 Minutes" (the title of the chapter in Machine Cryptography and Modern Cryptanalysis by C. Deavours and L. Kruh discussing the Kryha machine) appears to have been the fixed-gear version, since Friedman was not given the machine to examine, he did not have the opportunity to solve its cipher even more quickly, as in that case, only 17 trials would have been needed to sort the letters of the test message into monalphabetically-enciphered groups.
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