Fighting for relevance: Economic intelligence and special operations executive in Spain, 1943–1945

Operational Use and Cryptanalysis of the Kryha Cipher Machine

“…Note that each sequence is delineated by a repeated character; there are no conflicts where the same letter appears in the same place in both sequences (this would be a contradiction, implying both zero and non-zero values for the multiplier m); and there are confirmations within the sequences-L in the first sequence occurs at positions corresponding with A in the second. 33 The practice of double-or multiple-stepping of the machine as a security measure is not mentioned in Kryha's 1925 operating instructions, though an example is given of enciphering differing numbers of spacing characters in between words, and indeed of enciphering a spacer before the first word of a message, but without discussing the improved security that would be obtained by stepping the machine some agreed number of times whenever a word-spacer is encountered. The manufacturer's recommendation of the use of such ''letters of influence'' in their 1951 advertising brochure is mentioned in ([10] p. 162), but in fact the technique is mentioned as early as the marketing materials from 1926 [12].…”

“…The ability to use isomorphisms as an entry point into this traffic was critical, since the correspondents had by then adopted the autokeying practice of double-stepping the machine when enciphering word-spacing characters, rendering infeasible the attacks described so far. 33 …”

“…With its control over payment clearing and with support from the highest levels of the Nazi regime, ROWAK came to exert a near-monopoly over trade between Spain and Germany. Spain's debts to Germany did not end with the civil war, and during the Second World War raw materials from Spain, especially tungsten, were very important to the German war effort and correspondingly to Allied efforts at interdiction [33]. A document by F. W. Lewis dating from about 1942 describes the methods used by Section B-2 of the U.S. Army's Signal Security Agency (a part of the Cryptanalysis branch) to break German Kryha traffic related to the activities of these various companies [32].…”