Editing SIGABA (section)

==History==
[[File:M-134 cipher machine.png|thumb|M-134 Converter, without paper tape reader]]
[[File:Key tape for the M-134 cipher machine.png|thumb|Key tape for the M-134]]
It was clear to US cryptographers well before World War II that the single-stepping mechanical motion of rotor machines (e.g. the [[Hebern rotor machine|Hebern machine]]) could be exploited by attackers. In the case of the famous [[Enigma machine]], these attacks were supposed to be upset by moving the rotors to random locations at the start of each new message. This, however, proved not to be secure enough, and German Enigma messages were frequently broken by [[Cryptanalysis of the Enigma|cryptanalysis]] during World War II.

[[William Friedman]], director of the [[United States Army|US Army]]'s [[Signals Intelligence Service]], devised a system to correct for this attack by truly randomizing the motion of the rotors. His modification consisted of a [[paper tape]] reader from a [[Teleprinter|teletype]] machine attached to a small device with metal "feelers" positioned to pass electricity through the holes. When a letter was pressed on the keyboard the signal would be sent through the rotors as it was in the Enigma, producing an encrypted version. In addition, the current would also flow through the paper tape attachment, and any holes in the tape at its current location would cause the corresponding rotor to turn, and then advance the paper tape one position. In comparison, the Enigma rotated its rotors one position with each key press, a much less random movement.  The resulting design went into limited production as the '''M-134 Converter''', and its message settings included the position of the tape and the settings of a plugboard that indicated which line of holes on the tape controlled which rotors. However, there were problems using fragile paper tapes under field conditions.

Friedman's associate, [[Frank Rowlett]], then came up with a different way to advance the rotors, using another set of rotors. In Rowlett's design, each rotor must be constructed such that between one and four output signals were generated, advancing one or more of the rotors (rotors normally have one output for every input). There was little money for encryption development in the US before the war, so Friedman and Rowlett built a series of "add on" devices called the '''SIGGOO''' (or M-229) that were used with the existing M-134s in place of the paper tape reader. These were external boxes containing a three rotor setup in which five of the inputs were live, as if someone had pressed five keys at the same time on an Enigma, and the outputs were "gathered up" into five groups as well — that is all the letters from A to E would be wired together for instance. That way the five signals on the input side would be randomized through the rotors, and come out the far side with power in one of five lines. Now the movement of the rotors could be controlled with a day code, and the paper tape was eliminated. They referred to the combination of machines as the M-134-C.

In 1935 they showed their work to [[Joseph Wenger]], a cryptographer in the [[OP-20-G]] section of the [[United States Navy|U.S. Navy]]. He found little interest for it in the Navy until early 1937, when he showed it to Commander [[Laurance Safford]], Friedman's counterpart in the [[Office of Naval Intelligence]]. He immediately saw the potential of the machine, and he and Commander Seiler then added a number of features to make the machine easier to build, resulting in the '''Electric Code Machine Mark II''' (or ''ECM Mark II''), which the navy then produced as the CSP-889 (or 888).

[[Image:SIGABA-patent.png|right|320px|thumbnail|SIGABA is described in {{US patent|6175625}}, filed in 1944 but not issued until 2001.]]
Oddly, the Army was unaware of either the changes or the mass production of the system, but were "let in" on the secret in early 1940. In 1941 the Army and Navy joined in a joint cryptographic system, based on the machine. The Army then started using it as the '''SIGABA'''. Just over 10,000 machines were built.<ref name="Fagone2017">{{cite book|author=Jason Fagone| title=The Woman Who Smashed Codes: A True Story of Love, Spies, and the Unlikely Heroine Who Outwitted America's Enemies|url=https://books.google.com/books?id=V00ODQAAQBAJ|date=26 September 2017| publisher=HarperCollins|isbn=978-0-06-243050-2}}</ref>{{rp|p. 152}}

On 26 June 1942, the Army and Navy agreed not to allow SIGABA machines to be placed in foreign territory except where armed American personnel were able to protect the machine.<ref name="Sterling">{{cite book| last=Sterling|first=Christopher H|title=Military Communications: From Ancient Times to the 21st Century| year=2008|publisher=ABC-CLIO| location=USA| isbn= 9781851097326| pages=565}}</ref> The SIGABA would be made available to another Allied country only if personnel of that country were denied direct access to the machine or its operation by an American liaison officer who would operate it.<ref name="Sterling" />