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ColossusThe secrets of Bletchley Park's code-breaking computers$
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B. Jack Copeland

Print publication date: 2006

Print ISBN-13: 9780192840554

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780192840554.001.0001

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PRINTED FROM OXFORD SCHOLARSHIP ONLINE (oxford.universitypressscholarship.com). (c) Copyright Oxford University Press, 2021. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in OSO for personal use. date: 16 June 2021

Bletchley Park’s Sturgeon—The Fish That Laid No Eggs

Bletchley Park’s Sturgeon—The Fish That Laid No Eggs

Chapter 25 Bletchley Park’s Sturgeon—The Fish That Laid No Eggs

Frode Weierud

Oxford University Press

This chapter describes the Siemens & Halske T52 cipher machines and explains how Bletchley Park broke them. (See photograph 51.) Many authors have confused the T52 with the Tunny machine, and have erroneously linked the T52 to Colossus. The German armed forces employed three different types of teleprinter cipher machines during the Second World War: the Lorenz SZ40/42a/42b (Tunny), the Siemens & Halske Schlüs-selfernschreibmaschine (SFM—Cipher Teleprinter Machine) T52, and the one-time-tape machine T43, also manufactured by Siemens. The Siemens T52 existed in four functionally distinct models: T52a/b, T52c, T52d, and T52e (there was also the T52ca, a modified version of the T52c). At Bletchley Park all T52 models went under the code name ‘Sturgeon’. The Siemens T43 was probably the unbreakable machine that BP called ‘Thrasher’. (This came into use relatively late in the war, and appears to have been used only on a few selected links.) In 1964 Erik Boheman, the Swedish Under-Secretary of State, first revealed that Sweden had broken the T52 during the Second World War. The Swedish successes against the T52 are the topic of Chapter 26. It was only in 1984 that the British officially acknowledged that Bletchley Park had also enjoyed some success against the T52. Not only did BP intercept traffic enciphered on the T52; it also broke all the different models that it discovered. It was clear from the beginning that the T52 was a very difficult machine to break. Probably it would have remained unbroken had it not been for German security blunders in using the machines. The blame should not be put entirely on the German teleprinter operators, however: the designers of the machines at Siemens, who failed to listen to the advice of the German cryptographic experts, were also responsible. The Siemens engineers seem to have focused more on the engineering problems than on the cryptographic security of the machine. The T52a/b and the original T52c were machines with quite limited security. The T52c is an extraordinary example of how not to go about designing a cryptographic machine. The wheel-combining logic, which was meant to strengthen the machine, had exactly the opposite effect—it eased the task of breaking the machine.

Keywords:   Bombe, Geheimschreiber, Hagelin cipher machine, Q-code, Russian front, Sturgeon, TAPIR, Thrasher, autoclave

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