Siemens T-52 "STURGEON"


 
 
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This T-52 is on display at the National Cryptologic Museum. It is believed that between 600 and 1,200 of these machines were manufactured. Their physical weight and the sensitive traffic they handled restricted their wide deployment. The German Air Force began using the Siemens T-52 in 1942.  (Photo by Jerry Proc) 
GENERAL

The Siemens & Halske T52, also known as the Geheimschreiber (secret teleprinter) was an on-line cyphering machine .  British cryptanalysts code named the machine and its traffic by the name  "Sturgeon". Because messages were sent over landlines, the British had little access to Sturgeon traffic. However, some models of Sturgeon were later adapted for point to point radio transmissions.

While the Enigma machine was generally used by field units, the T52 was an online machine used by Luftwaffe and German Navy units, which could support the heavy machine, teletypewriter and attendant fixed circuits. It fulfilled a similar role to the Lorenz SZ 40/42 machine in the German Army.

Ten wired rotors created the encryption maze. That permitted 893 quadrillion (893 followed by 15 zeros) possible combinations on one wheel order.  The key list indicated five of the positions to use. Next the operator selected the other five settings and sent them in the clear to the receiving end.

The British cryptanalysts of Bletchley Park code named the German teleprinter ciphers Fish, with individual cipher-systems being given further codenames. Just as the T52 was called Sturgeon, the Lorenz machine was codenamed Tunny.

Although a British cryptanalytic attack made considerable progress, the results were far slimmer than against the Enigma, both because the difficulty of attack yielded fewer breaks, and because there was a lot less traffic sent over these systems.

OPERATION

The teleprinters of the day emitted each character as five parallel bits on five lines, typically encoded in the Baudot code or something similar. The T52 had ten pinwheels, which were stepped in a complex nonlinear way, based in later models on their positions from various delays in the past, but in such a way that they could never stall. Each of the five plaintext bits was then XORed with the XOR sum of 3 taps from the pinwheels, and then cyclically adjacent pairs of plaintext bits were swapped or not, according to XOR sums of three (different) output bits. The numbers of pins on all the wheels were coprime, and the triplets of bits that controlled each XOR or swap were selectable through a plugboard.

This produced a much more complex cipher than the Lorenz machine, and also means that the T52 is not just a pseudorandom number generator-and-XOR cipher. For example, if a cipher clerk erred and sent two different messages using exactly the same settings a depth of two in Bletchley jargon this could be detected statistically but was not immediately and trivially solvable as it would be with the Lorenz.

MODELS

There were several (mostly incompatible) versions of the T52: the T52A and T52B (which differed only in their electrical noise suppression), T52C, T52D and T52E. While the T52A/B and T52C were cryptologically weak, the last two were more advanced devices -  the movement of the wheels was intermittent, the decision on whether or not to advance them being controlled by logic circuits which took as input data from the wheels themselves.

In addition, a number of conceptual flaws (including very subtle ones) had been eliminated. One such flaw was the ability to reset the keystream to a fixed point, which led to key reuse by undisciplined machine operators.

For additional reading:

* John Savard's excellent web article on the mahine
* The Rutherford Journal article -  please select this link.



 
 
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A Geheimschreiber 52 made by Siemens & Halske in 1941 (Serial no: 34387) shown with the cover removed. It is sitting atop its original shipping box. This example is held by the Norwegian Armed Forces Museum in Oslo, Norway. (Photo courtesy of Reidar Olsen, Norway. E-mail:  trolok45@c2i.net)

 
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Above and below: Another pristine example of the T-52 made by Siemens & Halkse. This machine was for sale as of January 2002 and the asking price was $US 85,000 plus shipping.  (Photo and copy courtesy John Alexander, G7GCK )

 
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With the cover off. 


Contributors and Credits:

1) John Alexander, G7GCK Leicester, England.
2) http://en.wikipedia.org/wiki/Siemens_and_Halske_T52
3) Die Welt der geheimen Zeichen by Klaus Schmeh
4) The Rutherford Journal     http://www.rutherfordjournal.org/article010106.html
5) John Savard http://www.quadibloc.com/crypto/te0302.htm
6) Sturgeon placard at NCM.
7) Reidar Olsen, Norway.  <trolok45(at)c2i.net>

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Apr 26/12