The official name for the machine is Schlüssel-Fernschreibmaschine
SFM T-43. It is based on the earlier
T-37 teleprinter, and has a paper-tape
reader/puncher to the left of the keyboard.
For each character typed on the keyboard, a random character is read from
the key tape and mixed with the original character by means of an
XOR-operation. Once the key character is read from the
paper tape, it is destroyed by the built-in puncher, so that it can not be used
Images of the T-43 are extremely rare and they all seem to originate from the
same -single- source. The image on the right is currently the best one
we have been able to locate.
The T-43 was codenamed Sägefisch (Sawfish) by the Germans,
because of the typical sound of its modulated signal.
The codebreakers at Bletchley Park called it
'Trasher'. It is currently unknown how the key tapes were produced and
distributed, but according to eye witness Georg Glünder,
the designers said that the tapes were created by Random Number Generators
(RNG) and that they did not have a cryptographic period .
This is contradicted by Michael Pröse however .
The principle of the T-43 mixer machine is based on the so-called
Vernam Cipher invented by Gilbert Vernam in the US
in 1917. Gilbert Vernam was also the inventor of the stream cipher and
the co-inventor of the One-Time Pad (OTP). According
the NSA, it is probably one of the most important inventions in the
history of cryptography. Nevertheless the Germans were
probably the first
to develop a practical implementation of it for the encryption of telegraph signals: the T-43.
The T-43 entered service relatively late in the war and only a modest number
of machines was built. It is believed that between 30 and 50 machines were
At the end of the war, some T-43s were found and confiscated by the Allies.
It is known that the American TICOM-commission shipped six T-43 machines
to the US and an equal number of German crypto-experts.
The machines that were captured in Norway, were shipped to
Bletchley Park (UK)
It will come as no surprise that the T-43 was kept secret by the Allies
for many years. Strangely enough though, the history of the machine is
still a mystery today.
At the time or writing (2013) no surviving machines are known to the public and
further information from British and American archives has not yet been
Shortly after WWII, the US, and later also the new Allied organisation
started using ETCRRM mixer machines
that were based on the T-43 principle.
These machines were made by the Norwegian manufacturer
STK and sold to the US and to NATO.
➤ Who was first?
If the key tapes for the T-43 consisted of a truly
random sequence of characters, the machine would theoretically have been
unbreakable. According to Michael Pröse however,
the sequence was pseudo-random, as it was generated by two cascaded
Siemens T-52e machines .
Another weakness was caused by TEMPEST problems.
The mechanical delay of the internal cipher relay caused
a phase-shift between the clear text and the cipher text,
which was visible on an oscilloscope.
This unwanted side-effect was discovered by the German crypto-experts of
As it allowed the clear text to be reconstructed from the transmitted
signal, extra filters were later added to the existing T-43 machines.
Meanwhile, Siemens developed an improved machine with a different
construction that would not exhibit the
TEMPEST problem, but the war
had ended before that machine could be taken into production.
It is currently unknown whether or not the above weaknesses were exploited by
but no evidence for this has been found so far.
Cryptanalysts at BP
initially thought that the key tapes were produced
by a Lorenz SZ-42 as they found regularities
in the key sequence. This is probably the reason why the codebreakers
chose a fish-name for this machine (Trasher).
It also supports Michael Pröse's claim that the key tape was generated with
two T-52e machines
Over the years, many have claimed to have invented the principle of
the mixer machine. In the late 1950s, the Dutch PTT filed a design for
such a machine that later became known as the
Ecolex cipher machine. Although a patent
was granted, they were by no means the first ones to have 'invented' it.
Several years earlier, in 1952, a similar patent was filed by Bjørn
Røhrholdt and Kåre Meisingset of STK
in Norway. That machine became known as the
ETCRRM and was soon one of the favorites
of the Americans. It was later used on the
These patents can be declared invalid however, as Siemens developed
the T-43 in 1943, based on the prior art of the Siemens patent filed in 1921.
The image above shows part of a drawing in
German Patent DE371087
in which the two tape readers are clearly visible side-by-side .
The Siemens patent would probably not have survived a potential
lawsuit though, as it was the American Gilbert Vernam
who filed his design for the same concept first, on 13 September 1918 .
Although his drawings are not identical to the drawing in the German patent,
there are some remarkable similarities. In their patent, Siemens recognizes
earlier developments in this field and adds online use to it.
The T-43 was probably the first machine to use it for online encryption.
Although Gilbert Vernam's
invention dates back to 1918, in his paper of 1926  he describes
the keystream as a mixture of two looped punched-paper tapes of a
different length. This means that the cipher period is finite.
The Telekrypton machine
of 1933 was based on this principle.
In 1942, at the request of British Intelligence, Canadian communications
expert Benjamin deForest Bayly converted the
American Telekrypton into
a real One-Time Tape (OTT)
cipher machine. The machine is ready in 1943
and becomes known as Rockex.
Around the same time, another machine, known as the
enters service in the UK. For the remainder of the war it is used for
the distribution of Ultra Intelligence.
As all three systems were introduced around the same time,
it seems fair to recognise the T-43,
and 5-UCO, all
as the first mixers.
Please note that this page is still under construction and that it currently
only acts as a placeholder for information about the Siemens T-43.
If you have any information about this machine that you are able share,
please contact us.
- Georg Glünder, Als Funker und 'Geheimschreiber' im Krieg 1941-1945
München (Germany). PIONIER 11/12-1989, 1/2-1990. First publication.
Reproduction 27 March 1990. Later reproduced in .
- Georg Glünder, Als Funker un 'Geheimschreiber' im Krieg 1941-1945
The Enigma Bulletin. No. 1, December 1990. German.
- Klaus Schmeh, Hitlers letzte Maschinen
Hitler's last machines (German).
2 August 2004. Retrieved May 2012.
- Michael Pröse, Chiffriermaschinen und Entzifferungsgeräte im Zweiten Weltkrieg:
Technikgeschichte und informatikhistorische Aspekte.
Dissertation, Leipzig, December 2004. German.
- German Patent DE371087
Patent describing the principle of a mixer machines.
Filed: 10 July 1921.
- Gilbert Vernam, US Patent US1310719
First patent describing a machine for 'mixing' telegraph signals.
Filed: 13 September 1918.
- G.S. Vernam, Cipher Printing Telegraph Systems
AIEE (IEEE) VOL. XI.V. pp. 109-115. February 1926 1
The American Institute of Electrical Engineers (AIEE) was merged
with the Institute of Electrical and Electronics Engineers (IEEE)
on 1 January 1963 and is now known as IEEE. The document cited here
is located off-site and is reproduced there by permission of the IEEE
(read the enclosed copyright notice).
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© Crypto Museum. Created: Wednesday 15 February 2012. Last changed: Friday, 13 September 2019 - 05:59 CET.