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Enigma Rotor ← K
The Japanese Enigma
- wanted item
The Enigma T, codenamed Tirpitz, was an
Enigma cipher machine
developed during WWII by the Germans especially for use by the Japanese Army.
It was based on the commercial Enigma K,
but had differently wired wheels (and ETW) and multiple
turnovers on each wheel. Furthermore, it had an Eintrittswalze (ETW)
that was wired differently from all other Enigma machines.
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The machine was intented for communication between the German and
Japanese Navy. The agreement for this was signed on 11 September 1942
by German Vice Admiral Erhard Maertens and Japanese Admiral Tadao Yokoi.
At the time, Maertens was Director of the German Naval Communication Service and
Yokoi was the Japanese Naval Attaché in Berlin. This followed the earlier
Japanese-German Military Agreement of 18 January 1942 [2].
All German-Japanese communication would be encrypted
with a machine that was referred to as T-Enigma
or Enigma Model T.
It was called TIRPITZ by the Germans,
and the Japanese called it TIRUPITSU.
The US Navy referred to the machine as OPAL and the traffic was named
JN-18
[2].
The official name for the machine system was Japanese-German Joint Use
Code No. 3.
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The system consisted of an operational procedure, named TIRPITZ,
and a key list with the name GARTENZAUN (garden fence).
The operational procedures were effective from 1 August 1943 until the end
of the war. In 1999, in an article in Cryptologia, Frode Weierud gave a
detailed account of the TIRPITZ and its historical context. It is available
for download below [2]. Much of the information on this page is based
on that article.
It is not exactly known how many T-Enigmas were actually built.
The Japanese ordered 800 machines, but for various reasons this
amount was never delivered. There were delays in design and manufacture,
and it was increasingly difficult to get sufficient supply of materials.
Furthermore, the Germans started to doubt the security of the
machine. In the meantime, the Japanese used two manual systems:
Sumatra (later Sumatra 2)
and TOGO (later TOGO 2).
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The Enigma T is based on the design of the
Commercial Enigma (K) and not
on the more common Steckered Enigma (I)
that was used by the German Armed Forces.
As the machine was to be used for communication between the Navies of Germany
and Japan, they needed a strong cipher, but didn't want to 'give away'
their crown jewels (i.e. the Service Enigma with Steckerbrett).
Instead they took a standard Enigma K
and improved it in several ways.
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First of all, the entry wheel (ETW) was wired in a random fashion,
different from all other machines. The machine was supplied with 8 coding
wheels (3 in the machine). The most important difference however,
was the presence of 5 turnover notches on each of the 8 wheels.
This caused far more frequent wheel turnovers and extended the cipher
period (as 5 is a relative prime of 26).
In some cases, the operational procedure instructed
the user to advance the settable UKW manually by one position after each
group of 5 letters, adding extra complexity.
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The first order for Enigma T machines was for 400 units, but this order was
never fully delivered. As there were shortages in material, only small batches
of machines were supplied to the Japanese. Some shipments got losts whenever
the carrying U-boat was sunk and one machine was compromised in Guadalcanal
on 15 February 1943. The Germans experimented with the machine and started
doubting its security, especially when using it for a great volume of traffic.
In June 2009 we had a chance to make some close-up photographs of an Enigma-T
wheel. This wheel belongs to the Tirpitz Enigma with serial number T47
that is part of the private collection of the British Intelligence
Service GCQH. More images below.
Shortly afterwards, GCHQ would unexpectedly donate an Enigma-T with
serial number T244 to the
Bletchley Park museum.
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Apparently, the Japanese had acquired the manufacturing rights for the Enigma T,
as on 18 May 1943 they are cancelling that order. Around the same time, the
Germans propose a new machine for joint communication: the 02562-A-Enigma.
According to a report, this is a Steckered machine, most likely based on the
standard Service Enigma. The Germans propose to replace the remainder of the order
(another 400 machines) with this new type.
Part of the initial batch of 400 machines had already been delivered however,
and some machine were under construction. After the Japanese Naval Attaché
expressed his concern about this, the Germans guaranteed that the new machine
would be interoperable with the old one. Using the new machine without plugs
(Steckern) would make the machine compatible with the Enigma T.
If this was the case, the machine would cryptographically be considerably stronger
than the Service Enigma. It would combine the strength of the plug board,
the more frequent turnovers and the increased cipher period. Had it been possible
to deploy this machine widely, it might have defeated the American and British
codebreakers. However, at this point during the war, the material shortages
made it impossible to build large quantities of any machines.
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From then on, small batches of the new machine were delivered to Japan, whilst
the initial order for Enigma T machines was also (partly) fulfilled.
In August 1944, a large batch of Enigma T machines was captured by the Allied
Forces in a warehouse in the vicinity of Lorient. Although there are conflicting
accounts, it is likely that some 70 machines were captured here.
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When Bletchley Park
was first opened as a museum, around 2000, they had an
Enigma on display that could be touched by the public. It was part of the
so-called Crypto Trail that allowed visitors to follow the flow of an
Enigma message. Researchers discovered however, that the machine on public
display was an extremely rare Enigma M3: the standard machine
used by the Kriegsmarine (German Navy), of which only a handful has survived.
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The machine was removed from the hands-on exhibition in 2007 and was locked
away in BP's safe. Since 2011 it is back on public display again, as part of
their Enigma showcase, but this time it is protected by bullet-proof glass.
As they wanted another machine for the hands-on experience, BP director
Simons Greenish asked GCHQ in mid-2007 for a spare Enigma machine of which
they had more than one available. He was assuming to get a standard 3-wheel
Steckered Enigma (Service) machine, but instead, in October 2007 he got a surprise.
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The machine that GCHQ sent to BP was
a non-Steckered machine with 4 adjustable wheels...
After a closer examinition it turned out to be the extremely rare Enigma
T, with serial number T-244. The machine was in pretty bad condition and its
wooden case was missing completely.
Furthermore, there was no serial number plate on the machine's body and
the paint had deteriorated somewhat. Nevertheless it is probably one of the
best unexpected gifts that Bletchley ever received.
The machine has since been restored and is now part of the permanent
Engima showcase in B-Block.
Another Enigma T machine is on display at the NCM.
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The table below shows the wiring of the Enigma T wheels,
the entry disc (Eintrittswalze, ETW) and the
reflector (Umkehrwalze,
UKW) [1]. The rightmost column
shows what letter is visible in the window when the wheel
causes a turnover of the wheel to the left of it.
Please note that these positions are different from the
actual position of the notches on the circumfere of the wheel.
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Wheel
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ABCDEFGHIJKLMNOPQRSTUVWXYZ
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Notch
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Turnover
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#
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ETW 1
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KZROUQHYAIGBLWVSTDXFPNMCJE
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I
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KPTYUELOCVGRFQDANJMBSWHZXI
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EHMSY
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WZEKQ
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5
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II
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UPHZLWEQMTDJXCAKSOIGVBYFNR
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EHNTZ
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WZFLR
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5
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III
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QUDLYRFEKONVZAXWHMGPJBSICT
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EHMSY
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WZEKQ
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5
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IV
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CIWTBKXNRESPFLYDAGVHQUOJZM
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EHNTZ
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WZFLR
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5
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V
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UAXGISNJBVERDYLFZWTPCKOHMQ
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GKNSZ
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YCFKR
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5
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VI
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XFUZGALVHCNYSEWQTDMRBKPIOJ
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FMQUY
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XEIMQ
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5
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VII
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BJVFTXPLNAYOZIKWGDQERUCHSM
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GKNSZ
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YCFKR
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5
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VIII
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YMTPNZHWKODAJXELUQVGCBISFR
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FMQUY
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XEIMQ
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5
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UKW
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GEKPBTAUMOCNILJDXZYFHWVQSR
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Note that this is the only machine with a different wiring for the
ETW. All other Enigma machines have an ETW that is wired either in
the order of the alphabet (ABCDEF...) or the order of the keyboard
(QWERZU...).
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JN-18 traffic (i.e. encrypted on Enigma-T) was not frequently intercepted by the
Americans and was therefore very difficult to break.
At the end of the war, Enigma T was used by the Japanese Naval Attachés and even
for deplomatic traffic after the Japanese destroyed their PURPLE machines.
It is known to have been used between stations in Tokyo, Berlin, Stockholm and Bern.
The exact operating procedure is currently unknown.
In 2009, Frode Weierud published some messages that were believed to have been
enciphered on the Enigma-T [3].
The image above shows a real Japanese Enigma-T message as it was intercepted by
the US Navy's signal intelligence and cryptanalytical group OP-20-G, on 10
March 1944. More sample messages and backgrounds are available from
Frode Weierud's website [3].
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- David Hamer, Geoff Sullivan and Frode Weierud,
Enigma Variations: An Extended Family of Machines
Cryptologia, July 1998, Volume XXII, Number 3, pp. 211-229.
- Frode Weierud, TIRPITZ OPAL
TIRPITZ and the Japanese-German Naval War Communication Agreement.
Cryptologia, July 1999, Volume XX, Number 3, p. 6-10.
- Frode Weierud, German Enigma T (Tirpitz) Messages,
used for Japanese-German Intercommunications.
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© Crypto Museum. Created: Tuesday 11 August 2009. Last changed: Tuesday, 15 September 2020 - 08:57 CET.
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