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← Enigma Family tree → Principle →
The rotor-based cipher machines
The history of the Enigma
starts around 1915, with the invention of the
rotor-based cipher machine. As usual in history, the rotor machine was
invented more or less simultaneously in different parts of the world.
In 1917 there were inventions from Edward Hebern in the USA,
Arvid Damm in Sweden, Hugo Koch in The Netherlands
and Arthur Scherbius in Germany [1].
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Invention of the Rotor Machine (1915)
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There is one development however, that pre-dates the others,
and that is the invention
of Theo A van Hengel (1875-1939) and RPC Sprengler (1875-1955), two
Dutch naval officers who produced working rotor-based cipher machines
for the Dutch War Department (Ministerie van Oorlog) in 1915.
This fact was discovered in 2003 and is described in detail in a paper by
Karl de Leeuw [2].
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Officially though, the Enigma machine was invented by Arthur Scherbius
in 1918, right at the end of World War I.
After several years of
improving his invention, the first machine saw
the light of day in 1923.
A year earlier he had secured the rights to
patent NL10700
of Dutch inventor Hugo Koch for a similar device [4].
It was a rather large typewriter-style
machine that was developed by
Scherbius' first company Scherbius & Ritter of Berlin-Wansee (Germany),
but was built by Gewerkschaft Securitas (later: Chiffriermaschinen AG),
also of Berlin. This machine was known as
Die Handelsmaschine.
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There were a lot of problems with the printing Enigma machines.
The first ones had reliability problems with the print wheel
and the later model with the type bars. More importantly though,
they were extremely expensive to build and would only be suitable
for the high-end market.
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For this reason, Scherbius developed a machine that produced its output
on a lamp panel rather than on paper. The first model was the
Enigma A
that was introduced in 1924. It was also known as Gluhlampenmaschine
(glow lamp machine).
The machine was available for about 1/8th of the price of the printing Enigma
and costed RM 1000 1 . The machine is housed in a wooden case
and looks pretty much like the later Enigma models, except that the keys
are arranged in sequential order
(ABCDE...) rather than the more common typewriter order (QWERTZ...).
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The standard Enigma C
has 26 keys (A-Z) for the input and 26 lamps
(A-Z) for the output. The text is scrambled by means of three cipher wheels
that protrude the top lid. Each cipher wheel has 26 contacts at either side.
Several variants of the Enigma C were produced, such as the so-called
Funkschlüssel C (for the German Navy) and a Swedisch variant,
both with 28 keys.
➤ More about Enigma C
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The currency in Germany in 1924 was the Reichsmark (RM).
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Unlike the printing Enigma, the glowlamp machines had a reflector (UKW)
that made the machine reciproke (symmetric). As a result the settings
of the machine for encoding and decoding were identical, which greatly
improved its usability. The UKW had two or four fixed positions.
The idea for the reflector came from Scherbius' colleague Willy Korn,
who would later lead the company.
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In 1926, the design of the glow lamp Enigma was drastically improved.
A new chassis was developed and the standard (German) keyboard layout
(QWERTZ...) was introduced. Furthermore the reflector (UKW) could be set
to 26 different positions. It was mounted to the left of the three cipher
wheels, which is why this machine is sometimes thought to be a 4-wheel
Enigma.
The machine was internally known as model A26 and became known as
the Enigma D. Like the Enigma C it was housed in a wooden
transit case with a hinged lid. It had several improvements.
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The wheels could be accessed more easily (i.e. the top lid could be
opened), there was an optional sunlight filter for the lamp panel, and
it had a power selector that was mounted to the right of the cipher wheels.
The Enigma D became the basis for most of the later machines.
➤ More about Enigma D
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In 1927, a series of new developments were started, all based on the
chassis of the Enigma D.
First of all there was the Commercial Enigma,
that later became known as the Enigma K.
There were several variants of this machine, such as the
Swiss K that was built for the Swiss Army.
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All commercial Enigma machines had a simple wheel turnover mechanism
that is comparable to the odometer of a car. The rightmost wheel makes
a single step on each key press. After the rightmost wheel has completed
a full revolution, the middle wheel makes a single step and so on.
At the same time (1927) the development of a more advanced range of
machines was started. This range became known as
Zählwerk Enigma
(counter Enigma) or Zählwerksmaschine
(counter machine), probably because
it has a counter that shows the length of a message (key presses).
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Furthermore, the Zählwerk Enigma
has a far more advanced wheel turnover
mechanism that is driven by cogwheels rather than by pawls and levers.
This allows the mechanism to run in reverse direction as well,
which is useful for correcting mistakes. The Zählwerk Enigma also introduces
the concept of multiple turnover notches, which causes more frequent
(irregular) wheel stepping.
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The three cipher wheels have 11, 15 and 17 turnover notches respectively,
each of which are relative primes of 26, which increases the period of the
machine (i.e. the number of steps before the sequence is repeated).
Furthermore, the reflector (UKW) is now part of the stepping mechanism and
is driven by the other wheels.
The first Zählwerk Enigma was the model A28.
It was introduced in 1928 and was built on the chassis of the Enigma D.
A few years later, a design variant of the A28 was developed.
It was slightly smaller and had smaller cipher wheels.
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Although the number and position of the turnover notches was identical
(11, 15 and 17), the diameter of the wheels was smaller and the cogwheel
driven mechanism was slightly simplified. This machine was introduced in
1931 and was known as model G31
(later: Abwehr Enigma).
➤ More about Zählwerk Enigma
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Apart from the Zählwerk Enigma,
there is also a less well known version
of the machine that is suitable for numbers only. It is introduced in 1930
and is known as Enigma Z or Z30.
Two variants of this machine are known:
one with a simple stepping mechanism and one with Zählwerk stepping.
The machine was short lived and only a few units (±50) were ever built.
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In 1926, the German Army (Reichswehr, later: Wehrmacht) started showing
an interest in the machine. At their request a special variant of the
commercial Enigma D is developed. It has three cipher wheels and a fixed
reflector (UKW).
Furthermore, the new machine has a plugboard (Steckerbrett)
at the front that adds an extra layer to the cipher.
The Steckerbrett can be configured in the field and is used
exclusively for the Reichswehr. The first prototype is ready in 1927
and features a single-ended plugboard. It is known as the
Reichwehr Enigma D.
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The final version is ready in 1932 and has an improved double-ended
Steckerbrett. This version is known by the Reichswehr
(now: Wehrmacht)
as the Enigma-I and is only available to the Army.
Until this time, all commercial Enigma models were freely available on
the (international) market. This changes when in 1932 the German Army
claims the exclusive rights to the machine. From then on,
all commercial and international sales had to be approved
by the German Army.
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Apart from the Enigma-I,
the manufacturer – by then renamed Heimsoeth & Rincke –
also made a new version of the printing Enigma.
It is ready in 1929 and is the successor to the
Schreibende Enigma. The machine
is called Enigma H (model H29)
and is known by the Army as Enigma-II.
The Enigma H is also sold to the Hungarian Army, but was never very
popular due to its high price. Apart from the Hungary Army, the Germans
also kept selling Enigma machines to the Swiss and to the Dutch Army.
The latter also bought Enigma G31
models as late as 1938.
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In the mid-1930s the German Army is clearly preparing for war and
starts ordering Enigma-I machines in large quantities for the
Wehrmacht (Army) and the Luftwaffe (Air Force).
The Enigma G is used by the German Abwehr (secret service).
For the Kriegsmarine (German Navy) a model similar
to and compatible with the Enigma-I is developed.
It becomes known as the Enigma M1 (1934)
which is later followed by the Enigma M2 (1938)
and finally the Enigma M3 (1940).
➤ More about Enigma-I
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The first Enigma machines were developed in 1923
by Arthur Scherbius' first company Scherbius und Ritter
but were built after the company had been renamed first to
Gewerkschaft Securitas and a few years later
to Chiffriermaschinen AG. 1
After Scherbius' untimely death in 1929, the company changed
hands, and in 1933, after the German Army had acquired the manufacturing
rights to the Enigma machine, the name was changed once more
to Heimsoeth und Rinke.
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1918 Arthur Scherbius 1918 Gewerkschaft Securitas 1920 Scherbius und Ritter 1920 Chiffriermaschinen Aktiengesellschaft 2 1933 Heimsoeth und Rinke
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As many Enigma machines were needed for the German war effort,
other companies were contracted to build the machines under
licence. This also reduced the risk of supply problems should
any of the manufactures be bombed by the Allies.
With Heimsoeth & Rinke in Berlin being the engineering company,
the machines were manufactured by Konski & Krüger in Berlin.
Later, the military machines were also manufactured by
Olympia in Erfurt,
Ertel-Werk in München and,
Atlas-Werke in Bremen, all under licence of Heimsoeth und Rinke.
➤ List of manufacturers
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The History of Scherbius' first companies is very clouded.
The three companies:
Gewerkschaft Securitas, Scherbius und Ritter
and Chiffriermaschinen AG,
seem to have existed more or less simultaneously,
as patents were filed
by all three companies during the first years, at least until 1923.
It appears that from 1924 onwards, the name Chiffriermaschinen AG
prevailed.
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In their article in Cryptologia of January 2002 [9],
Kruh and Deavours state that
Chiffriermaschinen AG was established on 9 July 1923.
It is doubted whether this is correct however, as patent DE425147
was filed by Chiffriermaschinen AG on 26 September 1920,
which means that the company already existed back then.
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The Polish Breakthrough (1933)
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Around 1930, the Polish Cipher Bureau, Biuro Szyfrów, is the first
to make an attempt to break the Enigma cipher. As one of the closest
neightbours of Germany, they are very much aware of the clear and present
danger of another war. They start researching the commercial Enigma.
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From the University in Poznan, three young brilliant mathematicians
are recruited: Marian Rejwski, Jerzy Rózycki and Henryk Zygalski.
They start working on the Enigma cipher with nothing more that a
handfull of intercepted messages and a description of a commercial Enigma.
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Rejewski is set to work on the problem in late 1932 and after a few
weeks he achieves his first breakthrough, when he deduces the secret internal
wiring of the Enigma. Together with his colleagues he starts developing
various aids for the regular decryption of the German traffic.
Zygalski developed the so-called Zygalski sheets that were used to
exploit the double-enciphered message indicator 1 ,
a weakness in the German procedures. Later a machine is developed to
exploit this weakness mechanically: the
Bomba kryptologiczna
(the cryptologic bomb).
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With only three wheels available for the Enigma-I, there are 6 possible
wheel orders. On the Bomba, six sets of Enigma wheels are driven
simultaneously by a cog wheel at the center. Around 100 intercepted messages
were needed to recover the wheel order and initial settings.
➤ More about the Bomba
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The double-enciphered message indicators — that had enabled the Poles
to break a significant part of the Enigma traffic — dates back to the late
1920s. It was part of a proposal on how to use the commercial Enigma.
In early 1940, newly hired mathematicians at OKW/ln7 discovered the
weakness that it introduced. The procedure would eventually be
abandonned by the Germans on 1 May 1940, but by that time WWII had already
started and the British had beome involved in codebreaking (see below) [10].
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In 1933, the Polish Cipher Bureau even gets access to the Enigma operating
procedures that are used by the German Army. Hans Thilo Schmidt, a German
playboy working at the German Cipher Office, is in need of money and sells
infomation to the French secret service. The French, who gave Schmidt the
codename Asché, pass it on to the Poles,
who can now reconstruct the machine.
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From 1933 onwards, the Poles intercept and decrypt a significant
portion of the German radio traffic. In 1938 they see an increase
in the number of messages sent by the Germans and it seems clear that
Germany is preparing for war.
All this time, the Germans have been using a common Grundstellung
(basic setting) for all Enigma traffic. On 15 September 1938 however,
this procedure is abandonned. Around the same time, two new wheels
(IV and V) are added to the existing three, which multiplies the
maximum number of possible settings by a factor of 10.
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In the meantime, the Poles have built their own equivalent of the
Wehrmacht Enigma with a plugboard added towards the rear.
The wiring of the two additional wheels is soon recovered by Rejewski
and suitably wired wheels are added to the Polish Replica. With the
war imminent, the Poles start looking for ways to get their knowledge
out of the country before it is too late.
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Dillwyn (Dilly) Knox
was one of the Room 40 codebreakers during
World War I.
Since 1925 he had been trying to break the Enigma machine and had his first
success on 4 April 1937 when he broke Franco's
Enigma K during the Spanish Civil War.
When Germany starts using the Steckered Enigma
for communication between Germany and Spain in 1938,
he mounts an attack on the military Enigma, but is not
successful as he unable to work out the wiring of the entry disc (ETW).
In 1938, the British GC&CS starts discussing the Enigma machine with the
Deuxième Bureau, the French cipher bureau, from whom they acquire the details
that the French had obtained from the German spy Asché.
The French also dislose their contacts with the Poles.
In January 1939, at the first Polish-French-British meeting in Paris (France),
GC&CS is represented by Dilly Knox,
Hugh Foss and Alastair Denniston.
Dilly describes the system of rodding that he had developed, but the Poles
were instructed by their superiors not to disclose any vital information
at this time.
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Dilly had clearly impressed the Poles and on 25-26 July 1939,
with the war imminent, a second meeting was arranged, this time in Poland at
a facility of the Polish Cipher Bureau in a forest near Pyry, south
of Warsaw (Poland). At this meeting, the Poles revealed their achievements.
Also at this meeting, the Poles gave a
replica machine
to both the French and the British.
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Rejewski had used a different approach to Knox, as he used (mathematical)
permutation theory to solve the problem, whilst Knox applied linguistics.
Nevertheless, the two quickly established a good relationship during
the conference. Knox also learned that the Enigma entry disc was simply
wired in alphabetical order. Something that neither he nor
Alan Turing had ever considered.
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The meeting in Pyry was attended by Dilly Knox
as codebreaker, Alastair Denniston
as head of GC&CS (and codebreaker), and Humphrey Sandwith
as head of the Admiralty's intercept and direction-finding service.
On behalf of the French Deuxième Bureau, Captain Gustave Bertrand was present.
The Polish contribution would soon prove to be of vital importance
to the war effort.
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Immediately after the meeting, the Polish Cipher Bureau
destroys all its secret documents and equipment, whilst
the cryptanalysts escape to France.
A few weeks later, on 14 August 1939, Bletchley Park
is established by the British.
Only two weeks later, on 1 September, Germany invades Poland and
two days after that, on 3 September, Great Britain and France
declare war to Germany. World War II has started, just five weeks
after the Poles had shared their secrets. In the early stage of
the war, the Poles continue to work on Enigma from the French
Cipher Bureau.
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Bletchley Park
is an estate in the small town of Bletchley
(Milton Keynes, UK), some 45 miles north of London, that would become
the home of the
Government Code and Cypher School (GC&CS),
the British Cipher Bureau. The location
was choosen because it had direct railway connections to London,
Cambridge and Oxford, allowing scientists and army personnel to travel
unobtrusively.
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The first people to arrive at Bletchley Park (BP) are professional
codebreakers, mathematicians, chess players and people with
organising skills. Among them are
Dillwyn (Dilly) Knox,
Gordon Welchman,
Alan Turing
and Stuart Milner-Barry.
Knox had already worked for the codebreaking unit Room 40 during World
War I, and helped with the decryption of the famous
Zimmermann Telegram which brought the US into the war.
Stuart Milner-Barry was a chess player and chess writer. Gordon Welchman
and Alan Turing both were mathematicians from Cambridge (UK).
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Initially, Enigma messages are broken 'by hand', using simple pencil
and paper methods, and with additional tools such as the so-called
Jeffrey Sheets, the British equivalent of the
Polish Zygalski Sheets. But as the volume of the traffic
increases, Turing starts looking for automated solutions.
Based on the Polish Bomba
and the information that was passed by
the Polish codebreakers shortly before the start of WWII,
Turing develops the Bombe.
Although the Polish method of exploiting
the German weakness of the double-encypered message indicator
could no longer be used, Turing developed a more universal method
based on Cribs
(pieces of guessed plain text).
➤ More about the Bombe
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The British Prime Minister, Winston Churchill, fully recognizes
the value, impact and importance of the intelligence delivered
by Bletchley Park (BP) and its codebreaking apparatus. He introduces a new
level of secrecy that superceedes all other levels: Top Secret Ultra,
commonly abbreviated to ULTRA, and states that the source of this ULTRA intelligence
has to be kept secret at all cost.
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In the first stages of the war (1940), the British codebreakers are
able to read the majority of radio messages from the German Air Force
(Luftwaffe) and a modest part of the Army traffic (Wehrmacht). The
Naval messages on the other hand, impose a real problem as their operating
procedures are much more complicated.
Furthermore, the German Navy (Kriegsmarine) uses three additional rotors
(VI, VII and VII)
of which the wiring was hitherto unknown. These extra wheels are used
exclusively by the Navy and are not shared with other parts of the Army.
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In 1941, Turing achieves a breakthrough when he is working in isolation
in The Cottage at BP.
He discovers the wiring of the additonal wheels
and the naval message indicator procedure. Aided by the catch of a large
amount of codebooks from U-Boot U-110, that was captured on 9 May 1941,
Turing manages to find a way into the Naval Enigma M3 and to decrypt part of
the naval traffic.
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Apparently, the Kriegsmarine uses a complex procedure that involves
several codebooks, short message books and substitution tables.
Long messages and status reports are shortened by translating them
into a short letter combination.
The British even develop a unique system for
direction finding, known
as HFDF
(or Huf-Duf),
in order to obtain useful cribs for the Bombe.
Then, on 2 February 1942, disaster strikes when the German Navy,
completely out of the blue, introduces a new Enigma machine. It causes
an immediate black-out for the BP codebreakers.
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The new machine has an extra cipher wheel that is inserted
between the leftmost wheel and the reflector. At the same time,
the indicator system is changed and new codebooks are introduced.
The new machine is known as the Enigma M4
and is used exclusively
by the U-Boot section of the Kriegsmarine. The Bombes,
that are made for the 3-wheel Enigma, are not suitable for this.
➤ More about Enigma M4
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The Battle of the Atlantic
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During WWII, there was en enormous shortage of nearly everything in the UK.
Large convoys of supply ships, the so-called Liberty Ships, travelled from
the USA to the UK, bringing people, food, ammunition and anything else that
was needed, to wartime Britain and to the Soviet Union [6].
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Althoug the Liberty Ships were designed in the UK,
they were adapted by the US and were quick and cheap to build.
The convoys were often protected by military vessels.
Nevertheless they were an easy prey for the German U-boats that were
organised in the so-called Wolfpacks.
The 4-wheel Enigma M4
had a serious impact on The Battle of the Atlantic.
As it was no longer possible to read the messages to and from the U-boats,
it was impossible to determine the location of the Wolfpacks,
resulting enormous losses of ships, people, supplies and war cargo.
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The black-out that started on 2 February 1942, lasted for nearly nine
months and costed, no doubt numerous, lives. Luckily however, the tide
changes on 30 October 1942, when new codebooks are captured from a sinking
U-boat. In the meantime, Turing has worked out the new Naval procedures
and the wiring of the additional wheel. The codebooks complete the puzzle.
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As the Bombe
was only suitable for attacking 3-wheel Enigma machines,
several solutions were developed. A 3-wheel Bombe, that contained the
equivalent of 36 Enigma machines, was modified into a 24-Enigma
4-wheel Bombe. Although the resulting machine was rather slow, it worked.
A better solution was to add external 4th-wheel attachments
to the existing 3-wheel Bombes. Such add-ons were developed and built by
the British Tabulating Company (BTM) as well as by the General Post Office
(GPO) at Dollis Hill. Some solutions even involved valve-based technology.
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Finally, several variants of a true 4-wheel Bombe were built.
Some of these featured an extra fast 4th wheel and an electronic
valve-based sensing circuit that was developed by
Tommy Flowers
at the GPO in Dollis Hill.
By this time, the US had already entered the war and after a long
discussion it was decided to share the knowledge about the Bombe technology
with the American Allies.
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This decision — that allowed the Americans to develop their own
4-wheel Bombe — came just at the right time. As the UK suffered
shortages of nearly all kinds of material, it became more and more
difficult to build reliable machines.
The Americans on the other hand, had sufficient supplies and
resources and were able to allocate funding and production capacity
to it. The US Bombe was developed by Joe Desch, an engineer at the
National Cash Registers (NCR) in Dayton (Ohio).
Development started at the end of 1942 and by mid-1943 the first
US Bombe was ready.
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It appeared to be much faster the UK Bombes and involved valve-based
electronic circuits.
By the end of 1943, no less than 120 machines were installed and
for the remainder of the war, the US took care of breaking the bulk of
the 4-wheel based Enigma messages (i.e. the U-boat traffic), leaving
a modest part of it, plus the bulk of the 3-wheel traffic, to the
codebreakers in the UK.
➤ More about the US Bombe
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The most common version of the Enigma machine that was broken by the
codebreakers at Bletchley Park (BP) was the Enigma-I,
the machine that was used by the German Army and Air Force.
The Naval machines, the M3
and M4, were also broken on a regular basis. Nevertheless,
there were other Enigma models and variants that arequired
the BP codebreaker's attention.
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Some less important networks, sometimes used Commercial
Enigma machines. Such machines, generally the Enigma K,
were also used by other countries,
such as Italy, Spain and Switzerland.
One of the most difficult machines to be broken, appeared to be
the Enigma G. It was a variant of the commercial Enigma
that had a cog wheel driven mechanism and multiple turnover notches on
each wheel, causing irregular wheel stepping.
Such machines were used by the German Secret Service,
the Abwehr
(hence the nickname Abwehr Enigma) and could not be broken by the Bombe.
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The Abwehr networks yielded far less intercepts than the regular army
networks, making it very difficult to find any messages in depth.
Furthermore, the Abwehr used different keys on each link, requiring
each radio link to be broken individually.
The Enigma G was attacked by a team led by
Dillwyn (Dilly) Knox,
who had worked in the Room 40 codebreaking unit during World War I.
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Knox had helped to decrypt the Zimmermann Telegram which was responsible
for bringing the USA into WWI. After WWI he joined
GC&CS and as a cryptographer
he was amoung the first group of people to arrive at
Bletchley Park in
August 1939, where he started working in
The Cottage.
After breaking the Italian Naval Enigma in 1941, something that was
decisive in winning the Battle of Matapan (Greece), he and his group of
female codebreakers (known as Dilly's Girls) started working on the Abwehr
Enigma, and by the end of 1941 they had their first success.
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After the first breakthrough in October 1941, a special unit was established
to work on the Abwehr decrypts. It became known as
Intelligence Services Knox (ISK)
and by the end of the war, ISK had processed about 140,800 Abwehr messages [7].
Knox himself didn't live to see the results of his work.
Already diagnosed with lymph cancer at the start of the war,
he died in February 1943.
One of 'his girls' — top codebreaker
Mavis Lever (later: Batey)
who had broken the Italian Naval Enigma in 1941 —
wrote an affectionate biography about
Dilly Knox
in 2009 [8].
➤ More about Abwehr Enigma
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Before and during World War II, Japan was arguably Germany's most
important ally. Germany mainly fought their war in Europe, North
Africa and Russia, whilst Japan took care of the southern hemisphere.
During the war, Japan had observers in all parts of the European war theatre.
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For communication between the observers and their headquarters,
the Japanese used two manual cipher systems, known as Sumatra
and TOGO (later: Sumatra 2 and TOGO 2), but they preferred a mechanical
system like the Enigma.
Although they preferred the Military Enigma I
(with Steckerbrett),
the Germans didn't want to give away their most secure Enigma machine.
Instead it was agreed in 1942 to build a special version of the
commercial Enigma K
with a differently wired entry disc (ETW)
and five turnover notches on each of the eight wheels.
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The Japanese ordered 800 of these machines and the first units
were delivered to them in August 1943.
Due to material shortages however, the full order was never delivered.
Furthermore, the Japanese had their doubts about the security of the
commercial machine and insisted to have the military variant instead.
In the end it was agreed that the remainder of the order would
consist of military Enigma-I
machines that were backwards compatible with the
Enigma T.
➤ More about Enigma T
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In retrospect it may seem strange that the Germans kept using
Enigma for so long and that its security was never questioned.
In reality however, questions about the relibility of Enigma had
been raised on several occasions, for example by U-Boat commander
Admiral Karl Dönitz.
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On each occasion, the Army Intelligence Service, (Abwehr)
was asked to investigate any incidents. But the Abwehr,
who had been responsible for choosing the Enigma in the first
place, always concluded that it was imposible to break the machine.
After all, the British used it as well...
Nevertheless, Donitz kept having doubts and took his own measures.
Three additional cipher wheels (VI, VII and VIII) were introduced
in 1939 for exclusive use by 'his' Navy and in 1942, out of the
blue, he introduced the M4 Enigma.
But these were not the only security measures.
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In 1943, a new reflector Umkehrwalze C or UKW-C
(with 4th wheel 'Gamma')
was introduced as an alternative to UKW-B, but it was only
available to a limited number of users.
Nevertheless it was used until the end of the war,
sometimes even mixed with UKW-B and 4th wheel 'Beta'.
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In January 1944, a rewirable reflector,
UKW-D
or Dora, was introduced. It could be fitted in place
of the existing UKW-B and there even was a special Naval version of it.
Codebooks were updated to include the UKW-D wiring, which was
changed every 10 days. Nevertheless UKW-D
saw limited use as it was difficult in operation
and could not be distributed effectively in 1944.
The German Air Force, the Luftwaffe, took their own
measures and developed a device to alter the wiring
of the Steckerbrett (plugboard) for each message. It was known
as the Enigma Uhr.
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The Uhr
was a small wooden device that could be attached to
the right side of an Enigma machine and had 20 wires that
were connected to the Steckerbrett instead of the
normal patch cables. A large wooden knob on top of the device
could be set to any of 40 positions, marked 00 - 39.
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The Uhr was even combined with UKW-D
on the so-called Red key,
making it a real challenge for the codebreakers at Bletchley Park.
Had the Uhr been used correctly, it might even have defeated them,
but due to operator mistakes it was broken within a few days
after its introduction.
By far the most dangerous Enigma improvement however,
was the so-called Lückenfüllerwalze
(gap-filling wheel). It had been developed in
1943 by Regierungs-Oberinspektor Menzer,
but was put off several times as the Enigma was still
considered to be a secure machine at the time.
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Towards the end of the war 12,000 of these wheels were ordered.
The Lückenfüllerwalze
is a normal Enigma cipher wheel, with programmable turnover
notches, 26 in total.
It can easily be configured in the field and causes irregular
wheel stepping, something that could have defeated the codebreakers.
But the war ended before it was ready for release.
After the war, the American TICOM immediately confiscated the
Lückenfüllerwalze and kept it under wraps for many years.
➤ More about UKW-D
➤ Enigma Uhr
➤ Luckenfüllerwalze
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The Enigma wasn't the only rotor-based cipher machine that was used
during World War II. The UK used the so-called
Typex cipher machine
for all high-grade traffic. The Typex, which was virtually a plain copy
of the German Enigma, had five cipher wheels, three of which were moving.
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As far as we know, Typex
was never broken by the Germans during the war,
despite the fact that the Germans had captured some machines. The discovery
that the British used a machine similar to the Enigma, confirmed their
believe that the machine was indeed unbreakable.
The Americans also used a rotor machine for some of their radio traffic.
Whilst the Hagelin M-209
was used for tactical field messages,
it was known to be broken by the Germans. For high-grade traffic however,
the advanced 15 rotor
SIGABA machine, shown here, was used instead.
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It was a combined development of US top cryptographers William Friedman,
Frank Rowlett (US Army) and Laurence Safford (US Navy). Although the machine
was clearly based on the design of the Enigma, it was improved in many
areas and was able to print its output onto a paper strip.
As far as we know, SIGABA was never broken by the Germans during the war.
In the latter part of the war, around November 1943, the need arose for the
Americans and the British to securely exchange cipher messages.
As they couldn't agree on which machine was the better one,
Typex
or SIGABA,
it was decided to define a common standard and modify both
machines to comply with that standard. The common machine became known
as Combined Cipher Machine (CCM).
➤ More about Typex
➤ SIGABA
➤ CCM
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Once the war was over, the entire story of breaking the Enigma machine
was kept secret for many years. Apart from a few exceptions, people went
on with their lives and most of the Bombes
were dismantled. The captured
Enigma machines ended up in the vaults of
CG&GS
(now: GCHQ)
and the NSA,
or were given to other countries with the message that
they could not be broken.
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In countries like Norway, Germany and Austria, the
Enigma-I was used
for many years after the war, until they were replaced by newer
and better equipment. It is believed that the machine was also used in
several African countries.
Funnily enough, there are no reports about the use of Enigma by the
Russians, although it is pretty certain that they must
have captured some machines. For a long time it was assumed that the
Russians had no knowledge about the Allied codebreaking achievements of WWII,
but it now seems likely that they were well informed.
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In 1956, the Russians introduced the first version of a very advanced
rotor-based cipher machine that was codenamed
FIALKA. The machine had 10 cipher wheels
and featured irregular wheel stepping, with the wheels moving in both
directions. More importantly, they had found solutions for all Enigma's
weaknesses, such as the fact that a letter can never be encoded into itself.
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Furthermore, the Steckerbrett was replaced by a card reader and the machine
operated directly on teleprinter signals, allowing the use of letters
and numbers.
It had a built-in tape puncher and reader,
and printed the output directly onto a paper strip.
It was officially known
as M-125
and was used by all countries of the Warsaw Pact.
Shortly after the end of WWII, the Americans started the
development of a new rotor-based cipher machine that would replace
SIGABA. The machine became known as
KL-7,
and also by its key-procedure
names ADONIS and POLLUX.
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The KL-7 was not only used by the USA,
but also became the main cipher machine of the newly established
NATO in the post-war era.
Boris Hagelin,
the developer of the US
M-209
cipher machine, moved from Sweden
to Switzerland and introduced a long range of
pin-wheel based cipher machines
during the 1950s. In the 1960s, rotor-based cipher
machines were gradually replaced by fully electronic cipher machines,
such as the KW-7,
KG-84,
Ecolex 4
and Aroflex.
By the late 1980s, all machines had been replaced by a wealth of
modern equipment like the KIV-7.
➤ More about FIALKA
➤ KL-7
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Other WWII German Cipher Machines
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Enigma was by no means the only cipher machine used by the
Germans during WWII. In fact the Enigma, of which over 20,000
units were produced, was mainly used at a tactical level, whilst
the German High Command (OKW) used other machines, such as
the Siemens T-52 Geheimschreiber
and the Lorenz SZ-40/42 teleprinter add-on.
Towards the end of the war, they even started using the
Siemens T-43,
a machine that was based on the
unbreakable One-Time Pad cipher.
Furthermore, it was decided that the Abwehr Enigma would be replaced
by the SG-41, also known as the Hitlermühle (Hitler Mill),
an improved version of the Hagelin
C-38/M-209,
developed by Fritz Menzer. It was avalable
in an alphabetical and a numerical variant, but came too late to
have a significant effect on the course of the war.
Only a handful of the above machines have survived.
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Based on many years of research by Frode Weierud, we've been able
to put together the most accurate family tree of Enigma machines to date.
It shows the relationship between the various models and variants,
and provides a lot of additional information.
Please note that the tree is based on ongoing research and is therefore
subject to changes.
➤ More information
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The history of the Enigma machine is extremely complex.
There were many different models and variations,
and they were used by many different customers.
During the war, a mixture of military and commercial
Enigma machines were used by different branches of the
war aparatus.
Based on the above research, we've created a timeline
of events, patents, enigma models, accessories and peripherals.
➤ More information
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- Wikipedia, Rotor machine
Retrieved January 2014.
- Karl de Leeuw, The Dutch invention of the Rotor Machine, 1915-1923
Cryptologia, January 2003, Volume XXVII, Number 1, pp. 73-94.
- Wikipedia, Enigma machine
Retrieved January 2014.
- Dutch Patent NL10700
7 October 1919. Transferred to Securitas on 5 May 1922. 1
- Dr.-Ing. Arthur Scherbius. Enigma Chiffriermaschine
Elektrotechnische Zeitschrift. 1923. Heft 47/48. p. 1035-1036.
- Wikipedia, Battle of the Atlantic
Retrieved January 2014.
- Wikipedia, Dilly Knox
Retrieved January 2014.
- Mavis Batey, Dilly, The Man Who Broke Enigmas
2009. Hard cover, ISBN 978-1-906447-01-4.
- Kruh and Deavours, The Commercial Enigma: Beginnings of Machine Cryptography
Cryptologia, Volume XXVI, Number 1, January 2002.
- Frode Weierud, Personal correspondence
August 2017.
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The rights to patent NL10700 were transferred to Naamloze Vennootschap
Securitas in Amsterdam (Netherlands) on 5 May 1922 and then to
Chiffriermaschinen AG in Germany on 28 January 1927.
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© Crypto Museum. Created: Wednesday 14 March 2012. Last changed: Saturday, 16 April 2022 - 07:32 CET.
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