The story of the famous Enigma cipher machine combines
ingenious technology, military history and the mysterious
world of espionage, codebreakers and intelligence into a
real thriller. Never before has the fate of so many lives
been so influenced by one cryptographic machine, as in
the Second World War. Enigma is the most famous and
appealing example of the battle between codemakers and
codebreakers. Enigma showed the importance of
cryptography to military and civil intelligence. All
images copyright D. Rijmenants. Click the images to view
them in higher resolution.
Origins of
the Enigma
The need for secure
communications for both military as civilian use
became obvious in the early 1900s, with the rise
of wireless communication. The search to replace
the impractical and time-consuming hand ciphers
began. In 1917, the American Edward Hugh Hebern
developed a cipher machine with rotating disks,
each disk performing a substitution cipher.
Hebern's idea was the base for many similar
machines, developed in several other countries.
In 1918, Engineer Arthur
Scherbius patented a cipher machine using rotors.
The German Navy and Foreign Offices were
approached, but were not interested. In 1923, the
rights for the patents went to
Chiffriermaschinen-AG, a firm with Scherbius on
the board of directors, that commercialized the
machine. In 1927, Scherbius bought the 1919
patent from of a similar machine from the
Dutchman Koch, in order to secure his own patent,
approved in 1925.
The first cipher machine,
Enigma A, came onto the market in 1923. It was a
large and heavy machine with an integrated
typewriter and weighed about 50 Kg. Soon after
the Enigma B was introduced, a very similar
machine. The weight and size of these machines
made them unattractive for military use. The
development of the reflector, an idea of
Scherbius' colleague Willi Korn, made it possible
to design the compact and much lighter Enigma C.
Also, the type writer part was replaced by a lamp
panel. In 1927, the Enigma D was introduced and
commercialized in several versions with different
rotor wirings, and sold across Europe to military
and diplomatic services. The Enigma D had three
normal rotors and one reflector that could be set
in one of the 26 positions.
Several intelligence services
succeeded in breaking the civil and military
Enigma versions which were all based on the
commercial D. The Enigma D had no plugboard, a
military feature that would increase security
considerably from 1935 onwards. The Italian Navy
bought the commercial Enigma D, as did Spain
during the Spanish Civil War. The Swiss army used
the Enigma K, a slightly modified version of the
Enigma D. Japan used the Enigma T, also called
Tirpiz Enigma, an adapted Enigma D with modified
entry rotor connections. Japan also developed
their own version of the T, with horizontally
placed rotors. The messages of both models T and
K were broken as well. The Railway Enigma,
another D clone wich was used by the German
Reichsbahn in Eastern Europe, was partially
broken from 1941 onwards.
In 1926, the commercial Enigma was purchased by
the German Navy and adapted for military use. They called
it Funkschlüssel C. Meanwhile, Chiffriermaschinen-AG
developed a special Enigma with rotors that have the same
contact alignment as the D rotors, but with teeth,
multiple notches and are advanced by cog wheels instead
of pawls and ratchets (see patent drawing left). It also
had a rotating reflector and a counter on its left. Only
one is know to exist today. This probably experimental
model, presented in 1928 but exceptionally only patented
in 1931, lead to the Enigma G. The Enigma G had different
rotors with a zigzag pin placement and the counter on its
right. Its rotors, which also had multiple notches, were
moved by a system of gears, similar to the 1928 special
predecessor. Already in 1928, the German Abwehr (Secret
Service) bought the 12 Kg light Enigma G, also called
Zahlwerk (clock-work) Enigma due to it's counter on the
front panel. The Enigma G was exclusively used by the
Abwehr.
In 1932, the Wehrmacht revised the
commercial Enigma D and added the plugboard at the front
of the machine. This version, the Enigma I, became known
as the Wehrmacht Enigma and was introduced on a large
scale in the Heer (Army) and public authorities. The
Luftwaffe (Air Force) followed the Heer's lead in 1935.
The Wehrmacht Enigma came initially with three rotors.
From 1939 on they were equipped with five rotors.
In 1934, the German Navy adopted the
Wehrmacht model, with its securer plugboard, and extended
the set of rotors to eight. The Navy machine was called
Funkschlüssel M or M3. In 1941, although reassured by
the Abwehr that the Enigma M3 was unbreakable, Admiral
Karl Dönitz insisted on improvement of the Kriegsmarine
Enigma. Early in 1942, the famous four rotor M4 model was
introduced in the Kriegsmarine.
During the war, different types of
reflectors were introduced. The B and C reflector were
used on Heer and Luftwaffe models, and also on the
Kriegsmarine M3. The Kriegsmarine M4 used a thin B and C
version, to fit in the 4 rotor machine, with other
wirings, but if 'zeroized' in combination with its fourth
rotor compatible with the Heer and Luftwaffe version. By
the End of the war German Command tried to introduce a
new type D rewirable reflector. Early use of this
reflector posed a significant problem to Allied
codebreakers, but problems in distribution of this
reflector and their key sheets prevented a widespread use
of the D reflector. Another military add-on, introducend
in 1944 by the Luftwaffe, was an extra plugboard switch,
called the Uhr (clock), a switch with 40 positions, each
position resulting in a different combination of plug
wiring. For more information about Enigma code books and
the message procedures, please visit the enigma procedures page. The technical details page
explains how the Enigma works and shows the inside of the
machine.
An estimated total of 100,000 Enigma
machines were produced. Although
generally know as Enigma, there were only a few machines
that actually carried the name Enigma and the logo. Most
machines only had a serial number and fabrication code.
The machines were produced in different factories on
various locations such as Ertel-Werk für Feinmechanik in
München, Olympia Büromaschinenwerke in Erfurt,
Chiffriermaschinengesellschaft Heimsoeth & Rinke in
Berlin, Atlas-Werke Maschinenfabrik in Bremen and Konski
& Krüger in Berlin. The machines that survived the
war were confiscated by the Allies and mostly sold to
other countries. The rotors of these machines were often
rewired. Of course, they forgot to mention that they were
able to break them.
When the Wehrmacht introduced
the plugboard on the military Enigma, this added
an astronomical number of possible key stettings.
The general idea was that this military Enigma,
unlike the commercial types, would be impossible
to break. No one even tried to break it. However,
in 1932, Poland's Biuro Szyfrow (Cipher Bureau)
initiated attempts to analyse and break the
Enigma messages. Although the chief of this
Bureau received copies of codebooks sold by the
German spy Hans-Thilo Schmidt, he did not give
them to his codebreakers. He thought that keeping
this information from them might stimulate their
efforts.
Marian Rejewski, Henryk
Zygalski and Jerzy Rozicki were convinced that
mathematics could solve the problem and succeeded
in breaking the Enigma messages. They also
developed an electro-mechanical machine, called
the Bomba, to speed up the codebreaking process.
Two major security flaws in the German Enigma
procedures were the global groundsetting and the
twice encodes message-key, a procedure to exclude
errors. These flaws opened the door to
cryptanalysis. In 1939 the Bureau was no longer
able to break the codes due to increased
sophistication in the design, new procedures and
lack of funds for the code breakers. When Germany
invaded Poland, the Polish Biuro Szyfrow passed
its secret knowledge and several replica Enigma
machines to the baffled French and British
intelligence. The work of the Biuro Szyfrow was
vital, not only because their pioneering work
itself, but also because it convinced other
cipher bureaus that it was possible to break
Enigma.
Bletchley Park
The Government Code and Cipher
School (GC&CS) at Bletchley Park initially
broke Enigma by hand. In August 1940 they started
using their own Bombes, designed by Alan Turing
and Gordon Welchman. It was also a rotary
electro-mechanical device but it worked on an
entirely different principle as Jerewski's Bomba.
The Turing Bombe searched for the enigma settings
for a given piece of plain and cipher text. When
an Enigma message was intercepted, codebreakers
had to search for so-called cribs. These cribs
were presumed pieces of plain text within the
encrypted message. This could be "An Der
Oberbefehlshaber", "An Gruppe",
"Es Lebe Den Fuhrer" or any other
standardized code (from code books) or piece of
text.
Once a crib was located
(special techniques existed to do this) the
associations between the letters of the
ciphertext and their plain version were entered
in the Bombe. The Bombe, which contains a large
number of drums, each replicating the rotors of
the Enigma, ran through all possible settings to
find the key settings that belong to the given
pieces of cipher and plain text. Once these
settings were found all messages, encrypted with
these setting, could be deciphered.
All information retrieved by
cryptanalysis, the breaking of codes, had the
codename “Ultra” and played a very
important and often decisive role during the war,
mainly in the Battle of the Atlantic. All Ultra
information was used very carefully, so as to
avoid suspicion among the German forces. Special
liaison officers, trained to deal with this
valuable but delicate knowledge, were placed in
Headquarters and other strategic places.
Moreover, Ultra was never used unless it could be
confirmed by a second source in order to avoid
giving the German Command reason to suspect that
their communications security might be broken.
The Kriegsmarine
The German Kriegsmarine was
very successful in applying their Rudeltaktik or
"Wolfpack Tactics" with U-boats. They
hunted individually for convoys. If a convoy was
spotted, they shadowed it and called other
U-boats into battle. Once all U-boats were on the
spot, they sank the convoy with a closely
co-ordinated attack. This technique was so
devastating to the allied supplies that it almost
decided the outcome of the war. Communication was
the keyword and the U-boats used Enigma to send
messages to co-ordinate their attacks. After some
initial hard times, Bletchley Park broke the
naval codes almost continuously.
Decreasing effectiveness of his
U-boats made Admiral Donitz suspicious and,
although reassured by German intelligence that
Enigma was secure, he insisted on improving the
Enigma's security. Early in 1942 the famous
4-wheel machine was introduced in the Kriegmarine
and the complicated 'Shark' codes caused a big
crisis at Bletchley Park. The Kriegmarine
referred to the spring of 1942 as the "Happy
Times" because the Allied forces were unable
to decipher the codes and the U-boats were able
to continue sinking ships without much
interference. More information is found on Enigma and
the U-boat War.
Turning the tide
The codebreakers in Blechtley
Park discovered by cryptanalysis that a fourth
rotor had entered the battlefield of codes. After
ten nerve-wracking months of heavy losses,
Bletchley Park succeeded in breaking the 'Shark'
codes. The major reason for this success was the
capture of Kurzsignal codebooks by British Navy
on German weather ships and the attacks on
U-boats like Kapitanleutenant Heidtmann’s
U-559 by HMS Petard. These boarding were not to
steal Enigma machines or key sheets, as often
wrongly portrayed in movies and books (they
already had replicas of the Enigma from the Biuro
Szyfrow). Enigma key sheets only gave access to a
particular radio net and area for a single month.
However, only two editions of
the Kurzsignal codebook, issued to all U-boats,
were ever printed during the war. These codebooks
encoded weather and operational reports in
four-letter codes, prior to encryption with
Enigma. By seizing them, Bletchley Park could use
these four-letter codes as new cribs to attack
all future Enigma setting. Moreover, new Bombes
were developed to deal with the four-rotor
Enigma, and by the end of 1943, another fifty of
these Bombes became operational in the US Navy.
More on the codebooks can be found on the enigma
procedures and Kurzsignalen pages.
The tide of the U-boat war had
turned. Except for some brief periods, the entire
communication system was intercepted by a large
number of listening stations, and the message
were broken in Bletchley Park, which employed
over 7000 workers at its peak. With the positions
of the U-boats unveiled, Allied ships could now
evade the U-boats and the Allies actively hunted
for U-boats. The elite weapon of the Kriegsmarine
got decimated, with heavy losses among the U-boat
crews. An estimated 700 U-boats and 30,000
crewmen were lost at sea. U-boat command never
suspected cryptanalysis of the Enigma and related
these losses to new Allied submarine detection
techniques like ASDIC sonar, surface radar, HF
direction finding and anti-submarine airplanes.
All improvements, introduced by
the German Forces, were tackled successfully by
the codebreakers. The introduction of the
rewireable D reflector, with its key changes
every ten days, proved to be a big problem to the
codebreakers. A widespread use of the D reflector
would require five to ten days to break a
particular key, which would render tactical
information useless. Without the D reflector,
keys were broken mostly within 24 hours.
Fortunately, logistical problems prevented
general use of the D reflector in the German
forces. Also, German operators were reluctant to
use the D reflector and found it too elaborate to
program in tactical situations. Instead, the B
reflector remained the default reflector and the
D reflector was used only for important messages,
on the same machines with the same basic machine
settings for rotors and plugboard. However, with
the key already broken for these machines with
the B reflector, the codebreaker only had to
retrieve the unknown wiring of the D reflector,
used on the same machines. A work that was
performed by hand.
The fatal mixed use of B and D
reflectors enabled the codebreakers to continue
reading the once feared D reflector messages. The
Enigma Uhr (clock), used by the Luftwaffe, was
another useless effort by the Germans to increase
the security of the Enigma. The Uhr was a switch
that replaced the plugs of the Enigma and
provided 40 different plug wirings. However, the
unique design of the Allied Bombes, used to
retrieve the key settings of the Enigma, excluded
the plugboard wiring. The Enigma Uhr therefore
had little or no effect on the codebreaking
results.
The ULTRA information
was kept highly secret during the entire war and played a
decisive role. Breaking the Heer and Luftwaffe messages
also provided crucial tactical information. The
codebreakers exposed the weakness of Field Marshal
Rommel's notorious Afrika Korps. The speed and success of
the Afrika Korps created long stretches of poorly
defended supply lines. ULTRA information revealed their
logistical problems and provided Field Marshal Montgomery
with a vital tactical advantage. In the days before the
D-day invasion of Normandy, the Wehrmacht, without
realizing it, provided the Allies with an enormous
quantity of detailed information on the coastal defences,
location and strength of all German tank divisions and
the movement of troops in France. Experts estimate that
the breaking of Enigma shortened the war by about three
years. The number of saved lives is innumerable. The
large scale breaking of German communications was one of
the best kept secret of the Second World War. German
armed forces kept on using Enigma during the entire war
without any suspicion
How secure was the Enigma machine
actually and why ended it up being the Achilles heel of
the superior German war machine? During a top secret
Allied operation in the final days of the war, special
TICOM teams round up German cryptologists and Signals
Intelligence personnel. The answer to our question is
found in their only recently declassified TICOM reports,
vol 2, “Notes on German High Level Cryptography and
Cryptanalysis” (see this link NSA website).
Summarized, it comes to this: to create
a secure crypto device you need both excellent codemakers
and codebreaker. You cannot effectively assess the
security of a crypto machine unless you test it by trying
to break it. According to TICOM, Germany had very capable
cryptologists and developed some excellent crypto
machines. Unfortunately, their codebreaking skills,
although excellent, were not on par with their brilliant
Polish, British and American counterparts.
It was this little difference in
codebreaking skills that convinced the Germans that
Enigma was secure. Their studies only revealed
theoretical weaknesses. It was the same little difference
in skills that enabled the Allies to find a practical
solution to the theoretical weaknesses of the Enigma
machine. German cryptologists did continue to develop
various improvements to Enigma and other crypto machines
during the war, some of which, according to TICOM
reports, would prove impossible to break by the Allies at
that time. Fortunately, as the war progressed, logistical
problems, shortage of raw materials and lack of time and
money kept these new machines from entering service.
The heritage of Enigma
After the Second World War, Enigma was
the basis for many more sophisticated rotor cipher
machines like the Swiss NEMA, the American KL-7 ADONIS
and the until recently top secret Russian M-125 FIALKA.
Although Enigma was very well designed and offered, for
those days, an unbreakable security, the negligent use in
the German Armed Forces and the compromised codebook
material enabled the codebreakers to turn the best kept
secret of the war into a Trojan horse and give the
kick-off for cryptographic intelligence. Today, Signal
Intelligence is considered to be a most vital part of the
modern battle.
Paul Reuvers' and
Marc Simons' CryptoMuseum.com Paul and Marc host the Crypto Museum
website with an extensive Enigma section that
contains detailed information and many beautiful
images of many different Enigma machines.
Tom Perera's
Enigma museum Tom is a
collector of Enigmas and other cipher machines.
On his site, you can find a huge number of very
detailed photographs. He's also the first to
publish all details of the famous Russian Fialka
M-125, top secret until recently.
Tom's Enigma In
Action video Tom
created a very nice video that shows how to set
the daily key on the Enigma, change the rotors,
ring settings and plugboard connections, and how
a message is enciphered. Great way to see the
Enigma in action.
Frode Weierud's Crypto Pages As a member of the Crypto Simulation
Group, Frode has composed a large list of sims.
Several Enigma models, PURPLE, the SIGBA, Hagelin
CD57 and others. The site contains also a lot of
historical information and documents. CSG is
decoding a large number of original WW2 German
messages, some of which are already published on
Frode's site.
Breaking German
Navy Cyphers Michael
Hoerenberg's website about breaking authentieke
Enigma M4 messages, retrieved from salvaged U-534
Chiffriermaschine Patrick Hayes' pages about the Enigma
machine with many detailled photos of its parts
Tony Sale's Codes
& Ciphers Tony is
walking computer history. One of the people who
helped saving Bletchley Park. He even rebuilt the
famous Colossus computer in the Park's museum.
Bletchley Park Official site of the Bletchley Park
Thrust. In the Second World War, this was the
center of all British code breaking efforts.
Enigma on the
German U-Boats A great
site with a huge archive on the German U-boats.
There is a very interesting page on the use of
Enigma and the efforts on breaking the U-boat
Enigma codes
Enigma and the
Bombe The story of
breaking enigma and the use of Bombes by Graham
Ellsbury.
Enigma World Code
Group Bruce Culp's
excellent website, designed to join Enigma
enthousiasts and globally exchange Enigma
encrypted messages. Provides clear and simple
instructions on how to encrypt and decrypt
messages. Code books provided.
OPERATION TURING Mitchel Thomas and Indiana Popovich
made a website where you can decrypt enigma
messages (keys provided) to unveil the story of a
fascinating 1938 intelligence operation in a
shadowy pre-war atmosphere. More info about how
and why on my weblog
Enigma.edu.pl
Radoslaw Wesolowski's website, dedicated to
enigma.
The Enigma Machine An interactive exploration of the
encryption powers of the Enigma Machine by
engineering students at Olin College.
Jim Oram's Enigma
Replica Jim produced a
perfect replica of the real thing. Now, even
Enigma collectors order spare parts in his shop.
Great site!
Arduino Enigma
Simulator An
electronics project, based on the
ATmega168-microcontroller, simulating several
Enigma versions, with a small touch screen
interface. More information about the project is
published at the project weblog.
Enigma simulators
for RISC OS platform
Site with a range of Enigma simulators for
computers with the RISC platform. Paul Reuvers
from X-Ample Technology has created a list of
Enigma sims, the M3, M4, Luftwaffe en G312 Abwehr
Enigma.
Daniel Palloks
Javascript universal Enigma Excellent Javascript simulation of 12
different Enigma models, including the Abwehr G,
Kriegsmarine M3 and M4 and the additional use of
the Enigma Uhr.
Turing and U.S
Navy Bombe Simulator
including the Turing-Welchamn and U.S Navy Bombe,
Enigma M3, M4 and Checking Machine, by Magnus
Ekhall & Fredrik Hallenberg
This software is an exact simulation of the
3-rotor Wehrmacht and Luftwaffe Enigma, the 3-rotor
Kriegsmarine M3, also called Funkschlussel M, and the
famous 4-rotor Kriegmarine M4 Enigma cipher machine, used
during World War II from 1939 until 1945. You can select
between the three models, actually choose different
rotors or 'Walzen', preset the rotor wiring positions or
'Ringstellung' and switch letters by using plugs or
'Stecker'. The internal wiring of all rotors is identical
to those used by the Wehrmacht, Luftwaffe and
Kriegsmarine. This simulator is therefore fully
compatible with the real Enigma-machine and you can
decode original messages and make your own encoded text.
Runs under Windows.
In 1926, the commercial Enigma was purchased by
the German Navy and adapted for military use. They called
it Funkschlüssel C. Meanwhile, Chiffriermaschinen-AG
developed a special Enigma with rotors that have the same
contact alignment as the D rotors, but with teeth,
multiple notches and are advanced by cog wheels instead
of pawls and ratchets (see patent drawing left). It also
had a rotating reflector and a counter on its left. Only
one is know to exist today. This probably experimental
model, presented in 1928 but exceptionally only patented
in 1931, lead to the Enigma G. The Enigma G had different
rotors with a zigzag pin placement and the counter on its
right. Its rotors, which also had multiple notches, were
moved by a system of gears, similar to the 1928 special
predecessor. Already in 1928, the German Abwehr (Secret
Service) bought the 12 Kg light Enigma G, also called
Zahlwerk (clock-work) Enigma due to it's counter on the
front panel. The Enigma G was exclusively used by the
Abwehr.
Volume
2, "Notes on German High Level Cryptography
and Cryptanalysis".
This software is an exact simulation of the
3-rotor Wehrmacht and Luftwaffe Enigma, the 3-rotor
Kriegsmarine M3, also called Funkschlussel M, and the
famous 4-rotor Kriegmarine M4 Enigma cipher machine, used
during World War II from 1939 until 1945. You can select
between the three models, actually choose different
rotors or 'Walzen', preset the rotor wiring positions or
'Ringstellung' and switch letters by using plugs or
'Stecker'. The internal wiring of all rotors is identical
to those used by the Wehrmacht, Luftwaffe and
Kriegsmarine. This simulator is therefore fully
compatible with the real Enigma-machine and you can
decode original messages and make your own encoded text.
Runs under Windows.