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.
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 which
was used by the German Reichsbahn in Eastern Europe, was
partially broken from 1941 onwards.
Military versions
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. Today, only one such machine
is known. 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 rewireable 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, introduced 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 codebooks 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 known 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 settings. 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 analyze and break the Enigma
messages. Although the chief of this Bureau
received copies of key sheets, 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 cryptanalysis. Two major
security flaws in the German Enigma procedures
were the global ground setting and the twice
encrypted 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 keys due to increased
sophistication in the design, new procedures and
lack of funds for the codebreakers. 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
a codebook 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 and ciphers,
was codenamed ULTRA and played a very important
and often decisive role during the war, mainly in
the Battle of the Atlantic. The 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
coordinated 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 ciphers 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 TRITON key and its procedure
(called SHARK by the codebreakers) 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 messages 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 Bletchley
Park discovered by cryptanalysis that a fourth
rotor had entered the battlefield. After ten
nerve-wracking months of heavy losses, Bletchley
Park succeeded in breaking the TRITON keys. 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.
German operators were also
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 defenses, 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 NSA's Axis SIGINT). More about the
mathematical security of the Enigma is found in the Technical
Details page.
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.
More related to Enigma (offsite -
opens in new tab)
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 authentic
Enigma M4 messages, retrieved from salvaged U-534
Chiffriermaschine Patrick Hayes' pages about the Enigma
machine with many detailed 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
enthusiasts and globally exchange Enigma
encrypted messages. Provides clear and simple
instructions on how to encrypt and decrypt
messages. codebooks 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
The Enigma Machine An interactive exploration of the
encryption powers of the Enigma Machine by
engineering students at Olin College.
Enigma Replicas and Simulations
(offsite - opens in new tab)
* Virtual 3D Enigma
by Martin Gillow is a
fully functional 3D model of the Enigma I, M3 and
M4 that runs in your browser. The simulation has
a Tutorial and can run in Tutorial Mode. There
are also simulations of the Colossus, Lorenz
SZ40/42, Typex, Dragon, Ernie and ICT 1301
Flossie.
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 and 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. This sim also shows the signal
path (use "Show monitor" button).
Turing and U.S
Navy Bombe Simulator
including the Turing-Welchman 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
decrypt original messages and make your own encrypted
text. Runs under Windows.
). More about the
mathematical security of the Enigma is found in the Technical
Details page.
Volume 2, "Notes on German High
Level Cryptography and Cryptanalysis".