(the previous nodes pay some closer attention to how the Enigma works)
The Enigma is a machine that looks like a typewriter. It is an electronic
device that has three cipher wheels in it. When the operator sets the
wheels and presses an "A" on the Enigma, a bulb marked with the
letter "T" might light up on a board. The letters that are keyed
in are not transmitted - instead, the "converted" text is sent
via morse.
When pressing a key on the keyboard, electric current would move via the
three cipher wheels and scrambling circuitry. The Enigma had to be set up
by turning the wheels to an agreed setting, and by plugging connectors into
specific sockets.
So far, there hasn't been much encryption going on. Here is where the fun
begins; the right wheel revolved counter-clockwise a twentysixth of a revolution
(i.e one letter) every time a key was pressed. This means that writing the
string "AAAA" might come out as "FEYW". Not only this,
but there was a complicated system of the wheels turning. When the right wheel
had made a full revolution, for example, one of the other wheels would turn
one notch. Scientists have calculated that if using the Enigma as a regular
typewriter (i.e without changing the settings underways) - there would be
in excess of 17.000 keystrokes between every time the wheels being back
in their original position.
Inside the Enigma, there were three (four, in the Shark Naval enigma
towards the end of the wars) wheels with 26 pins in each. These pins would
connect with the next wheel or the "switchboard" at the end of the
current.
Each of these wheels contained 26 wires, so that if the current could take
the following route:
- Operator presses A
- Wheel 1: A -> T
- Wheel 2: B -> W
- Wheel 3: Q -> B
- Switchboard E -> Q (also called reflector)
- Wheel 3: T -> R
- Wheel 2: N -> P
- Wheel 1: L -> Y
- Light: Y
For a closer look on how all of this works, read how to make an enigma
Breaking codes today might seem boring, if not trivial to most of us.
In wartime, however, the situation is very much different. In wartime, positions
of submarines, battle ships and aeroplanes is crucial. Also, most invations
and attacks don't happen spontaneously - they are all carefully planned.
this is where radio and Morse code comes in.
An old saying says "Keep your friends close and your enemies closer".
This is not without reason - knowing what your enemy is going to do before
they are going to do it might win you a war. This is what the Enigma cipher
was all about. From before the war even started and all the way until D-day,
when allied forces set foot on Normandie in France, the Enigma cipher
was a constant battle.
The breaking of the Enigma cipher has saved the lives of thousands and thousands
of allied sailors, and the fact that the allied forces often knew where
the German submarine packs would hang around, meant that the tanks, artillery
and other weapons coming across the Atlantic from USA and other countries
reached their destinations.
Before the war
In 1931, Hans Thilo Schmidt, brother of a high ranked German army official,
and trusted employee of the german cipher office, sells information about
the Enigma to french secret service - manuals on how to operate it and the
current settings of the machine. The information was sold to the French
secret service, who were extatic about this breaktrhough.
Between 1931 and '38, more and more documents about the Enigma were leaking
from the cipher office. However, the non-technical documents and current
settings of the cipher machine were not believed to be able to help crack
the code.
When rumours about the plans of invations by the Germans started moving,
several instances started work on trying to break the Enigma codes. A team
of Polish cryptographers, led by dr Antoni Palluth, were on the task
from 1932.
The German Mistake
When sending a message, the Germans decide d to send the settings twice,
before sending the actual message. If you know anything about cryptography,
you know that was a big mistake;
Sending the settings would be done in a predetermined setting, say "BLT".
If the message would be transmitted on in the wheel settings of "QWE",
the operator sending the message would first set his machine to BLT, and
then type QWE twice. The result would be something like "RHU TFP".
When the receiver gets the RHU TFP message, all he would have to do is to
is to set their machine to BLT and then type RHU TFP. The bulbs lighting
up would then be "QWE QWE".
The receiver would then set his Enigma machine to the QWE setting, and
decode the rest of the message.
The problem with this, of course, is that when the Britons found out
that the first 6 characters of the message would be the same sequence repeated
twice, this helped them in their quest. Because the manuals had been captured,
the fact that the current went through the machine twice, and that the codebreakers
knew that the characters were in the pattern "ABC ABC", led them
to discover ways to interpret the first 6 characters. Doing this, they
could decipher messages relatively fast - usually within 48 hours.
This procedure was changed in 1938 (random letters were sent before
the actual message and acknowledgement) but the practice of sending the
cipher settings twice continued - allowing the code to be broken again,
except it now took some more time.
The second world war
As the second world war broke out, the Germans started making more code
wheels. There were still just three wheels in use, but now a total of five
wheels were available. Also, considering that each wheel could be placed
in any position in the machine, and each wheel had 26 possible positions,
you now had a machine with (5*4*3*26^3)
It was not until December 1939 that the Enigma messages could start to
be decoded.
Earlier, the codebreakers had discovered that there was a certain pattern
to the messages, and devised a system of perforated sheets of paper. A certain
result from the first six characters of the message ruled out a load of
options - another result ruled out even more etc. The problem, of course,
was that the sheet system only worked for a particular set of wirings. If
a different order of wheels was used, the sheets were useless. In the beginning
there were just three wheels, making 6 different possibilities when it came
to wheel order (3*2*1) Later in the war, possibly when the Germans realized
that the code had weaknesses, two extra wheels were introduced. Because
there were 60 possible combinations now (5*4*3), the codebreakers would
need 60 sets of sheets. This was not a good solution, and a new way to break
the codes had to be found.
In mid-January 1940, the first "genuine" wartime message
was decoded.
Historic points in the breaking of the Enigma code
Alan Turing is the man who has become most famous for the breaking of
the Enigma. The first important thing he made was the Bombe. This was
an electronic device that had several Enigma machines wired together.
The purpose of this was to rule out combinations of wheels and positions,
much like the sheet system, only more automated. This original idea was
later improved a number of times, and it is believed that this invention
is what made the decryption possible at all.
The Navy Enigma was different from the other two, as the Germans felt
that the war on sea was the most important to begin with. Indeed, the German
wolfpacks (submarines) were a major danger to ships in the Atlantic
and North Sea. This was also why the codebreakers tried hardest to break
the Naval Enigma. The first time the Naval enigma was actually broken was
on April 25th 1940. Unfortunately, the Germans kept changing their codes,
and every time a code was changed, the work with breaking the Enigma started
over.
The British codebreakers had a lucky break when they discovered a severe
weakness in the German coding procedures: When sending weather forecasts
around, the Luftwaffe Enigma was used. However, there was a consistency
in how the messages were sent; They always begun with something like "Station
Oslo reporting". Knowing this, the Brits could automate the tasks
of breaking the codes by using the Bombe, and by looking for the message
"Station (...) reporting". Because the breakers would usually
know where the messages came from, breaking the code became a fairly easy
routine task.
From August to October in 1940, the codebreakers couldn't decipher
one single naval Enigma message, as there had been a slight change in
procedure, making the decoding more difficult.
In May of 1941, Allied ships managed to capture the German submarine
U-110. This marked a major breakthrough, as it was the first time the
codebreakers had their hands on an original submarine Naval Enigma machine,
and copies of all the codebooks that were needed.
From July of 1941 all the Naval Enigma messages were broken. Some of them
took a litttle longer than others (up to a week) but most of them were broken
within 48 hours. When the code was broken, the codebreakers could quickly
decrypt the remainder of the messages for the 48 hour period, until the
codes would once again be changed.
In 1942, something bad happened - The Naval Enigma was suddenly unbreakable
again; The original Naval Enigma had been switched with what the Germans
called the Triton Enigma (the codebreakers at Bletchley called it the Shark
Enigma). This was the same as the original enigma, but with another wheel
added to it. Fortunately, this wheel was fixed in the machine and did not
add up to the total number of wheel orders. On the other hand, this did
multiply the number of possible ciphers with 26 - making the use of the
Bombe more time consuming.
The base of this writeup is the book Enigma: The Battle for the Code
written by Hugh Sebag-Montefiorte. If you are interested in reading an engaging,
well written and seemingly complete account of what went on when the Enigma
was broken, this would be the book.
Other sources include a selection of sources from the internet and history
books (particularily Seizing the Enigma, by David Kahn, as well as the
play Breaking the Code, written by Hugh Whitmore.
There is really no way to tell the whole story about the Enigma without doing
a lengthy study on the topic. This writeup becomes a mere shadow of the complexity
and excitement, but I believe it makes a good overview of what went on and
why.