The Anglo-Americans
were able to gain information of great value from reading their enemies secret
communications. In Britain the codebreakers of Bletchley Park solved several
enemy systems with the most important ones being the German Enigma
and Tunny cipher
machines and the Italian C-38m.
Codebreaking played a role in the Battle of the Atlantic, the North Africa
Campaign and the Normandy invasion. In the USA the Army and Navy
codebreakers solved many Japanese cryptosystems and used this advantage in
battle. The great victory at Midway would
probably not have been possible if the Americans had not solved the Japanese
Navy’s code.
However the
Axis codebreakers also
had their successes and they were also able to compromise various Allied crypto
system both low and high level.
One
interesting question that often comes up in history books is whether the
Germans ever suspected that their Enigma cipher machine was being read by the
Allies and how the war could have taken a different turn had they managed to
discover that it was not secure.
The truth is
that the Germans never considered the Enigma to be unbreakable and in fact they
had discovered in 1939 that the Poles had solved messages. During the war they
continued to investigate the Polish solution of the Enigma, which they called
case ‘Wicher’. (1)
The
plugboard Enigma and the German armed forces
The Germans adopted
a modified version of the commercial Enigma machine as their main cipher system
in the 1930’s. The modification they introduced in the commercial model was a
plugboard. This vastly improved the cipher security of the Enigma device.
In 1934 the
Army and Navy agreed to use the plugboard Enigma as their main cipher system
and in 1935 the Airforce followed (2). At the start of WWII Germany was the
only country in the world to use a cipher machine for all its mid and high
level traffic.
During WWII
tens of thousands of Enigma machines were used by the Germans. It seems that no
one knows for sure how many Enigma machines were built however a good estimate,
based on their serial numbers, is that more than 40.000 were constructed. (3)
The Germans
used the Enigma extensively and they were always worried about the security of
their main cipher system. Their cryptologic security departments, scattered
across their cryptologic agencies, researched ways to break the Enigma and
based on their observations changes were made in operating procedures. Although
it is often claimed that they considered the Enigma to be unbreakable the truth
is that they constantly upgraded
its security, both with physical modifications and with new, more secure cipher
procedures.
One of the
reasons that they improved the Enigma during the war was that they had learned
that in the prewar period the Polish codebreakers had been able to solve
messages.
The Polish
solution of the Enigma in the 1930’s
In the 1930’s
the rise of Hitler’s National Socialist
German Workers' Party led to German rearmament and a more aggressive
foreign policy. This change in policy alarmed European nations and especially
in neighboring Poland there was a great need to keep a close eye on the
military developments in Germany.
The Polish
state had limited resources but the intelligence service operated efficiently
and was able to gather valuable intelligence against the main Polish enemies
which were Nazi Germany and the Soviet Union. The Poles had a tradition in the
field of cryptanalysis as their codebreakers had contributed to the defeat of
Soviet troops in the war of 1919-1921
by solving the codes of the Red Army.
In the early 1930’s the Polish cipher bureau
concentrated on the solution of the widely used Enigma cipher machine and for
this reason hired three young mathematicians: Marian
Rejewski, Henryk Zygalski and Jerzy Różycki. Thanks to cipher material obtained through France
these codebreakers were able to solve the plugboard Enigma and read German
messages. In this task they succeeded where the French and British codebreakers
had failed!
German
indicator procedures and the ‘Grundstellung’
The Polish
solution was based on the German indicator procedure. Each Enigma network had
its own settings which changed monthly, up to October 1936 when they were
changed each day. The key list specified which rotors would be used and their
position in the scrambler unit, the ring settings on the rotors and the
plugboard settings. In addition the keylist specified the Grundstellung (basic setting) for the network. This was the position of the rotors
used to encipher the indicator of each message.
The indicator specified the starting position of the rotors which was
different for each message. The way the system worked was that the Enigma
operator had to set up the machine according to the instructions of the keylist
and then had to select a random starting position for the 3 rotors for each
message. This position was communicated to the other party after doubly enciphering it on the basic
setting.
So let’s imagine that a cipher clerk has set up his Enigma machine
according to the daily settings and is ready to encipher a message. He turns
the rotors of the machine at random and stops when they are at WJS, which will be his ‘message key’.
With the wheels at WJS he
starts typing out the message and the cipher text is written down by another
clerk. In order to send this message to another party he needs to add at the
beginning of the message the enciphered indicator so the operator who receives
it will know to set his machine rotors at WJS. The procedure used up to May 1937 (for the Navy) and
September 1938 (for the Army and Airforce) was to take the initial position of
the rotors for the message (in our case WJS)
and encipher it twice in succession at the Grundstellung/basic setting. So in our example the cipher clerk would have
to set the Enigma rotors to the network’s Grund setting, let’s say KJW and
type WJS twice. Let’s assume
that the output is HCE VKR. These 6
letters would be placed at the start of the message as the indicator. Then the
cipher clerk who received the message would turn his rotors to the Grund
setting KJW and type HCE VKR,
which would give him WJS WJS. Thus he would know that the message key is WJS
and he would be able to decipher the message.
The Polish codebreakers were able to exploit the use of a Grund setting
and the double encipherment of the message key. The flaw in this procedure was
that there was a connection between the first and fourth, second and fifth and
third and sixth letters of the indicator. It is obvious that these letters represented
the same initial letters of the message ‘key’ at three stages apart. Using mathematical theory the Polish
mathematicians were able to recover the Enigma settings and the messages keys
so they could decode the radio traffic.
However in the late 1930’s the Germans upgraded the security of the
Enigma by modifying their operator procedures. In May 1937 the Navy introduced
an indicator book and encipherment tables for the indicators thus defeating the
Polish method. In September 1938 the Army and Airforce abandoned the use of the
Grundstellung and each Enigma operator had to choose a random starting position
as the message key and encipher it twice at another random position. In our
example instead of KJW
the operator will choose another rotor position, let’s say JME and encipher the
message key WJS twice thus giving KDB CUJ.
The indicator sent with the message will be JME KDB CUJ. The receiving party will set their Enigma at JME and type KDB CUJ,
giving WJS WJS which will be indentified as the message key.
Although the German Army and Airforce abandoned the Grundstellung they
continued to encipher the message key twice thus allowing the Poles to
compromise this new procedure. However the Polish operation would finally end
in December 1938, when two more Enigma rotors were issued (making a total of 5),
as the Polish cipher bureau did not have the resources needed to overcome this
setback.
The greatest contribution of the Polish codebreakers to the Allied
cause came in July 1939 when their officials revealed to British and French
codebreakers that they had been solving the Enigma for years and shared their
method of attack. This breakthrough allowed the Franco-British alliance to
solve some Enigma traffic in the period 1939-1940 and made it possible for
Bletchley Park to avoid a costly and time consuming attack on the Enigma.
Der Fall
Wicher
In September
1939 Germany
invaded Poland and after a brief period of fighting was able to defeat its
armed forces and occupy the country. The Polish cipher burau was based in an area
south of Warsaw and was evacuated before the German troops arrived but it seems
that not all of their documents were properly disposed of. When the Germans
examined the area they were able to find documents pointing to a very secret
department in the cipher bureau, unusually large payments made to
mathematicians and translations of messages thought to have been sent on the
Enigma machine (4).
This
information obviously alarmed the German officials and during the war they made
efforts to locate and interrogate Polish officials that might know more about
the Enigma compromise. The German called this investigation case ‘Wicher’ (der fall Wicher).
Unfortunately
the information we have on their investigations is very limited and often
contradictory. The NSA article ‘Der Fall WICHER: German Knowledge of Polish Success on ENIGMA’ by Joseph A.
Meyer has a summary of the information from various TICOM reports but some of
the statements made are not correct. 
At the same time there are a few references to case ‘Wicher’ in the war diary of Inspectorate 7/VI but I haven’t been able to locate any actual reports. It should also be noted that the German cryptanalysts involved in these investigations were not interrogated after the war, so we do not have their side of the story.
German investigations and information from the War Diary of Inspectorate 7/VI
According to
‘Der Fall WICHER’ and various TICOM
reports (5) in 1939 the Germans were able to find incriminating evidence left
behind by the Polish codebreakers when they evacuated their headquarters. It seems that the plaintext versions of a few
Enigma messages were found thus showing the compromise of the cipher machine.
Unfortunately I don’t have the 1939 and 1940 reports of the German Army’s
codebreaking agency Inspectorate 7/VI, so I can’t say whether more information
can be found there.
In any case the Germans after researching the security of the indicator
procedure seem to have discovered on their own that the double encipherment of
the indicator was a risk and in May 1940 it was changed. From then on
the cipher clerk chose a random message key and enciphered it on another random
setting only once. In our previous example this means that instead of
sending the indicator JME
KDB CUJ, only JME KDB would be sent.
Since the Polish solution was based on the double
encipherment of the indicator this change defeated their method. From then on
the codebreakers of Bletchley Park had to employ their own method of solution
which was based on the use of ‘cribs’ (suspected plaintext in the ciphertext) and high-speed cryptanalytic
equipment called ‘bombes’.
However there is no indication that this indicator change was implemented
due to the ‘Wicher’ case. A German Army cryptanalyst named Buggisch said in
TICOM report I-92 ‘Final Interrogation of
Wachtmeister Otto Buggisch (OKH/In 7/VI
and OKW/Chi)’, p5
that the change came as a result of standard security studies:
The war diary of Inspectorate 7/VI, in the report of February 1942, says that an investigation of captured Polish files revealed deciphered German radio messages and this material was forwarded to Inspectorate 7/VI to clarify if the compromise was a result of treason or deciphering and if it was the latter to identify the compromised cipher system.
During the war representatives from the German cipher departments and the military intelligence service Abwehr had meetings on case ‘Wicher’. Although ‘Der Fall WICHER’ says in page 9 that the Naval High Command – OKM did not know about the Polish affair the war diary of Inspectorate 7/VI for the month of April 1942 shows that a meeting took place between the Naval officers Stummel and Singer, the Abwehr officials Dr Schneider and a captain and the Army cryptanalyst Dr Pietsch.
Another
reference to case ‘Wicher’ can be found in July 1942 when the aforementioned Dr
Schneider together with the department head of Inspectorate 7/VI visited imprisoned
Polish intelligence officers who had served in the General Staff. The report says that the results were meager
as some of those that the police had arrested were the wrong people and those
that were interrogated either did not volunteer information or had such a low
position that they did not know anything of value. The only admission made by
the Poles was that they had solved the hand cipher used by the German Army and
Police.
The only other reference I’ve found is in September 1943 when Dr Schneider, the OKM’s Captain Singer and Inspectorate’s 7/VI Dr Pietsch visited the Neuengamme concentration camp (near Hamburg) and interrogated the Polish intelligence officer Leja. A report was issued but I’m afraid I don’t have it.
After the fall of Poland a few Polish codebreakers were able to reach France and started working for the French signals intelligence organization (codenamed PC Bruno), commanded by Gustave Bertrand. After 1940 this unit changed name (codename Cadix) and location and continued to monitor and decode some German communications, including a few Enigma keys (6). ‘Der Fall WICHER’ says in page 5 that ‘The French cryptanalyst Bertrand was arrested and interrogated at this time, but he did not disclose the ENIGMA work, and it is very likely that he did not know what was happening in England and America on the problem’. This might not be entirely accurate as ‘the book Enigma: The Battle for the Code’, p319 says that in January 1944 ‘Gustave Bertrand is arrested by the Germans while working under cover for the Resistance in France. He admits to himself that he will not be able to remain silent if he is tortured, so, in order to obtain the chance to escape, he agrees to collaborate with the Nazis‘.
The same source, ‘Enigma: The Battle for the Code’, p319 says that in
March ’44 the Polish officers ‘Gwido
Langer and Maksymilian Ciezki confess to the Germans that the Enigma cipher was
broken before the war’. However there is no reference to this event in the
war diary of Inspectorate 7/VI, at least in the files I have.
Unanswered
questions
From the
information presented so far it is clear that in 1939 the Germans were able to
find proof that their Enigma cipher machine had been read by the Poles. However
it doesn’t seem like they were able to conclusively identify the Polish methods
of solution. In any case they correctly dropped the double encipherment of the
indicator in 1940, thus defeating the main Polish method of solution. During
the war they continued to investigate case ‘Wicher’ but unfortunately we do not
know what kind of information they got from interrogating the Polish officers. Buggisch said in TICOM report I-92, p5 that
when Dr Pietsch (head of the mathematical research department of Inspectorate
7/VI) interrogated the two Polish officers in 1944 ‘he did not bother to get the details of the Polish method’. This
seems nonsensical and it’s possible that Buggisch either did not know more on
the subject or was trying to mislead his interrogators.
In any case the people they interrogated could not have told them what
they really needed to know, mainly that the British codebreakers could solve
daily keys through the use of ‘cribs’ and high speed cryptanalytic equipment.
The Germans certainly did not think that the Enigma was unbreakable and
they continuously upgraded its security from the 1930’s till the end of the war
(7). Regarding their investigations on the theoretical solution of the machine
so far we know that the Army codebreakers wrote several reports on how the
internal settings could be retrieved under different sets of circumstances (8).
In 1944 the naval cryptanalyst Frowein showed that the 4-rotor Enigma could be
solved on a crib of 25 letters (9).
Unfortunately
with different agencies investigating the security of the Enigma and with their
reports scattered across different government archives it is difficult to reach
a conclusion regarding their investigations. It is up to researchers to locate
and study the relevant reports so a conclusion can be reached regarding the
German knowledge of possible solution methods for the Enigma.
Notes:
(1). Der Fall WICHER: German Knowledge of Polish Success on ENIGMA
(2).
‘Decrypted Secrets Methods and Maxims of Cryptology’, p118
(3) The Journal of Intelligence History article:
‘The Admiralty And Cipher Machines During The Second World War: Not So Stupid
After All’, p3
(4). Der Fall WICHER: German Knowledge of Polish
Success on ENIGMA, p3-4
(5). TICOM
reports I-78, I-92, I-127, I-200
(6). Intelligence
and National Security article: ‘Signals
intelligence and Vichy France, 1940-44: Intelligence in defeat ‘, p184: ‘According to Bertrand, between October 1940
and November 1942, 'Cadix' decoded 673 Wehrmacht and 3,097 police and SS
transmissions pertaining to France and occupied Europe. Bertrand subdivides
these decrypts into Wehrmacht Enigma transmissions, police and SS messages,
Abwehr agents' instructions and reports, and Armistice Commission signals
encoded manually.’
(7). Enigma
security measures
(8). TICOM
DF-190 series reports
(9). TICOM I-38
‘Report
on interrogation of Lt. Frowein of OKM/4 SKL/III, on his work on the security
of the German naval four-wheel Enigma’
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