General
Gamelin who commanded the French forces told Churchill that the defeat was due
to: ‘Inferiority of numbers, inferiority of equipment, inferiority of method’.
In fact both sides had roughly similar strength in troops and aircraft while in
tanks it was the Franco-British alliance that had the advantage, both in terms
of numbers and of quality.
However the
German were able to overcome their tank inferiority by grouping their armored
divisions together, supporting them with ample airpower and providing them with
dedicated infantry, anti-tank, artillery and communication units. At the same
time their radio communications system was much more advanced than the French
Army’s and orders could be dispatched quickly and securely to all units.
The German
leadership also took a big risk by attacking
through the Ardennes area with the purpose of cutting off the northern part
of the Allied front.
Another area
where the Germans had the advantage was in signals
intelligence. Unfortunately historians have focused almost exclusively on
the German Enigma
cipher machine and its solution by the codebreakers of Bletchley Park thus
neglecting the many
successes of the German codebreakers.
The German
victories during the period 1939-1942 in France, N.Africa, Atlantic and in the
Eastern Front were achieved at least in part thanks to their ability to read
their enemies communications.
French
military codes and the Battle of France
The French
military and civilian authorities used for their secret communications several codebooks,
both enciphered and unenciphered. Individually these systems did not have a
very high degree of security but it seems that the French strategy was to
overwhelm enemy codebreakers through the simultaneous use of a large number of
different codebooks (1). Additionally, it is possible
that the French Army’s cipher bureau overestimated the security of the
encipherment procedures used with the codebooks.
According to
the available sources the following cryptosystems were in use in 1939 (2):
For high level
networks (Army High Command and Army Corps) the machine cipher B-211 and
5-figure/5-letter dictionaries enciphered with transposition methods.
For mid level
networks (Armies and Divisions) the machine cipher C-36 and the 4-figure/4-letter codebooks RA,
ATM and 69.
For low level
networks (small Army units like battalions and regiments) codebooks enciphered
with short additive keys (9-13 digits long) plus 3-letter dictionaries.
From recently
released TICOM reports and various books it is clear that the Germans could
read French Army tactical codes (3), the Navy’s main cipher system (4) and the
Airforce’s ‘Aviation Militaire’ (5). By exploiting these systems the Germans
obviously got valuable intelligence. However their main success that directly
contributed to their victory in 1940 was achieved against high level
enciphered codes used by the French War Ministry.
The code of the French War Ministry
From the early
1930’s the German codebreakers could read the code used between the French War
Ministry and the various military districts. This was a 4-figure codebook of
10.000 values enciphered with additive sequences. In September 1939 there was a
change in the method of encipherment and columnar transposition was used
instead of addition. Unfortunately for the French this method had been used by
one of their military districts prior to September 1939, thus allowing the
Germans to solve it and figure out how the transposition keys were chosen. Thanks
to this compromise the Germans could read messages of the War Ministry and the
military districts till June 1940. The information gained concerned the French
army’s order of battle, the weak point of the Maginot Line, the mood of the
troops and the population in France and in the colonies, the order of battle of
the British troops stationed on the mainland and their movements.
Information
on the compromise of the FLD code is available from several sources.
Colonel
Mettig, head of the German Army’s signal intelligence agency Inspectorate 7/VI
in the period 1941-43, said in TICOM report I-128 ‘Deciphering
Achievements of In 7/VI and OKW/Chi’,
p2
‘In assessing the value of Signals Intelligence
PW considers that the deciphering of messages of strategic importance is more
valuable than deciphering those of tactical importance. He therefore rates most
highly the solution of the French ciphers in the FLD military network radiating
from Paris. The deciphering of this traffic before and during the war gave a
clear picture of the order of battle of the French and Belgian armies and also
of the British army.’
This success was accomplished by the codebreakers of the German High Command's deciphering department – OKW/Chi. Wilhelm Fenner, who was head of the cryptanalysis department of OKW/Chi, said in TICOM DF-187B, p7
‘Even
before the military action with France began, the military systems of French
higher staffs were solved. This was a 4 or 5-figure code that was
systematically transposed (tableau carve) .In the cryptograms a few parallel
passages (repetitions) were discovered .The interval between these passages was
constant and must therefore correspond to the width of the transposition box as
cryptanalytic studies have shown.If I am not mistaken the keys (Loesungen
? ? ? ) ? ? the box itself were taken from the same code
book. Despite all the cunning of this cryptographic system, the occurrence of
short parallel passages proved fatal. By the aid of these deciphered
messages tabs could be kept on the French Army far back into the homeland.’
Colonel
Randewig, head of the intercept organization in the West during the 1940 campaign
wrote in the report FMS P-038 ‘German
radio intelligence’:
‘As early as December 1939 the Germans broke
a special cryptographic system used by the French command in radio messages to
the armies and military district headquarters. It had been used contrary to
regulations prior to the opening of hostilities in September 1939. The Germans
were able to solve this system because the radio station guilty of the violation
was reprimanded and thereupon repeated the same messages in the proper system.
Their contents revealed a certain amount of organizational information, for
example, the fact that the French 2d and 3d Cavalry Divisions had been
reorganized into the 1st and 2d Armored Divisions and were due to move into
their assembly area northeast of Paris by 1 January 1940. However, this type of
incomplete information could generally be considered only as a supplement to
and confirmation of other intelligence concerning the enemy. It was not
possible to deduce the enemy's order of battle from radio intelligence alone.
Nevertheless, the Germans could
identify the probable concentration areas of the French and British armies from
the practice messages sent by the field radio stations, although the boundaries
of army groups, armies, corps and divisions could not be established with any
certainty. Greater clarity prevailed about the fortified area behind the
Maginot Line in the south. Enemy forces stationed near the Frenco-Swiss and
Franco-Italian borders were not observed according to any regular plan.
Spot-check intercepting failed to pick up the French Tenth Army in the place
where it was presumed to be by the German command. However, radio intelligence
did indicate the presence of the French Sixth Army.’
The
importance of this intelligence is even admitted by the official history ‘British Intelligence in the Second World War
volume 1’, p163-4
‘It later became clear that, until
the fall of France, Germany enjoyed not only the strategic initiative but also
the advantage of good operational intelligence………. During the planning and the carrying out of the attack on France the work
of the enemy intelligence department of the General Staff of the German Army
was of crucial importance and its value fully justified the prestige which the
department had always enjoyed. The work has been described by General Ulrich
Liss, head of the department from 1937 to 1943. He emphasizes that partly on
the basis of British army documents captured in Norway, which provided all it
needed to know about the British order of battle, and partly from the cypher
traffic between the French War Ministry and the army groups, armies and home
authorities, most of which it read from soon after the outbreak of war until 10
May, the department had a very comprehensive and accurate knowledge of the
dispositions and qualities of the Allied forces………… During the campaign its intelligence continued to be good, and Sigint
continued to be the best source.’
However the person who can give the most accurate account of the work done
on the FLD code was the chief cryptanalyst of OKW/Chi, Erich Hüttenhain. According to Hüttenhain’s
manuscript ‘Einzeldarstellungen aus dem Gebiet der Kryptologie‘,
p14-16 (6) the code used between the French
War Ministry and the military districts was a 4-figure codebook of 10.000 values,
enciphered with short additive sequences. Since this method of encipherment
offered limited security and the underlying code remained in use for years
these messages could be read by the Germans. However a different system was
used by the military district in the border with Italy. Here the code was
transposed based on codewords. After finding two messages with parallel
passages the German codebreakers were able to solve this system in 1938 and they
realized that the transposition keys were created by using the codegroups of the codebook.
Thus from mid 1939 the traffic of this military district could also be solved.
In September 1939 when WWII broke out the French War Ministry instead of changing
the cipher procedures, ordered that this system of transposition was to be used
by all the military districts. Since the 4-figure codebook remained in use the
Germans could read this traffic up to June 1940 and Hüttenhain says that the German leadership was informed
of all significant operations within the French armed forces.Among his conclusions about this case were that a country should not adopt for its main cipher a system that is already known to the enemy and thus possibly compromised and that indicator groups should be independent of the cipher.
’Das
französische fld-Netz
Beim Anfang der
dreißiger Jahre benutzte das französische Kriegsministerium im Verkehr mit den
französischen Wehrkreisen zur Verschlüsselung der Nachrichten einen 4Z-Code,
der mit einer endlichen Additionszahl überschlüsselt wurde. Fast
alle 10.000 Gruppen des 4Z-Codes waren belegt. Der Code wurde im Laufe der
Jahre nicht geändert oder gar abgelöst. Die Additionszahlen wurden in kürzeren
Zeitabschnitten abgelöst. Es waren jeweils gleichzeitig mehrere Additionszahlen
im Gebrauch. Die Längen der einzelnen Additionszahlen waren ungerade und
schwankten zwischen 7 und 13 Ziffern. Die mit dieser Geheimschrift,also mit dem
4Z-Code verschlüsselten Nachrichten wurden in den letzten Jahren vor dem 2.
Weltkrieg vollständig mitgelesen. In dem Verkehr mit dem an Italien angrenzenden
französischen Wehrkreis verwendete das französische Kriegsminister rium ein
anderes Chi-Verfahren. Im vorangehenden Studium des gesamten Spruchmaterials
dieses einen Verkehrskreises wurden 2 Sprüche gefunden, die eine größere Anzahl
von fast gleich langen und über die ganzen Spruchlängen fast gleichförmig
verteilten Ziffernfolgen enthielten; lediglich die Reihenfolge der diese 2
Anfangszeilen bildenden Ziffernfolgen in den beiden Sprüchen war verschieden.
Diese Feststellung führte zur Erkenntnis, daß ein Ersatzverfahren mit einem
Würfel überschlüsselt wurde. Mit Hilfe von 2 Anfangsreihen konnte die
Würfellosung rekonstruiert und das Ersatzverfahren als 4Z-Code erkannt
werden.-Es war also in den beiden Sprüchen, die zum Einbruch in das Verfahren führten,
eine längere, sich über mehrere Zeilen des Würfelkastens erstreckende gleiche
Textstelle vorhanden.
Der 1. Einbruch gelang im Jahre 1938.
Im Laufe der nächsten Monate wurden weitere dieser Parallelstellen-Kompromisse
gefunden. Es wurden die in Wortlosungen umgewandelten Würfellosungen als die
Klarbedeutungen der Codegruppen des verwendeten 4Z -Codes erkannt. Und es wurde
erkannt, da als Kenngruppen für die Würfellosungen 4Z -Gruppen des Codes
gewählt wurden, deren Klarbedeutung jeweils die Wortlosung des Würfels war. Auf
diese Weise lieferten gedeutete Codegruppen neue Würfellosungen und
rekonstruierte Würfellosungen neue Codegruppen. Mitte 1939 wurde der gesamte
Verkehr zwischen dem französischen Kriegsministerium und dem an Italien
angrenzenden Wehrkreis, der also mit der Geheimschrift 4ZCüW verschlüsselt
wurde, mitgelesen.
Als am 3. September der Krieg mit
Frankreich ausbrach, verfügte das französische Kriegsministerium, daß die
bisher nur im Verkehr mit dem an Italien angrenzenden Wehrkreis benutzte
Geheimschrift 4ZCüW unverzüglich auch in allen anderen Wehrkreisen verwendet
wurde. Es blieb der Code derselbe, und es wurden die Würfellosungen nach wie
vor aus den Klartextbedeutungen der Codegruppen genommen. Es wurden lediglich
an den jeweils folgerden Monatsersten geringfügige Änderungen an den
Kenngruppen vorgenommen, Änderungen, die in kurzer Zeit erkannt und nach
einigen Wechseln sogar vorausgeahnt wurden.
Dieser Zustand blieb bis zum Ende des
Frankreichfeldzuges im Juni 1940 unverändert bestehen. Jeder aufgenommene
Spruch dieses militärischen Führungsnetztes, das als fld-Netz bekannt war,
wurde mitgelesen. Die deutsche militärische Führung war über alle wesentliche
Vorgänge innerhalb der französischen Wehrmacht unterrichtet. Neben der Gliederung
in der französischen Wehrmacht klärten die mit gelesenen Sprüche die Bewaffnung
der einzelnen Einheiten auf, die schwächste Stelle der Maginot-Linie, die
Stimmung der Truppe und der Bevölkerung in Frankreich und in den Kolonien, die
auf dem Festland stationierten englischen Truppen und deren Bewegungen usw.
Es erscheint angebracht, an Hand
dieses für Frankreich und für Deutschland folgenreichen Entzifferungs
ergebnisses einige Folgerungen zu ziehen:
1. Es ist falsch, ein
Chiffrierverfahren, dessen Sicherheit nicht bewiesen ist, zum Hauptverfahren zu
machen, wenn es bereits als Nebenverfahren als beim Gegner bekannt
vorausgesetzt werden muß.
2. Ein Chiffrierverfahren, dessen
Sicherheit von der Struktur der Klartexte-Anfängen, Schlüssen, Parallelstellen, Spruchlängen u.a. - abhängig
ist darf nicht verwendet werden.
3 Kenngruppen müssen vom
Chiffrierverfahren unabhängig sein; sie dürfen keine doppelte Bedeutung haben.
4. Die Erfassung des Spruchmaterials
sollte vollständig sein, um auch die kompromittierenden Sprüche finden zu
können.
Anm.: Rekonstruierte Seite einer
Kopie, deren 12 Anschläge links unlesbar waren. Hier sind also die ersten 12
Anschläge erraten,-allerdings sinngemäß! Ausnahme: Zeile 12, wo die Zahl 13
willkürlich ist,für die allerdings 2 Bedingungen stehen: 1) >7 und
Zweistelligkeit (in den 12 Anschlägen).’
Identifying
the FLD codes
We can try to
identify the cryptosystems used in the FLD radio network by looking at
Huettehnain’s statements and various TICOM documents.
According to
Army cryptanalyst dr Buggisch (7) the designations F90 and F110 referred to
French Army ciphers, read during the period 1939-1940:
‘F90 and
F110 were German designations for French Army cipher systems before and during
the campaign in FRANCE. Both were based on a four figure code, in one case the
recipher consisted of a periodic adder [or subtractor] of length 11; in the
other it was ordinary transposition, the transposition key being obtained from
a key word which itself was taken from the code and shown by an indicator
group. Both systems were being read from the winter of 39/40 to the end of the
French campaign. Solution was by methods generally known in cryptanalytic
circles. One of the codes turned, up again for a short period in De Gaullist
traffic.’
Note that
Buggisch’s description of the systems is similar to Huettenhain’s from ‘Einzeldarstellungen
aus dem Gebiet der Kryptologie‘.
In the TICOM
collection of the German Foreign Ministry’s Political Archive there are
documents that have more information on the ciphers F90 and F110:
1). The TICOM
documents T3611 and T3612 (8) have information on cipher F90, however document
T3611 is not available due to deterioration.
According to document
T3612 the cipher F90 was a 4-figure code enciphered with short additive
sequences of 5, 7 or 11 digit length.
It seems that the codebook consisted of 20 pages, each with 100 entries, totaling
2.000 code groups.
This system was
used by the network FLD (Paris) in communications with stations fla, flb, flc, flf,
flg, fak, fam, flq and others and it was solved thanks to a major cipher clerk
error committed in September 1937.
It seems that
the same message was sent twice, first without encipherment (so only the code
groups were transmitted) and then with additive encipherment. Clearly this gave
the German codebreakers an opportunity to identify the basic code groups and
then solve the additive sequence used for encipherment. This success allowed
them to correct their own relative code findings (from previous decipherments) into
the actual French code values.
The information
in TICOM document T3612 matches Huettenhain’s statements about a high level
code enciphered with short additive sequences being solved completely in the
years prior to WWII.
2). The TICOM document
T3684 (9) describes system F110 (F4ZCW110 - French 4-figure code with simple
transposition) and it says than from February 1938 the radio network of the
French 14th Army, with stations in Lyon, Grenoble, Modane, Briancon,
Chambery, Jausiers and Beurg-Saint-Maurice, started using this transposed code.
The indicator was 55555 and the transposition key was created from the plain
meaning of one of the codegroups. The example given in the report was:
p e r m i s s i o n o n n a i r e
13 2 14 7 4 16 17 5 11 8 12 9
10 1 6 15 3
The details in
the report match Huettenhain’s statements about a French military district adjacent
to Italy using a transposed code, with the transposition keys being created
from the codegroups of the codebook and the first breakthrough coming in 1938.
The
successors to systems F90 and F110
From the
available TICOM documents it seems that in September 1939 both systems were
changed. Cipher F90 was replaced by a new 3-figure code plus additive, while
cipher F110’s successor used the same underlying code but with a new
encipherment procedure.
1). TICOM
document T3661 (10) contains a report by the cryptanalyst dr Ludwig Föppl,
dated 18 December 1939. In the report Föppl says that the code F90, which was
used in the military command radio network FLD (Paris), was changed in
September and replaced by a new system.
The new system
was a 3-figure code enciphered by additive sequences. It seems the encipherment
consisted of a 20-digit number that was composed of two 10-digits parts. A
peculiarity of the encipherment was that each 10-digit number was composed of
all the ten digits from 0 to 9 used only once (11). This system was solved and
it seems that the German designation for it was F135.
2). In the
notes of dr Huettenhain there is a report from November 1939 that describes the
solution of the successor to system F110 (12):
'Report
on the attachment to Army Group C evaluation section
On 2
September 1939 the French Army Code F110 was replaced by a new code so that
traffic could no longer be broken currently.
On 3
September 1939 I was seconded to FRANKFURT-ON-MAIN in order to take part in the
task of breaking this new code. The task was accomplished at the beginning of
October so that all the September material could be read retrospectively.
This success
was made possible in such a short time by the fact that
1) the
necessary data (Code etc) was obtained by months of work in peace time, chiefly
by Herrn TRAPPE (Chi OKW) and SCHMIDT (Chi OKW)
2) a close
co-operation between the above named gentlemen and me could be established.
It was
therefore, still possible in October to work on the October material with
success. In addition to the above named gentlemen Herr Professor Dr. FOPPL was
of great assistance in the solution of this system.
As the
system was not changed on 1 November 1939 this code could be read currently
again from the date when the October key was broken. On 3 November 1939 at the
finish of my attachment in FRANKFURT-0N-MAIN I was sent to BERLIN.’
From
Huettenhain’s report it seems that the underlying code remained the same (as in
system F110) but the encipherment procedure was changed. By having the code the
German codebreakers only needed to attack the encipherment and this was quickly
achieved according to Huettenhain.
Conclusion
Conclusion
The German
victory in the Battle of France shook the world in 1940 and countless theories
were formed in order to explain this unusual event. Up to 1940 the French Army
was thought to be the most powerful and best equipped force in Europe. Supported
by the small British
Expeditionary Force, the powerful British Fleet and with military supplies
coming in from the United States the Franco-British alliance had every reason
to expect a victory over Germany thanks to its superior economic resources.
The German
leadership took a huge gamble by concentrating all their armored divisions and
using them to encircle and destroy the northern flank of the Allies but this
gamble paid off. In a victory of such magnitude it is not possible to attribute
success to only one factor. Obviously the German advantages in training,
doctrine, leadership, communications etc were decisive. However the German
victory also owed a lot to signals intelligence and codebreaking. Especially the solution, during the late 1930’s and in 1940, of the French military command’s ciphers gave the Germans valuable information on the location of the Allied units and was obviously used during the planning stage for the attack.
Notes:
(1). TICOM
report DF-187B, p6 and SRH-349 ‘The Achievements of the Signal Security Agency
(SSA) in World War II’, p31.
(3). EASI vol1
– ‘results of European Axis cryptanalysis’
(5). TICOM
report I-112, p6
(6). Bayerische
Staatsbibliothek: ‘Einzeldarstellungen aus dem Gebiet der Kryptologie’ - BSB
Cgm 9304 a
(7). TICOM
report I-176,
p2
(8). German
Foreign Ministry’s Political Archive - TICOM collection - file 3612 ‘Frankreich
1938 Arbeiten u.Notizen zu Code F90’
(9). German
Foreign Ministry’s Political Archive - TICOM collection - file 3684 ‘Frankreich
1938 ''F4ZCUW110'', Notizen zu Chiffre f. Verteidigungsbereich, m. Beispielen’
(10). German
Foreign Ministry’s Political Archive - TICOM collection - file 3661 ‘Frankreich
1939 Bericht betr. Entschlüsselung F90 Arb.-Blätter zu F135’
(11). TICOM
document T3661 - Föppl report, p5
(12). TICOM
report D-60, p4
Acknowledgments: I have to thank Jean-François
Bouchaudy for referencing the ‘Bulletin de l’ARCSI’ articles and Frode Weierud
for his analysis of the TICOM reports T3612, T3684 and T3661.
Additional information:
Link to chapter VI – ‘The French systems’ of SRH-361
great stuff !
ReplyDelete