When the
United States entered WWII several cryptosystems were in use by its armed
forces and diplomatic service. The Army and Navy used a small number of SIGABA cipher machines
for their high level traffic and had to rely on a large number of hand systems,
such as the M-138-A
and M-94 strip ciphers and the War
Department Telegraph Code 1919, Military
Intelligence Code, War Department Confidential Code codebooks, for the rest
of the traffic. The State Department relied almost exclusively on hand systems,
specifically the codebooks A1, B1, C1, D1, Gray, Brown and the M-138-A strip
cipher.
In the course
of the war modern cipher machines were designed and built to replace the old
systems and securely cover all types of traffic. In 1942 the M-209 device
was used in the field and in 1943 the cipher teleprinters Converter M-228 - SIGCUM and
SIGTOT were
introduced in communications networks. In the summer of ’43 a new speech
privacy device called SIGSALY became
operational and the first system was used on the link
Pentagon-London. In late 1943 the CCM - Combined
Cipher Machine was used in the Atlantic and in 1944-45 the British
relied on the CCM as much as they did on their own Typex.
By the end of
the war the Americans were using several types of cipher machines, all offering
a high level of security. William Friedman,
head of cipher research at the Army Security Agency, stated in his 1945 reports
that the primary US cipher machines SIGABA and Converter M-228 had proven
completely secure against enemy cryptanalysts.
‘We come
now to what, in the circumstances, must be considered as the strongest and most
reliable evidence—that which is inferential in and is based upon German
cryptography itself. We know so much about their practices that we can deduce
and assess their cryptographic theories and thus determine the stage of
development they have reached not only in cryptography but also in
cryptanalytics. The overwhelming evidence is that they are far behind us and
have no appreciation of solution techniques which we now regard as commonplace’.
‘To summarize: At the risk of sounding boastful,
it will be stated that the Japanese are not as good as the Germans, and the
latter are not as good as we are in cryptography and especially in
cryptanalysis…… the
conclusion must therefore be clear: They
cannot read and are not reading our high-grade cipher traffic’.
‘We know now from Ticom reports that neither
the Japanese nor the Germans had the slightest success in their efforts to
solve messages in the Sigaba, though the Germans certainly tried hard enough.
The absolute security of Army and Navy high command and high echelon
communications throughout the war was made possible by the Sigaba’.
‘Results of Ticom operations have established
that neither the Germans nor the Japanese were successful in their efforts to
solve our Sigcum traffic, despite its great volume, and it is my belief that
had we used this machine for secret radio-teletype communications no serious
harm to our security would have followed’.
Was Friedman
correct? Were all high grade US cipher machines secure during the war?
