During WWII
the US State Department used several cryptosystems in order to protect its
radio communications from the Axis powers. The main systems used were the
unenciphered Gray and Brown codebooks along with the enciphered codes A1, B1,
C1, D1 and the new M-138 strip cipher.
In the period
1940-1944 German, Japanese and Finnish codebreakers could solve State
Department messages (both low and high level) from
embassies around the world. The M-138-A
strip cipher was the State Department’s high level system and it was
used extensively during that period. Although we still don’t
know the full story the information available points to a serious
compromise both of the circular traffic (Washington to all embassies) and
special traffic (Washington to specific embassy). In this area there was
cooperation between Germany, Japan and Finland. The German success was made
possible thanks to alphabet strips and key lists they received from the
Japanese in 1941 and these were passed on by the Germans to their Finnish
allies in 1942. The Finnish codebreakers solved several diplomatic links in
that year and in 1943 started sharing their findings with the Japanese. German
and Finnish
codebreakers cooperated in the solution of the strips during the war,
with visits of personnel to each country. The Axis codebreakers took advantage
of mistakes
in the use of the strip cipher by the State Department’s cipher unit.
Traffic of
other US government agencies
Apart from
purely diplomatic traffic the Axis powers were also able to read some of the
messages of other organizations that were occasionally enciphered with State
Department systems. I’ve covered the compromise of the communications of the Office
of Strategic Services, the Office
of War Information and the Military
Intelligence Service but these were not the only agencies affected.
According to
US reports from 1943 and 1944 (1), separate M-138-A alphabet strips were used
by the State Department for messages of the Foreign
Economic Administration, War Shipping
Administration, Office
of Lend-Lease Administration and the War Refugee Board.
The
State Department files on the Strip Cipher (2) show that a set of strips titled
00-1 (and key table C) was
introduced in late 1943 for enciphering the confidential traffic of other US
government agencies. In January 1944 the sets 00-2 and 00-3 were sent
to the embassies in Algiers (Free French), Turkey, Egypt, UK, Calcutta,
Portugal, Spain, India, Sweden, Iran, Iraq, Beirut.
The 00-4 strips
replaced set 00-3 in October 1944.
Was the
traffic of these organizations also compromised? It seems so, as some German
decodes of State Department traffic contain information on economic matters and
Lend Lease shipments (3) and the book ‘Hitler, the Allies, and the Jews’ mentions several War Refugee Board
telegrams that were decoded by the Germans (4).
Unfortunately we will have to wait for the release of more classified
reports, from the NSA and the State Department, in order to assess the full
extent of this compromise.
Notes:
(1). NSA
Friedman collection: ‘Statement of cryptographic systems now in use by Department of State’ (dated November
1943) and NARA - RG 457- Entry 9032- box 1.384, file 'JCS Ad hoc committee
report on cryptographic security of government communications' (report
of June 1944)
(2). New developments in the strip cipher case
(2). New developments in the strip cipher case
(3). For example
in Decoded
US diplomatic messages from 1944 and German
special intelligence, the M-138 strip cipher and unrest in India
(4). ‘Hitler,
the Allies, and the Jews’, p200-201 - p265-267 - 287-288
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