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74 BLETCHLEY PARK AND BEYOND
Venona revealed the security-minded nature of the Soviets.
Much of their traffic was encrypted using a one-time pad system.
This was time-consuming and slow, but they were willing to put
in vast effort to protect their communications. This required huge
volumes of tear-off pads with sheet after sheet of random
numbers. The difficulty of generating thousands of sheets of truly
random numbers should not be underestimated, and no one is
clear how the Soviets made them. One individual has recalled
a room full of women simply shouting out any number that
came into their heads, but this seems improbable. Others have
described devices not unlike lottery machines, with numbered
balls. Whatever system was used, the logistical difficulties of
generating many thousands of one-time pads and distributing
them proved too much for wartime Russia. 7 Some time in early
1942, with Moscow on the verge of evacuation and much of
Soviet industry badly dislocated, operators began to run out of
pads. The KGB department that printed them committed the
fatal error of reprinting twenty-five thousand pages. This made
a small proportion of the messages, which should have been
unbreakable, vulnef3.ble to cryptanalysis. Far worse, they were
sent to KGB units as well as to military and diplomatic users.8
The Venona project that exploited this mistake began in
Washington. The Americans had collected Soviet messages during
the war, but they lacked time to work on them. On 1 February
1943 the US Army's code-breaking service, called the Signals
Intelligence Service, began a modest effort to see if it could
exploit Soviet diplomatic communications. The telegrams had
been collected at Arlington Hall, in Virginia, a former girls' school
which was commandeered by the Army as its main code-breaking
centre. Interest increased dramatically when it was discovered
that some of the streams of traffic related to espionage. In October
1943 a young code-breaker, Lieutenant Richard Hallock, a Signal
Corps reserve officer who had been a peacetime archaeologist
at the University of Chicago, was looking at Soviet commercial
traffic when he realised that the Soviets had committed a terrible
error and were reusing their pads. This was an astonishing