Chance Encounters

How random numbers have influenced spies, scientists and reality itself.

By Tim Folger|Friday, August 17, 2018

If it hadn’t been for a shortfall in the supply of random numbers, one of history’s most infamous spy rings might never have been exposed. The shortage occurred in late 1941, two years after the start of World War II. With Hitler’s invading armies poised to overrun Moscow, Soviet leader (and erstwhile bank robber) Joseph Stalin ordered key personnel to evacuate the capital. In the chaos that followed, the NKVD — Stalin’s intelligence agency and forerunner of the KGB — made a mistake that would doom all the Soviet agents who would infiltrate the Manhattan Project, the top-secret American effort to build an atomic bomb.

The error involved the NKVD’s codebooks, known as one-time pads, which used random numbers to scramble letters, words and phrases. The random-number key to any particular one-time pad was known only to the sender and recipient. Without it, the encoded message couldn’t be deciphered. As the name suggests, one-time pads were meant to be used once and then destroyed. Used properly, they were completely unbreakable. But making them required the laborious printing of volumes of random numbers. No one knows exactly how the Soviets produced random numbers — computers were still in their infancy. According to some accounts, the NKVD employed a roomful of women who would blurt out numbers haphazardly, or they may have used something like a lottery machine, with numbered balls. This much is known: Their schemes failed to meet demand.


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