The Kullback–Leibler divergence provides a critical measure for comparing probability distributions, yet Solomon Kullback established his initial reputation not in statistics, but as a central architect of American signals intelligence. One of the first three civilians hired by William F. Friedman at the Signal Intelligence Service, he fundamentally shaped the development of automated cryptanalysis.
Early Education and Recruitment
Born in Brooklyn in 1907, Kullback pursued an academic path at the City College of New York, completing his BA in 1927 and an MA in mathematics by 1929. He obtained a doctorate from George Washington University in 1934. Though he initially explored a secondary education teaching career, he found the work unfulfilling. His entry into professional mathematics followed a chance encounter with a Civil Service advertisement for junior cryptanalysts, leading to his appointment alongside Abraham Sinkov.
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At the Signal Intelligence Service, Kullback participated in intensive training programs held at Fort Meade. Assigned to work with Frank Rowlett, he focused on decrypting the RED cipher machine. The duo successfully reconstructed the machine’s pattern and keying systems using only intercepted transmissions. By 1942, now holding the rank of Major, Kullback visited Bletchley Park to consult with British counterparts on codebook systems and Enigma operations. Upon returning to the United States, he assumed leadership of the Japanese section.
Research and NSA Leadership
With the 1952 establishment of the National Security Agency, Kullback shifted his focus toward advancing high-speed processing technology. Managing a team of 60, he supervised technical pioneers such as Leo Rosen and Sam Snyder. Their efforts included the development of magnetic tape, drum memory, and compilers to facilitate multi-purpose computing, with specific applications for communications security. He served as the NSA Chief Scientist until his 1962 retirement.
Academic Contributions and Retirement
Following his government departure, Kullback returned to George Washington University as a professor. His seminal text, Information Theory and Statistics, originally released in 1959 by John Wiley & Sons, remained an influential resource, seeing republication by Dover Publications in 1968. During this period, he attained the rank of colonel, received the Wilks Memorial Award, and was inducted into the Military Intelligence Hall of Fame. He remained active in mathematics until his death in 1994 in Boynton Beach.
Fast facts
- Born: 1907, Brooklyn
- Died: 1994, Boynton Beach
- Education: City College of New York; George Washington University
- NSA Chief Scientist until: 1962
- Notable Publication: Information Theory and Statistics (1959)
- Professional Recognition: Fellow of the Institute of Mathematical Statistics (1942)
- Awards: Wilks Memorial Award
- Military Rank: Colonel
Questions readers ask
What was Kullback's role in cryptanalysis?
He was a lead cryptanalyst who broke the Japanese RED machine and later supervised the development of high-speed computing and communications security at the NSA.
What is the Kullback–Leibler divergence?
It is a mathematical measure of how one probability distribution differs from a second, named after Solomon Kullback and Richard Leibler.
Achievements
- Held posts at George Washington University
- Fields: cryptanalysis
