Solomon Kullback

Dr Solomon Kullback (1903–1994) was a US cryptanalyst and mathematician.

Kullback was was one of the first three employees hired by William F. Friedman at the US Army's Signal Intelligence Service (SIS) in the 1930s, along with Frank Rowlett and Abraham Sinkov. He went on to a long and distinguished career at SIS and its eventual successor, the National Security Agency (NSA). Kullback was the Chief Scientist at the NSA until his retirement in 1962, whereupon he took a position at Georgetown University.

The Kullback-Leibler divergence is named after Kullback and Richard Leibler.

Solomon Kullback attended Boy's High School in Brooklyn, then City College of New York. His intention had been to teach, and he returned to Boy's High to do it, but soon found it not to his taste; he discovered his real interest was using mathematics, not teaching it.

At the suggestion of Abraham Sinkov, who showed him a Civil Service flyer for "junior mathematicians" at US$2,000 per year, he took the examination. Both passed, and were assigned to Washington as junior cryptanalysts.

Upon arrival in Washington, Kullback was assigned to William F. Friedman. Friedman had begun an intensive program of training in cryptology for his new civilian employees. For several summers running, the SIS cryptanalysts attended training camps at Fort Meade until they received commissions as reserve officers in the Army. Kullback and Sinkov took Friedman's admonitions on education seriously and spent the next several years attending night classes; both received their doctorates in mathematics. Afterward, Kullback rediscovered a love of teaching; he began offering evening classes in mathematics at George Washington University from 1939 on, and found a new pleasure in teaching.

Once they had completed the training, these three were put to the work for which they had actually been hired, compilations of cipher or code material for the U.S. Army. Another task was to test commercial cipher devices which vendors wished to sell to the U.S. government.

Kullback worked in partnership with Frank Rowlett against RED messages. Almost overnight, these two unravelled the keying system and then the machine pattern -- with nothing but the intercepted messages in hand. Using the talents of linguist John Hurt to translate text, SIS started issuing current intelligence to military decision-makers.

In May 1942, five months after Pearl Harbor, now-Major Kullback was sent to Great Britain to expedite these exchanges. Kullback learned how the British were producing intelligence of high quality by exploiting the Enigma machine. He also cooperated with the British in the solution of more conventional German codebook-based systems. Shortly after his return to the States, Kullback moved into the Japanese section as its chief.

When the NSA was formed in 1952, Rowlett became chief of cryptanalysis. The primary problem facing R&D in the post-war period was development of high-speed processing equipment. Kullback supervised a staff of about 60, including such innovative thinkers in ADP development as Leo Rosen and Sam Snyder. His staff pioneered new forms of input and memory, such as magnetic tape and drum memory, and compilers to make machines truly "multi-purpose." Kullback gave priority to using computers to generate COMSEC materials.

Solomon Kullback retired from NSA in 1962. He now focused directly on his teaching at George Washington University. His list of publications on statistics, already long, grew ever more extensive.

COL Kullback is a member of the Military Intelligence Hall of Fame.

Solomon Kullback is remembered by his colleagues at NSA as straightforward; one described him as "totally guileless, you always knew where you stood with him." One former NSA senior recalled him as a man of unlimited energy and enthusiasm and a man whose judgment was usually "sound and right."de:Solomon Kullback