Solomon Kullback Solomon Kullback ( 19071994 ) was an American cryptanalyst and mathematician , who 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 the George Washington University . The Kullback - Leibler divergence is named after Kullback and Richard Leibler . Life and career . Kullback was born in Brooklyn , New York and attended Boy ' s High School there . He then went to City College of New York , graduating with a BA in 1927 and an Master of Arts in math in 1929 . He completed a doctorate in math from George Washington University in 1934 . His intention had been to teach , and he returned to Boy ' s High School to do so , but 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 . Once they had completed the training , the 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 cipher machine messages . Almost overnight , they 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 , Kullback , by then a Major , was sent to Britain . He learned at Bletchley Park that 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 National Security Agency ( NSA ) was formed in 1952 , Rowlett became chief of cryptanalysis . The primary problem facing research and development in the post - war period was development of high - speed processing equipment . Kullback supervised a staff of about 60 , including such innovative thinkers in automated data processing 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 communications security ( COMSEC ) materials . Retirement . Solomon Kullback retired from NSA in 1962 , and focused on his teaching at George Washington University and publishing new papers . A colonel , he is a member of the Military Intelligence Hall of Fame . 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 . "