 In 1950 Gleason returned to active duty for the Korean War , serving as a Lieutenant Commander in the Nebraska Avenue Complex ( which much later became the home of the DHS Cyber Security Division ) . His cryptographic work from this period remains classified , but it is known that he recruited mathematicians and taught them cryptanalysis . He served on the advisory boards for the National Security Agency and the Institute for Defense Analyses , and he continued to recruit , and to advise the military on cryptanalysis , almost to the end of his life . 
