Career
She worked for the Signals Intelligence Service throughout World World War II, during which time she played an important role in deciphering the Japanese cryptography machine Purple, and later worked on the Cold War-era Venona project She passed the necessary tests to become a government mathematician in 1939, and was hired by William F. Friedman to work as a cryptanalyst for the Army"s Signals Intelligence Service (SIS). Foreign eighteen months, she worked with other SIS codebreakers to decipher the code used by Purple, a Japanese cryptography machine, and ultimately played a key role in cracking the cipher in September 1940.
This enabled the construction of an analog machine by the SIS which in turn enabled the interception of almost all messages exchanged between the Japanese government and its embassies in foreign countries.
After the conclusion of World World War II, Feinstein continued to work at the SIS throughout the Cold War, trying to decode encrypted messages sent by the Soviet Komitet Gosudarstvennoy Bezopasnosti (Committee for State Security) and Main Intelligence Directorate (GRU). She made a significant breakthrough in the early stages of the Venona project, which allowed American cryptographers to recognize when an individual cipher key was reused, but resigned from the SIS in 1947.
After resigning from government cryptanalysis, she began working in the faculty of George Mason University, where she served as a professor of mathematics. She was posthumously inducted into the National Security Agency Hall of Honor in 2010, and an award in cryptology was established at George Mason University in her honor.
