Genevieve Grotjan Feinstein

Career

Feinstein discovered a passion for mathematics at a young age and aspired to become a math teacher. She graduated from the University at Buffalo summa cum laude in February 1936 with a mathematics degree. Unable to find a teaching job, she took a position as a statistical clerk at the Railroad Retirement Board. Her high score on a civil service mathematics test in 1939 got the attention of William F. Friedman, who hired her to work as a junior cryptanalyst for the army's Signals Intelligence Service (SIS). For eighteen months, she worked with other SIS codebreakers to analyze the encryption system used in the Japanese Type B Cipher Machine, code named Purple by the SIS She played a key role in cracking the cipher, discovering cyclical behavior in the code on September 20, 1940. This enabled the construction of an equivalent 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. Purple-encoded reports from Hiroshi Oshima, the Japanese ambassador in Berlin, were a main source of intelligence about Axis plans.

In 1946, she was awarded the Exceptional Civilian Service Award from Brig. Gen. Paul Everton Peabody for her wartime service.

She was later assigned to the Venona project, trying to decode encrypted messages sent by the Soviet KGB and Main Intelligence Directorate (GRU). She made a significant breakthrough in November 1944, which allowed American cryptographers to recognize when an individual one time pad cipher was (improperly) reused. After the conclusion of World War II, Feinstein continued to work at the SIS, as the Cold War began, but resigned in 1947. After resigning from government cryptanalysis, she joined the faculty of George Mason University, where she briefly served as a professor of mathematics.