The Life and Work of the American Cryptologist William Friedman

William Friedman (1891−1969) is rightfully considered to be the father of American Cryptology. Born in the Russian Empire, from 1893 lived in the USA, and trained as a geneticist, William Friedman along with his wife Elizabeth Smith Friedman made great contributions to cryptology. Friedman was the U.S. Army cryptographer in charge of the research division of the Army's Signal Intelligence Service (SIS), and for over 30 years William Friedman was instrumental in providing cryptological security to the US Government. Notably, William Friedman came up with a clever idea to use a particular formula from probability theory, The Index of Coincidence, as an aid in deciphering messages. The war with Japan heavily involved codebreaking, and Friedman and his group successfully decrypted the Japanese Navy communications and actually reconstructed the Japanese cipher machine Purple giving cryptanalysis the decisive role in the victory at Midway in 1942. After WWII, William Friedman continued his work in cryptology, classified for many years. After declassification, most of his contributions are made public and many were published in digitized form. William Friedman’s dedication to his duties was unparalleled and serves as an example to young researchers everywhere.