William F. Friedman

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William Friedman

William Frederick Friedman (September 24, 1891November 12, 1969) was a cryptologist in the US Army. Many consider Friedman one of the greatest cryptologists of all time, and his application of statistical methods to codebreaking one of the most significant advances in the field.

During the 1930s, Friedman ran the research division of the Army's Signals Intelligence Service (SIS), and its follow-on services right into the 1950s. He supervised the breaking of the Japanese PURPLE cipher in the late 1930s, and the results provided considerable intelligence about Japanese diplomacy at the highest level throughout World War II and afterwards.


Early life

Friedman was born Wolfe Frederick Friedman in Kishinev, Moldavia, the son of a postal worker who migrated to Pittsburgh in 1892. Three years later Wolfe's name was changed to William. He studied at the Michigan Agricultural College in East Lansing and received a scholarship to work on genetics at Cornell University. Meanwhile George Fabyan, who ran a private research laboratory to study any project that caught his fancy, decided to set up his own genetics project and was referred to Friedman. Friedman joined Fabyan's Riverbank Laboratories outside Chicago in September 1915. As head of the Department of Genetics, one of the projects he ran studied the effects of moonlight on crop growth, and so he experimented with the planting of wheat during various phases of the moon.

Initial work in cryptology

Another of Fabyan's pet projects research into the coded messages which Sir Francis Bacon had allegedly hidden in various texts during the reign of Elizabeth I and King James. The research was carried out by an Elizabeth Wells Gallup. Believing that she had detected that many of Shakespeare's works also included such hidden messages, Gallup became convinced that Bacon wrote many, if not all, of William Shakespeare's works. Friedman had become something of an expert photographer while working on his other projects, and was asked to travel to England on several occasions to help Gallup photograph historical manuscripts during her research. At this point he became fascinated with cryptology, while he courted Elizebeth Smith, Mrs. Gallup's assistant and an accomplished cryptologist. They married, and soon after he became the director of the Department of Codes and Ciphers as well as of the Department of Genetics at Riverbank.

With the entry of the United States into World War I, Fabyan offered the services of his Department of Codes and Ciphers to the government. No Federal department existed for this kind of work (although both the Army and the Navy had had embryonic departments at various times), and soon Riverbank became the unofficial cryptographic center for the US Federal Government. During this period the Friedmans cracked a code used by German-funded Hindu radicals in the US who planned to ship arms to India to gain independence from Britain. Analysing the format of the messages, Riverbank realized that the code was based on a dictionary of some sort, a common encryption technique. The Friedmans soon managed to decode most messages, but only long after the case had come to trial did the book itself come to light: a German-English dictionary published in 1880.

The United States government decided to set up its own code-breaking service, and sent Army officers to Riverbank for training under Friedman. To support their training, Friedman produced a series of technical monographs, completing seven by early 1918. He then enlisted in the Army, and travelled to France to serve as the personal codebreaker for General John J. Pershing. He returned to the US in 1920 and published an eighth monograph, "The Index of Coincidence and its Applications in Cryptography", which is considered to be the most important single publication in modern cryptology to that time. The texts he wrote for Army cryptographic training were well thought of and remained classified for many decades.

In 1921 he joined the government's American Black Chamber where he was placed in charge of researching new codes and ways to break them, and in 1922 he was promoted to head the Research and Development Division. After the dissolution of the Black Chamber in 1929, Friedman moved to the Army's Signals Intelligence Service (SIS) in a similar capacity.

Solution of cipher machines

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Friedman with an AT&T cipher machine

During the 1920s a series of new cipher machines gained popularity, based largely on typewriter mechanicals attached to basic electrical circuitry - batteries, switches and lights. An early machine had been the Hebern Rotor Machine, designed in the US in 1915 by Edward Hebern. This system offered such security and simplicity of use that Hebern heavily promoted his company to investors, feeling that all companies would soon be using them and his company would clearly be successful. But the company went bankrupt when the war ended, and Hebern eventually landed in prison, convicted of stock manipulation.

Friedman realized that the new rotor machines would be important, and devoted some time to analysing Hebern's design. Over a period of years he discovered a number of problems common to most of the rotor machine designs. Examples of some dangerous features included having the rotors turn once with every keypress, and positioning the fast rotor (the one that turns with every keypress) at either end of the rotor stack. In this case, by collecting enough cyphertext and applying a standard statistical method known as the kappa test, he showed that he could, albeit with great difficulty, crack any code generated by such a machine.

Friedman then used his understanding of the rotor machines to develop several of his own that remained immune to his own attacks. He eventually developed nine designs, six of which remain still secret today. Some of his inventions while developing these systems only gained patents decades later, since the Defense Department regarded them as so critical that granting a patent would harm national security. The culmination of various designs, including the M-325, resulted in the SIGABA, which became the US's highest security encryption system during World War II. It is believed that the machine was never broken during WWII.

In 1939 the Japanese introduced a new cypher machine system for their most secure diplomatic traffic to and from important embassies, replacing an earlier system SIS referred to as "RED". The new cypher, PURPLE, proved quite difficult to crack. The Navy's OP-20-G and the SIS thought it might relate to the earlier mechanical cypher machines, and the SIS set about attacking it. After spending several months studying the cyphertexts and trying to discover the underlying patterns. Eventually, in an extraordinary achievement, the SIS team figured it out. PURPLE did not use rotors, unlike the German Enigma or the Hebern design, but used stepper switches like those used in automated telephone exchanges. Leo Rosen of the SIS built a machine and, astonishingly, used the very same model of telephone stepper switch that the Japanese designer had used.

By the end of 1940 Friedman's team at the SIS had constructed an exact analog of the PURPLE machine, even though they had never seen one. With an understanding of PURPLE and duplicate machines of their own to use, the SIS could then decrypt an increasing amount of the Japanese traffic. One such intercept was the message to the Japanese Embassy in Washington ordering an end (on December 7th 1941) to the negotiations with the US. The message gave a clear indication of impending war, and was to have been delivered to the US State Department only hours prior to the attack on Pearl Harbor.

The pressure of his responsibilities, including the PURPLE effort was too much and Friedman entered a hospital in 1941 with a nervous breakdown. After his release, he served as Director of Communications Research for the SIS for the rest of the war. Friedman visited the British codebreaking operations at the Government Code and Cypher School at Bletchley Park in 1941. He exchanged information on the techniques for attacking PURPLE for the British information on how they had broken the Enigma.

After World War II

Following the WWII, Friedman remained in government signals intelligence. In 1949 he became head of the code division of the newly-formed Armed Forces Security Agency (AFSA), and in 1952 become the chief cryptologist for the National Security Agency (NSA) when it formed to take over from the AFSA.

Friedman retired in 1956 and turned his attention, with his wife, to the problem that had originally brought them together: examining Bacon's codes. In 1957 they wrote The Shakespearean Ciphers Examined, in which they demonstrated flaws in Gallup's work and in the work of others who sought to find hidden cyphers in Shakespeare's work. His health began to fail in the late 1960s, and he died in 1969.

Mr. Friedman is a member of the Military Intelligence Hall of Fame.


  • Ronald W. Clark, The Man Who Broke Purple: The Life of Colonel William F. Friedman, Who Deciphered the Japanese Code in World War II, 1977.
  • Reprints of Friedman's publications are available from Aegean Park Press (http://www.aegeanparkpress.com/)

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