The use of codes in writing can be traced back more than 4,000 years to the Egyptians. Examples of writing in codes can be found in numerous cultures and civilizations including the Greek and Roman empires. The first sustained efforts to develop a system for writing in code appeared in 855 AD when an Arab book containing several cipher alphabets was published. The practice of communicating through code did not reach western civilization until the Middle Ages, and it has remained in continuous use since that time. During the Renaissance many different methods for making and breaking codes were developed, some of which served as the foundation for modern codebreaking. The invention of the telegraph machine in 1844 reinforced the importance of using codes to communicate sensitive information.
Despite the increasing use of codes until the outbreak of WWI, many countries had not yet begun to organize departments devoted to codebreaking activities. Even after the United States declared war in 1917, the army did not have a program for training soldiers in codebreaking. In the aftermath of World War I many countries, including the United States, continued their codebreaking activities. Prior to and after the war William F. Friedman published a series of articles that applied scientific and statistical principles to codebreaking that would serve as the foundation for modern codebreaking. These principles when employed by William Friedman, Alan Turing, and others during World War II, led to the breaking of the Japanese PURPLE code and the Nazi ENIGMA code which gave the Allies a significant strategic advantage, and played an important part in the Allied victory. The code machines developed during World War II operate according to the same basic principles that are used in today’s complex codebreaking devices.
William and Elizebeth Friedman
William F. Friedman, considered to be the pioneer of modern codebreaking, and his wife Elizebeth Smith Friedman, a noted code breaker in her own right, began their codebreaking careers at Riverbank Laboratories in Geneva, Illinois, where they attempted to identify a code believed to be hidden in the plays of William Shakespeare. While at Riverbank William Friedman wrote a series of articles on codebreaking that showed the effectiveness of using scientific and statistical principles. William Friedman served in France during World War I where he broke German codes at General John J. Pershing’s headquarters. As head cryptologist for the War Department before and during World War II he led a team that broke the Japanese diplomatic cipher known as PURPLE. After the war, Friedman became the head Cryptologist at the National Security Agency from it formation in 1952 until his retirement in 1956.
Elizebeth Friedman worked for the Treasury Department during the 1920s and 1930s to break codes used by gangs attempting to smuggle alcohol into the United States during Prohibition. She served as a key witness in a number of high profile cases, and her work led to the conviction of many of the smugglers. Other cases in which Elizebeth Friedman’s codebreaking skills played a key role include the break-up of a Canadian opium smuggling ring and the conviction of a United States citizen spying for the Japanese during World War II. She was transferred to the Navy to assist with code work for the remainder of the war. Later she served as a consultant and created communication security systems for the International Monetary Fund.
PURPLE was the name given to the cipher system used by the Japanese government for its most secret communications. Although the Japanese PURPLE cipher is not as well known as the Nazi ENIGMA code, it is considered to be more complex. The team assembled to break the PURPLE cipher, led by William F. Friedman, began receiving messages using the PURPLE cipher in 1937. As the team acquired more messages, it was able to test theories about how the cipher could be broken. Friedman’s team completely deciphered a message for the first time on September 25, 1940. The team then turned their attention to constructing a replica of the machine that produced the PURPLE cipher and determining the keys that were used to change a message from cipher to plain text. By the end of 1940 the United States had the ability to read any message the Japanese sent using the PURPLE cipher, which gave US leaders a huge advantage in decision making and planning during the war.
Alan Turing and Bletchley
Alan Turing was instrumental in the breaking of the German ENIGMA cipher during World War II. His work on breaking the ENIGMA code began in September 1938 at the Government Code & Cipher School at Bletchley Park. Turing was instrumental in the development of the bombe, which was the most important automated device used to break messages produced using the ENIGMA cipher. The first bombe was installed at Bletchley Park on March 18, 1940. Turing was also working on breaking the German naval ENIGMA which had the most complex indicator system used by the Nazis. By December 1939 he had made an important breakthrough in determining how the indicator system worked. He traveled to the United States from November 1942 to March 1943 to advise on the construction of American codebreaking devices. When Turing returned to Bletchley Park he served in the capacity of general consultant for cryptanalysis. He was also involved in the development of a portable voice scrambler, but the project was not finished until the war was almost over so it was not adopted for widespread use. After the war Turing worked on the design of the Automatic Computing Engine and the development of stored computer programs. Turing’s work with computers after the war has led many to consider him the father of computer science.
The earliest attempts to break the ENIGMA cipher took place in Poland in response to Germany’s increased aggressiveness. Near the end of 1932 Marian Rejewski attempted to break the ENIGMA cipher, and with the aid of stolen German code manuals and monthly keys, was able to break the cipher fairly quickly. As the Germans continued to increase the complexity of the ENIGMA machines, Rejewski worked to devise new methods by which the ciphers could be broken. The German decision to increase the number of rotors used in the ENIGMA machine in 1938 significantly reduced the number of coded messages that the Poles could break. As war with Germany became increasingly likely, the Poles held a conference with the British and the French in which they shared all their work on the breaking the ENIGMA cipher.
When the British began working on breaking the ENIGMA cipher at Bletchley Park, they sought to improve the Polish methods that relied on the repetition of the indicator in a message. The “bombe,” designed by Alan Turing, was developed in 1939 and aided codebreaking efforts by reducing the number of possible combinations that required further analysis to a manageable number. The number of bombes grew steadily throughout the war until there were 210 in operation by the end of the war. In March 1941 the Women’s Royal Navy Service (Wrens) began operating the bombes at Bletchley Park and by the end of the war more than 2,000 Wrens were involved in this work. The risk of bombing at Bletchley Park was high, so most of the bombes were operated from other locations and information was sent to Bletchley Park by teleprinter links. The breaking of the ENIGMA cipher is believed to have helped the Allies defeat Nazi Germany two years earlier than they would have without breaking it.