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Enigma Code Broken

Contributor: C. Peter Chen

ww2dbaseThe Enigma machine was a device first commonly used in the 1920s. With a series of mechanical and electrical systems, each keystroke pressed on its keyboard was transformed into a letter using one algorithm, while the subsequent keystroke was derived into another letter with yet another algorithm. The encryption method was prone to error either by the person entering the message or the one deciphering it, but it also ensured that unauthorized interceptors of the message would take so long to decipher the message that the intelligence would become worthless due to the lapse of time. The Germany military began using Enigma machines starting in the mid- to late-1920s, developing more complex algorithms to increase the security of the encryption. The German Navy was the first to use the Enigma machine. In 1928, the German Army began their version as well. By 1939, the German military and intelligence services each made significant improvements to their encryption algorithms, employing about 100,000 machines across all services.

ww2dbaseEnigma code was not perfect, however. British code breaker and professor Dilly Knox claimed to have broken the commercial version of the Enigma machine in the 1920s, and the Polish military had broken the German Army version of the code some time in the mid-1930s. On 25 Jul 1939, the Poles offered the British and the French their understanding of the decryption process. This knowledge sharing allowed the British to quickly setup a decryption effort that eventually came to be known under the code name "ULTRA". The code name signifies that fact that any knowledge of the British understanding of the German encryption code was considered more privileged than the rank of "most secret". With headquarters in Bletchley Park in Milton Keynes, Buckinghamshire, England, United Kingdom about 50 miles north of London, the British cryptographers worked hard to decipher the remaining and more complex versions of the German Enigma code. Very soon, the British cryptographers caught a break: they had come to realize that out of lack of discipline many German messages were sent every day with the exact same encryption, which gave the code breakers a constant flow of messages for them to work with. Had the Germans changed the rotors on their Enigma machines more frequently, the British might not have had enough information to work with to break the code. By late Jan 1940, the ULTRA program was fairly confident that they now possess the power to decrypt most German military codes at that time. This was considered a major turning point in the intelligence realm of the war.

ww2dbaseThe British were also very careful on what decrypted information to take advantage of. They concluded that had they jumped on every piece of information they could decipher, the Germans would quickly come to realize that their code had been broken, and would most definitely change their entire code set overnight. Therefore, while ULTRA had provided many pieces of intelligence on the movements of German submarines and other naval vessels, for example, only those that they could come up with a cover story were attacks. Sometimes the cover story involved a lucky scouting plane that came across a surfaced submarine, and sometimes a civilian fishing vessel was the key to a successful British raid on a supply convoy to North Africa.

ww2dbaseEven though the German code changed a number of times during the course of the war, such as the code change ordered by German Admiral Karl Dönitz in 1940, the British code breakers working on the foundation set by their Polish forerunners were able to provide valuable information to the Allied cause. By Aug 1943, the Allies were generally breaking Enigma messages with relative ease.

ww2dbaseGerman Efforts to Break Allied Codes

ww2dbaseJust as the Allies attempted to break German communications, the Germans attempted the same, and with great success. Talented radioman Wilhelm Tranow had broken British Royal Navy's 5-digit code back in 1935, and in Dec 1941, Beobachtungsdienst (B-Dienst) of the German Department of Naval Intelligence, under the leadership of Tranow, broke British Naval Cypher No. 3. The British had no clue that their code had been broken until a deciphered Enigma messaged revealed that the Germans were changing a particular plan after having intercepted British naval communications; the Royal Navy was not able to communicate securely until Naval Cypher No. 5 was put in use in Jun 1943. In Mar 1943, the US Navy had a similar revelation, realizing that the Germans were reacting very quickly based on orders being sent to ships on the high seas via radio. After the war, Karl Dönitz noted that half of his intelligence during WW2 came from deciphered Allied messages. After 1943, however, German codebreaking efforts generally yielded very little results as Allied encryption methods became more sophisticated.

ww2dbaseSources:

David Kahn, Seizing the Enigma

Wikipedia

Last Major Update: Feb 2006

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