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Code breaking

Code- and cipher-breaking have been in operation for centuries. However, cryptanalysis – the art of deciphering encoded messages – took on a new importance during WW2 as British boffins strived to reveal the true meaning of encrypted German military messages.

Photo: Hut 3 at Bletchley Park, Buckinghamshire in 1942. Here, civilian and service personnel worked together at code-breaking top-secret military communiques between Hitler and his armed forces. (SSPL/Getty Images)

Introduction

Code breaking

Highlights from BBC programmes Video (6)

More information about: Code breaking

Cryptography was used extensively during World War II, with a plethora of code and cipher systems fielded by the nations involved. In addition, the theoretical and practical aspects of cryptanalysis, or codebreaking, was much advanced.

Probably the most important cryptographic event of the war was the successful decryption by the Allies of the German "Enigma" Cipher. The first complete break into Enigma was accomplished by Poland around 1932; the techniques and insights used were passed to the French and British Allies just before the outbreak of the War in 1939. They were substantially improved by British efforts at the Bletchley Park research station during the War. Decryption of the Enigma Cipher allowed the Allies to read important parts of German radio traffic on important networks and was an invaluable source of military intelligence throughout the War. Intelligence from this source (and other high level sources, including the Fish ciphers) was eventually called Ultra.

A similar break into an important Japanese cipher (PURPLE) by the US Army Signals Intelligence Service started before the US entered the War. Product from this source was called MAGIC. It was the highest security Japanese diplomatic cipher.