Enigma Machine

An Enigma machine is any of a family of related electro-mechanical rotor cipher machines used for the encryption and decryption of secret messages. Enigma was invented by German engineer Arthur Scherbius at the end of World War I. The early models were used commercially from the early 1920s, and adopted by military and government services of several countries — most notably by Nazi Germany before and during World War II. Several different Enigma models were produced, but the German military models are the ones most commonly discussed.

In December 1932, the Polish Cipher Bureau first broke Germany's military Enigma ciphers. Five weeks before the outbreak of World War II, on 25 July 1939, in Warsaw, they presented their Enigma-decryption techniques and equipment to French and British military intelligence. From 1938, additional complexity was repeatedly added to the machines, making the initial decryption techniques increasingly unsuccessful. Nonetheless, the Polish breakthrough represented a vital basis for the later British effort. During the war, British codebreakers were able to decrypt a vast number of messages that had been enciphered using the Enigma. The intelligence gleaned from this source, codenamed "Ultra" by the British, was a substantial aid to the Allied war effort.

The exact influence of Ultra on the course of the war is debated; an oft-repeated assessment is that decryption of German ciphers hastened the end of the European war by two years. Winston Churchill told the United Kingdom's King George VI after World War II: "It was thanks to Ultra that we won the war."

Although Enigma had some cryptographic weaknesses, in practice it was only in combination with procedural flaws, operator mistakes, captured key tables and hardware, that Allied cryptanalysts were able to be so successful.