How did Allied cryptanalysts break the Enigma code?

The cryptanalysis of the Enigma machine allowed the Western Allies during World War II to read substantial volumes of encrypted Axis military communications, yielding intelligence codenamed Ultra. The cipher was first broken in December 1932 by Polish mathematician Marian Rejewski using permutation group theory and intelligence material. Later, British efforts at Bletchley Park, involving mathematicians like Alan Turing and automated electromechanical bombes, scaled up decryption to support Allied military operations significantly.

What we know

• The Enigma cipher system was first broken in December 1932 by mathematician Marian Rejewski at the Polish General Staff's Cipher Bureau, using mathematical permutation group theory combined with French-supplied intelligence material obtained from German spy Hans-Thilo Schmidt. [2]
• Alan Turing provided much of the original thinking that led to the upgrading of the Polish cryptologic bomb used in decrypting German Enigma ciphers at Bletchley Park. [2]
• Good operating procedures, properly enforced, would have made the plugboard Enigma machine unbreakable to the Allies at that time. [2] · medium confidence
• The introduction of a fourth rotor by the Kriegsmarine for its U-boats resulted in a prolonged period when those specific messages could not be decrypted, until cipher keys were captured and faster US Navy bombes were employed. [2]
• The Enigma machine used an electromechanical rotor mechanism that changed electrical connections with each keypress, meaning every letter was encrypted with a different cryptographic key. [4]

Where to go next

• whoWho was Marian Rejewski?
• how it workedWhat was the Enigma machine mechanism?
• whereWhat was Bletchley Park?
• compared withHow did the Lorenz cipher differ from Enigma?
• what followedWhat impact did Ultra intelligence have on World War II?
• an unexpected connectionHow did a spy named Hans-Thilo Schmidt help crack Enigma?German intelligence material supplied by a spy was combined with advanced mathematical permutation group theory by Polish cryptographers to break the Enigma code initially.

Sources

• [1]cryptanalysis of the Enigma (Wikidata Q2665859) · CC0 1.0
• [2]Cryptanalysis of the Enigma · CC BY-SA 4.0
• [3]Cryptanalysis · CC BY-SA 4.0
• [4]Enigma machine · CC BY-SA 4.0
• [5]Cryptanalysis of the Lorenz cipher · CC BY-SA 4.0