Cryptography
Before the Age of Radio, much more difficult to intercept cable traffic
Radio potentially places large numbers of encrypted messages in the
hands of the cryptanalysts
This is the key to breaking the code!
British Admiralty Room 40: Codebreaking Room
Enigma Machine
Existence of ULTRA {"Very Special Intelligence") first revealed in
1974! Changed completely the way we view the history of WW II
Combined encoding/decoding machine
Five rotor system, three in use at any time
How it worked and why it was hard to crack
Use of per message keys makes analysis difficult
But patterns provide the way in: doubly encrypted message keys
Poles reverse engineer a stolen Enigma machine
Invention of the Bombe: mechanical device to exhaust all enumerations
New Enigma stumps the Poles who turn to the British (1939)
Bletchley Park
- Guessing the day key: cillies—common three letter sequences
- Human operator weakness!
- Rules of usage also limit the alternatives
- Stereotypical message structure helps too
- Turing’s idea: the crib--<common plain text, encrypted text>
- If found, then could determine Enigma settings
- Compute the transformation in parallel: Turing’s Bombe
- 10 May 40: Germans change their message key scheme
- Naval codes hardest to break—more sophisticated Enigma used
- Battle of Atlantic was being lost! Solution: pinch the codebooks!
Japanese Codes
Page last modified 28 January 2003, by Randy
H. Katz, randy@cs.Berkeley.edu