SUNY Geneseo Department of Computer Science

Enigma Introduction

Thursday, March 13

Intd 105 13, Spring 2014
Prof. Doug Baldwin

Questions?

The novel

Questions? What’s happening?
- World War II; British cryptanalyst Tom Jericho is recovering from a nervous breakdown at Cambridge University (where he is in a position probably between that of graduate student and junior faculty member in a US university), after having worked on breaking German cryptography.
Historical background: Breaking German military ciphers to understand movements, particular of submarines targeting shipping in the Atlantic, was crucial to Britain’s ability to fight in World War II. Bletchley Park was headquarters for British cryptanalysis. This is where Jericho has been and what he has been doing and why he is under such pressure. German cryptosystems were all based on the Enigma machine.

The machine: what was Enigma?

Originally developed in Germany for commercial cryptography in the late 1920s
Based on a simple but powerful idea of wheels with electrical contacts that represent letters of the alphabet. Letters on one side of the wheel connect to different letters on the other, thus implementing a kind of substitution cipher.
Clever part comes from having several wheels that rotate relative to each other as in a mechanical odometer. Rotating one step after each letter means that every letter in a message is encrypted using a different substitution, thus foiling frequency analysis.

Wheels with electrical connections between front and back

Feeding ciphertext message “backwards” through the wheels decrypts it, as long as the wheels start in the same configuration as they started in when encrypting the message.
- In actual Enigmas, a “reflector” sent electrical signals coming out one end of the series of wheels back through them, meaning that input and output of the encryptor were physically the same place, so encryption and decryption were the same process: type plaintext in and read ciphertext out, or type ciphertext in and read plaintext out.
Plugboard did an additional set of fixed (i.e., not changing for each letter) letter-for-letter swaps on text going into and out of wheels. Added significantly to the number of possible machine settings a cryptanalyst would have to guess at
Adapted for military use in the 1930s.
Photo of an Enigma from BBC
Polish cryptanalysts made a lot of progress towards breaking Enigma prior to World War II
Many of the key Poles came to Britain after the war started and helped with British cryptanalysis
Bombe: machine that partially automated breaking an Enigma cipher
- Initially developed in Poland, refined by British

Try Enigma encryption/decryptionvia an online Enigma simulator

March 25: Library research session in Milne

Finish reading Enigma by March 27