Enigma Machine Breaker

A computer program that is capable of emulating an enigma machine, and of breaking the enigma cipher using brute-force methods. I programmed it as a major project for UNSW's COMP6841 "Extended Security Engineering" course.

The Enigma cipher was a complex cipher used by Germany in World War 2 to encipher classified information so that it could be sent through the air "safely". Alphabetic messages were encoded using an Enigma machine, which had over 150 trillion possible keys. This massive complexity was due to a number of components integrated into the machine:

  • A plug board where up to 10 plugs can be inserted to swap letters.
  • 3 rotors with a complex stepping pattern, meaning that the encoded letter changes with each keypress, with sequence repetition only happening after 17000 characters.
  • A reflector which maps all letters to a different letter, before sending the resultant letter back through the above components in reverse.

Emulation

My program is capable of emulating the enigma machine perfectly, with a modular design allowing for even more complex configurations (for example using a theoretically unlimited number of rotors).

$ # Encipher using reflector B, and 3 rotors (V starting at position X, I
$ # starting at position C, and II starting at position B)
$ enigma encipher B -r V:X I:C II:B
Hello, world! This is my super cool Enigma machine, programmed in Rust!
Jtdvt, zndgl! Jrvr cq ik ydkqk qmws Nxxxtx sylgzjn, kmfwdmfwcv gc Iqcx!

Due to the design of the machine, its ciphers are self-reciprocal, meaning that using the same key used to encipher text will produce the deciphered text. As such, we can decipher the above message by using the same configuration.

$ enigma encipher B -r V:X I:C II:B
Jtdvt, zndgl! Jrvr cq ik ydkqk qmws Nxxxtx sylgzjn, kmfwdmfwcv gc Iqcx!
Hello, world! This is my super cool Enigma machine, programmed in Rust!

Brute-force deciphering

My approach for brute-force deciphering is loosely based on security flaws, associated with the German use of the Enigma machine in World War 2.

Providing known information

In order to run a brute-force decipher, users need to specify all known information, using an _ underscore to represent unknown information. In World War 2, Germans often reused the majority of their key for a full day, so any known parts of the key can be provided to the brute force function, reducing the work it needs to perform.

Specifying message contents

Another historical security flaw from World War 2 was the Germans' inclusion of common repeated phrases such as greetings. Users of my program can specify known --msg-start, --msg-end and --msg-contains values, which are used to narrow down the search patterns.

$ enigma force _ -r _ _ _ --msg-start Hello
Jtdvt, zndgl! Jrvr cq ik ydkqk qmws Nxxxtx sylgzjn, kmfwdmfwcv gc Iqcx!
Done! Found 2 matches
1 :: A --rotor-ids III:I V:R III:D
Hello, tipwh! Tned lc wv noegz tfyo Apdlih djpmfgf, hylfkogiqw wn Mcbj!

2 :: B --rotor-ids V:X I:C II:B
Hello, world! This is my super cool Enigma machine, programmed in Rust!