mjjoyce/enigma_cipher_machine

The enigma crate implements an Enigma machine cipher along with the components (i.e., rotors and reflectors) for the Wehrmacht and Luftwaffe versions.

Usage

CLI

The enigma binary takes text (encoded or otherwise) and an Enigma machine configuration string as input, runs the text through the configured machine, and outputs the result.

enigma -i "hello, how are you doing" -c "A;III-A-A,II-A-A,I-A-A;a-b"
LZFAD, AMT GPJ FND IFMJY

Encryption and decyption is handled in the same was due to the nature of Enigma.

enigma -i "LZFAD, AMT GPJ FND IFMJY" -c "A;III-A-A,II-A-A,I-A-A;a-b"
HELLO, HOW ARE YOU DOING

Configuration

The enigma configuration string specifies all details for the machine.

"A;III-A-A,II-A-A,I-A-A;a-b"

This configuration is laid out as through you're looking at an Enigma machine from the front and represents the reflect, rotor, and plugboard configurations.

The configuration string is broken up into three components.

<Reflector Id>;<Rotor Configurations>;<Plugboard mappings>

The Reflector Id is one of the Wehrmacht and Luftwaffe reflectors. See the Reflector page for valid options.

A rotor configuration specifies a rotor id and the position and ring location settings. See the rotor module page for valid rotor ids.

III-A-A
<Rotor Id>-<Position>-<Ring Location>

The plugboard mappings specify the character ports that a plug is connecting. For example, the following connects A and B and C to D on the plugboard. Note that the order doesn't matter.

<Reflector Id>;<Rotor Configuration>;a-b,d-c

API

EnigmaMachine and EnigmaMachineBuilder can be used to build and run an Enigma programmatically.

use enigma::machine::EnigmaMachine;

let builder = EnigmaMachine::builder();
let mut machine = builder
    .reflector("A")
    .plugboard(vec![('A', 'B')])
    .rotors(vec![
        ("I".to_string(), 0, 0),
        ("III".to_string(), 0, 0),
        ("II".to_string(), 0, 0),
    ])
    .build().unwrap();

let trans = machine.translate_text("Hello, how are you".chars());

Future Improvements

Only a portion of the available rotors and reflectors are currently implemented. Specifically, the Beta and Gamma rotors and the thin Kriegsmarine M4 reflectors are not implemented. The implementation of the machine will handle all of these without issue, including the fourth rotor of the Kriegsmarine M4.

Some cryptanalysis tooling would be fun to implement. See the Practical Cryptography and Computerphile links for some motivation.

Additional Details

There are a lot of amazing resources for studying the internal workings of the Enigma and the incredible work undertaken to break the code. The following contained useful technical details or inspiration when implementing this.

• Technical Details of the Enigma Machine, Cipher Machines and Cryptology
• Enigma Rotor Details, Wikipedia
• Quadram Statistics as a Fitness Measure, Practical Cryptography
• Cracking Enigma in 2021, Computerphile