Team Name: team13 Programmer: 陳則凱 b Tester: 劉典恆 b
What is Enigma Machine? An Enigma machine is a electro- mechanical rotor cipher machines used for the encryption and decryption of secret massages.
Some History (1) In World War II, the Nazi military employed an encryption scheme that addressed the weakness of substitution ciphers. The scheme, implemented by typewriter sized devices known as Enigma machines, gave the Nazis a tactical advantage that greatly contributed to their early success in the war.
Some History (2) Efforts to break the Enigma code led to the development of the first electronic computers at Bletchley Park, England: the Bombe (designed by Alan Turing) and its successor, Colossus (designed by Tommy Flowers). Using computers, the Allies were eventually able to break the Enigma code, giving them an intelligence edge that changed the balance of the war.
What do we want to do? We want to write a program to simulate the Enigma machine. Extra: Try to write a program to decrypt the secret code produced by the Enigma machine.
Why is it worth doing? Cryptography has played an important role in the history of computing, from motivating the development of the first electronic computer to enabling secure Web-based communication and commerce. This program enable us to know the role of encryption in military and computing history, and have a deep look into the mechanism of Enigma machine. The needs of data protection.
How It Works? The Basic Idea (1) The Caesar Cipher Each letter in the alphabet would be encoded using the letter n position later in the alphabet. Example: When n = 3, a b c d e f d e f g h i Weakness: The pattern is too regular, easy to break the code.
How It Works? The Basic Idea (2) Substitution Ciphers A code in which one letter of the alphabet is substituted for another (in random). Example: a b c d e f h j a s d b Weakness: Not all letters are equally likely in text, so the relative frequency of characters in the coded message can provide clues for decoding.
How It Works? The Basic Idea (3) Rotating Ciphers After each letter is encoded, the key is rotated so that the first character is moved to the end. Example: a b c d e f h j a s d b encode: a a a h j a encode: a b c h a d
How It Works? The Basic Idea (4) A Simple Enigma Model It is a combination of three rotating rotor (wheel). The inner rotor rotate one step after every single character is encrypted. The middle rotor rotate one step after the inner rotor complete a round of rotation. Same for the outer rotor.
How It Works? The Basic Idea (5) To encrypt a character, 1. Find the character on the inner rotor 2. Note the corresponding character on the outer ring 3. Find that character on the middle rotor 4. Output the corresponding character on the outer ring. Reverse procedure to decrypt the message.
How It Works? The Basic Idea (6) Enigma machine paper model Consisting of three rotor, each with a notch on it, a spindle with a reflector on it. The rotor are filled with alphabet. The spindle has an setting line. (refer to the DIY Enigma machine)
How It Works? The Basic Idea (7) The variance 1. Three rotor can be put in any order. 2. Each rotor can start with any character. 3. Each notch can be replaced.
Classes Structure EnigmaMachine RotorReflector
Class EnigmaMachine Data Member: Rotor r1, r2, r3 Reflector r Member Function: Check and rotate Input and output Setting the arrangement of the three rotor
Class Rotor Data Member: char charArray int notchLocation int startingPoint Member function: Rotate Set notch location Set starting point Mapping Input and output
Class Reflector Data member Member function Input and Output mapping
Control flow - EnigmaMachine Read a character process Return a character Check and rotate
Control flow – Rotor / Reflector InputMapping Output
Control Flow – Check and Rotate Check rotor r1, get notch position Check rotor r2, get notch position Check rotor r3, get notch position Rotate depends on condition
How To Test? Test Plan For the entire class EnigmaMachine, use it to encrypt an entire passage, then decrypt it. Develop code breaking programs for the Caesar cipher, Substitute cipher, Rotating cipher, and try them on the code encrypt by Enigma machine.
Some Features can be Added Replace the 26 alphabets and a space with ASCII table Graphical user interface design Upgrade to 4-rotor Enigma machine