1. Rotor Ciphers

2. History Invented in 1915 by Theo A. van Hengel and R. P. C. Spengler
Edward Hugh Hebem developed a rotor machine in the United States in 1917.
Arthur Sherbius designed the Engima machine.
Marian Rejewski broke the Enigma machine in 1932.

3. Mechanization Rotors have 26 positions. Multiple rotors per machine
User enters a character
Electrical current goes through rotor
Rotor rotates
Next time same character is pressed, different cipher character is produced

4. Mechanization Key is pressed Current goes through rotor
Cipher character lightbulb lights up
Rotor rotates
Reflector (only in Enigma) made decryption the same as encryption, but was flawed

5. Mechanization (Decryption)
To decrypt, the user must know:
Wheel order – The choice of rotors and their order
Initial position of the rotors – Chosen by operator, changed for each message
Ring settings – Position of the alphabet ring relative to the rotor wiring (shift cipher)
Plug settings - Connections of plugs in plugboard (plugboard connects pairs of letters and switches them before and after main rotor)

6. Mechanization (Decryption)
To decrypt, the rotors were taken out and turned around from the encryption position to reverse the circuitry.
This was not necessary in the Enigma because of the reflector.

7. Cryptanalysis
The unsteckered Enigma (without plugboard) was easily broken.
The Polish discovered that they keyboard was arranged ABCDEF, as opposed to QWERTY.
A French spy provided information to the Polish that allowed them to create a replica Enigma machine.
The Polish broke the Enigma machine in 1932 through algebra.

8. Cryptanalysis The reflector was a flaw in Enigma machines.
The Polish invented a device known as a cryptologic bomb, which was essentially six Enigma machines.
The Germans constantly made more complex Enigma machines (such as the Kriegsmarine Enigma).

9. Bibliography