Rotor Ciphers

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.
  

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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

• http//www.burningwell.org/gallery2/d/2974-2/tteni
  gma4.jpg
• http//cleavebooks.co.uk/trol/trolc07.pdf
• http//en.wikipedia.org/wiki/Cryptanalysis_of_the_
  Enigma
• http//en.wikipedia.org/wiki/Rotor_machine
• http//en.wikipedia.org/wiki/Enigma_machine