Enigma Cipher

The Enigma Cipher was invented by Arthur Scherbius in 1918 and later adapted for military use by Germany in the 1920s and 1930s. Unlike simple substitution systems such as the Simple Substitution Cipher, Enigma implemented a continuously changing polyalphabetic substitution. Each keypress rotated internal components, meaning the same letter could encrypt differently each time it appeared.

The machine consisted of rotating rotors (each with scrambled internal wiring), a reflector that sent the signal back through the rotors along a new path, and a plugboard that swapped letter pairs before and after rotor processing. The combination of rotor order, ring settings, starting positions, and plugboard connections determined the encryption output.

Enigma Cipher: Configuration

The following configuration produces the example output shown below:

Plugboard:                  (none)
Rotor Order (Left → Right): III   I  II
Ring Settings:                6   3   1
Starting Positions:           C   A   T

Because rotor stepping alters the wiring path after every keypress, even repeated letters will encrypt differently.

Enigma Cipher: Encoding Example

With the above configuration loaded, encrypting the plaintext “HELLO” produces:

Plaintext:  H  E  L  L  O
Ciphertext: V  D  H  P  Q

Notice that the two “L” characters encrypt to different letters (“H” and “P”). This happens because the rightmost rotor advances after each keypress, shifting the substitution pattern dynamically.

Enigma Cipher: Decoding

Enigma encryption is symmetric. Resetting the machine to the same rotor order, ring settings, and starting positions (III I II with CAT and rings 6-3-1), typing “VDHPQ” will yield:

Input:  V  D  H  P  Q
Output: H  E  L  L  O

No separate decryption algorithm is required — the reflector design ensures the same mechanical process performs both encryption and decryption.

Enigma Cipher: Notes

Though once believed to be unbreakable, Enigma was successfully broken during World War II through a combination of Polish mathematical breakthroughs and large-scale cryptanalysis efforts at Bletchley Park. The work done there not only influenced the outcome of the war but also helped lay foundations for modern computing and cryptography.