Rotor Machine

Updated 12 Aug 2026

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Definition
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  an electromechanical cipher device from the early-to-mid 20th century that automates substitution ciphers using rotating discs ("rotors"), each encoding a substitution table that shifts by one position with every keystroke
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Hebern machine (single rotor)
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  the secret key is the disc's initial position; each keystroke both encrypts a letter and rotates the disc by one notch, so the same input letter maps to a different output letter each time it's pressed
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Enigma (multiple rotors)
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  used 3–5 rotors; the key is the rotors' initial settings — with 3 rotors, the key space is $26^3 = 2^{18}$ , brute-forceable on a modern computer in seconds
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  broken via ciphertext-only attacks by British cryptographers at Bletchley Park during WWII, a major factor in several wartime battles
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Why they eventually broke
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  despite growing more complex to resist frequency analysis, rotor machines were still vulnerable to statistical (letter/digram/trigram frequency) attacks, the same fundamental weakness as the Substitution Cipher
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Related
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  Substitution Cipher

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