VIC cipher

The VIC cipher was a pencil and paper cipher used by the Soviet spy Reino Häyhänen, codenamed VICTOR, in the 1950s. By general classification it belongs to the Nihilist family of ciphers, and it combines several components: digit-wise addition modulo 10 known as chain addition, a lagged Fibonacci generator that stretches a short digit sequence, a straddling checkerboard that turns letters into digits, and a disrupted double transposition. The secret key was a phrase of at least twenty letters, a date, a personal number unique to the agent and a five digit keygroup that was embedded in the ciphertext. When it was found inside a hollowed out nickel, later known as the Hollow Nickel Case, the cipher resisted analysis by the American National Security Agency from 1953 until Häyhänen defected in 1957, and it was arguably the most complex hand operated cipher ever seen at that time.