The VIC cipher was a pencil and paper cipher used by the Soviet spy Reino Häyhänen, codenamed "VICTOR".
It was arguably the most complex hand-operated cipher ever seen, when it was first discovered. The initial analysis done by the NSA in 1953 did not absolutely conclude that it was a hand cipher, but its placement in a hollowed out 5c coin implied it could be broken by pencil and paper. The VIC cipher remained unbroken until more information about its structure was available.
Although certainly not as complex or secure as modern computer operated stream ciphers or block ciphers, in practice messages protected by it resisted all attempts at cryptanalysis by at least NSA from its discovery in 1953 until Häyhänen's defection in 1957.
Read more about VIC Cipher: A Revolutionary Leap, History
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