Comment Historically... (Score -1) 238
Cryptography is a long series of people reinventing schemes because A: they didn't know about them (the secrecy of the existence was maintained), and B: it was effective. A great example is the Jefferson disk (1795) and Bazeries Cylinder (US-Army M-94, 1923-1942), which were functionally identical.
http://en.wikipedia.org/wiki/Jefferson_disk
http://en.wikipedia.org/wiki/M-94