Vernam's Patent
The combining function Vernam specified in U.S. Patent 1,310,719, issued July 22, 1919, is the XOR operation, applied to the individual impulses or bits used to encode the characters in the Baudot code. Vernam did not use the term "XOR" in the patent, but he implemented that operation in relay logic. In the example Vernam gave, the plaintext is A, encoded as "++---" in Baudot, and the key character is B, encoded as "+--++". The resulting ciphertext will be "-+-++", which encodes a G. Combining the G with the key character B at the receiving end produces "++---", which is the original plaintext A. The NSA has called this patent "perhaps one of the most important in the history of cryptography.".
Read more about this topic: Gilbert Vernam
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