Communication Theory of Secrecy Systems (1945 – 1949)

Claude Shannon's report, originally issued as a classified document entitled A Mathematical Theory of Cryptography, Memorandum MM 45-110-02, September 1, 1945,  was formally published as "Communication Theory of Secrecy Systems" in Bell System Technical Journal, 28(4), 656–715.  This paper, discussing cryptography from the viewpoint of information theory, contained a proof that all theoretically unbreakable ciphers must have the same requirements as the one-time pad.