New York: Bell Telephone Laboratories / American Telephone and Telegraph Company 1949. First Edition. -753 pages. 8vo. Original blue printed wrappers. With the stamp "Property of the Telephone Systems Training Section" in several places, including wrappers and several pages internally. Spine slanted, minor sunning to the extremities, some foxing to first page. The entire October 1949 issue of the Bell System Technical Journal, with the article by Claude Shannon on pp. 656-715. Very Good. Wraps. 
"The discoverer of information theory examines cryptology [ cryptography ] in the terms of that theory: redundancy, entropy, equivocation. Shannon develops formulas that enable the cryptanalyst to tell when a solution in a particular cipher system is valid. He discusses perfect secrecy (absolutely unbreakable cipher) and ideal secrecy (practically unbreakable ciphers) and work characteristics needed to solve different kinds of cipher...." Secret Writings: Selected Works on Modern Cryptology, p324-5
Claude Shannon was an American mathematician perhaps best known as the founder of the field of information theory. Shannon showed the theoretical and practical foundation for digital circuits (1938), the mathematical foundation for the internet (1948) and this paper, a foundational work in Cryptography. Shannon even wrote a paper on computer chess. For the work in this paper, Shannon was appointed ''as a consultant on cryptographic matters to the United States Government'' (Elwood, Shannon Collected Papers, p. xiii) The work presented in this paper appeared originally in a confidential report ''A Mathematical Theory of Cryptography'' dated Sept 1, 1945 but was classified at the time due to World War II.
Schulman, An Annotated Bibliography of Cryptography, p122, noting "Theoretical and mathematical aspects of ciphers." Not in Galland. See also Kahn, The Code Breakers for a discussion of this paper and Shannon's impact.