From the end of World War II until the early 1980s most aspects of modern cryptography were regarded as the special concern of governments and the military, and were protected by custom and, in some cases, by statute. The most significant work to be published on cryptography in this period is undoubtedly David Kahn's The Codebreakers, which was published at a time (mid-1960s) when virtually no information on the modern practice of cryptography was available. Kahn has said that over ninety percent of its content was previously unpublished. The book caused serious concern at the NSA despite its lack of coverage of specific modern cryptographic practice, so much so that after failing to prevent the book being published, NSA staff were informed to not even acknowledge the existence of the book if asked. In the US military, mere possession of a copy by cryptographic personnel was grounds for some considerable suspicion. Perhaps the single greatest importance of the book was the impact it had on the next generation of cryptographers. Whitfield Diffie has made comments in interviews about the effect it had on him.
Read more about this topic: Books On Cryptography