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300px Johannes Trithemius' Polygraphiae (1518) — the first printed book on cryptology. Books on cryptography have been published sporadically, and with highly variable quality, for a long time. This despite the tempting, though superficial, paradox that secrecy is of the essence in sending confidential messages — see Kerckhoffs' law.
In contrast, the revolution in cryptography and secure communications of the last 25 years is well covered in the available literature. Things have improved.
An early example of a book about cryptography was a Roman work, now lost and known only by references. Later, various authors wrote (variously responsibly) on cryptography. Many of the early works were esoteric, mystical, and reputation-promoting; cryptography being mysterious, there was much opportunity for such things. At least one work by Trithemius was put on the Index (ie, banned) by the Catholic Church as being about black magic or witchcraft. Many writers claimed to have invented unbreakable cyphers. None were, though it sometimes took a long while to establish this.
In the 19th century, the general standard improved somewhat (eg, works by Auguste Kerckhoffs, Friedrich Kasiski, and Étienne Bazeries). Colonel Parker Hitt and William Friedman in the early 20th century also wrote books on cryptography. These authors, and others, mostly abandoned the mystical/magical tone.
With the mechanization of armies and the invention and use of radio, communications (especially military communications) went wireless and some means of protecting messages -- which were necessarily heard by all who bothered to listen -- became immediately imperative. Thus, about the time of WWI, cryptography became not merely a useful technique in diplomacy, espionage, and military operations, but really important. By the end of WWI, cryptography and its literature began to be both 'official', and 'classified'.
Thereupon, publicly available material started to diverge more than before from actual cryptographic, and cryptanalytic, practice, largely by 'leaving things out'. There began a period in which public descriptions of cryptography were either intended for children, deliberately misleading, or limited to historical issues. Some, such as The American Black Chamber by Herbert Yardley were mixtures of everything, including a return to the personal reputation puffery of the Renaissance, and more than a little magical gee whiz.
Until the late twentieth century 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 60s) 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.
There are now many books available on cryptography; this is mostly a modern phenomenon. Much information that was top secret a half century ago is now available to the public. Principles and techniques of major parts of contemporary cypher design have also in many cases been published.
The divergence between official knowledge and practice and public knowledge continues; cryptography is still important. Such organizations as NSA and GCHQ pretty much don't talk to anyone. Some publicly working cryptographers believe that the gap between the official (and secret) 'state of the art', and the publicly known, has decreased very substantially since 1976. Others are less sure. Readers should be aware of the possibility that cryptographic practice in official circles may be quite different and possibly far advanced over that available in the public literature. Or maybe not.
And the unsavory side of cryptographic literature also continues. Many books from the earlier era are still in circulation, confusing readers needlessly. The warning at the end of the article on cryptography should be taken seriously; there is still much nonsense in published accounts of cryptography, and the quality of information available on line is wildly variable.