Books on cryptography
Books on cryptography have been published sporadically and with highly variable quality for a long time. This is despite the tempting, though superficial, paradox that secrecy is of the essence in sending confidential messages — see Kerckhoffs' principle. In contrast, the revolutions in cryptography and secure communications since the 1970s are well covered in the available literature. Early history An early example of a book about cryptography was a Roman work, now lost and known only by references. Many early cryptographic works were esoteric, mystical, and/or reputation-promoting; cryptography being mysterious, there was much opportunity for such things. At least one work by Trithemius was banned by the Catholic Church and put on the Index Librorum Prohibitorum as being about black magic or witchcraft. Many writers claimed to have invented unbreakable ciphers. None were, though it sometimes took a long while to establish this. In the 19th century, the general standard improved somewhat (e.g., 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 any mystical or magical tone. Open literature versus classified literature With the invention of radio, much