Besides oral conversations and written language many other ways of information-transport are known: like the bush telegraph, drums, smoke signals etc. Those methods are not cryptography, still they need en- and decoding, which means that the history of language, the history of communication and the history of cryptography are closely connected to each other
The timeline gives an insight into the endless fight between enciphering and deciphering. The reasons for them can be found in public and private issues at the same time, though mostly connected to military maneuvers and/or political tasks.
One of the most important researchers on Cryptography through the centuries is
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David Kahn can be considered one of the most important historians on cryptography. His book The Codebreakers. The comprehensive history of secret Communication from Ancient Times to the Internet, written in 1996 is supposed to be the most important work on the history of cryptography.