Nice intro to a very complex field.
I particularly enjoyed your timeline image.
Another further reading book I would add for those who love details is
Making, Breaking CODES: An Introduction to Cryptology. ISBN 0-13-030369-0
http://vig.prenhall.com/catalog/academic/product/0,1144,0130303690,00.html
Another good book like the The Code Book mention in an earlier post is:
Crypto: How the Code Rebels Beat the Government Saving Privacy in the Digital Age.
I find it goes into more details about the break through of Asymmetric Encryption how its relevant to the key distribution problem.