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.