Bibliography:Cryptography

Elementary

 * Gaines, Helen F. Cryptanalysis
 * Sinkov, Abraham. Elementary Cryptanalysis: A Mathematical Approach Excellent; readable at a high school level
 * The Codebreakers by David Kahn. the classic history of the field, Ancient Egypt to 20th Century
 * The Code Book by Simon Singh, a clearly written anecdotal history of crypto, covering modern methods including public key.
 * Crypto: How the Code Rebels Beat the Government Saving Privacy in the Digital Age by Steven Levy, about the political and legal conflicts in the US about cryptography, such as the Clipper Chip controversy and the Bernstein v. United States lawsuit.
 * Stealing Secrets, Telling Lies: How Spies and Codebreakers Helped Shape the Twentieth Century, by James Gannon.
 * sci.crypt mini-FAQ.
 * NSA's CryptoKids.
 * RSA Laboratories' Frequently Asked Questions About Today's Cryptography
 * Cryptography: The Ancient Art of Secret Messages by Monica Pawlan - February 1998
 * In Code: A Mathematical Journey by Sarah Flannery (with David Flannery). Popular account of Sarah's award-winning project on public-key cryptography, co-written with her father.

More advanced, but dated

 * Friedman, William F. Military Cryptanalysis

Definitely mathematical

 * Applied Cryptography: Protocols, Algorithms, and Source Code in C, by Bruce Schneier &mdash; a common reference for programmers
 * Handbook of Applied Cryptography by A. J. Menezes, P. C. van Oorschot, and S. A. Vanstone, somewhat more mathematical than Schneier's book. PDF download
 * Introduction to Modern Cryptography by Phillip Rogaway and Mihir Bellare, a mathematical introduction to theoretical cryptography including reduction-based security proofs.  PDF download.

Difficulties of cryptography
Well-known papers:
 * "Why Cryptosystems Fail", Ross Anderson HTML
 * "Why Cryptography Is Harder Than It Looks", Bruce Schneier HTML
 * "Lessons Learned in Implementing and Deploying Crypto Software", Peter Gutmann PDF
 * "Why Johnny can't encrypt: a usability evaluation of PGP 5.0", Alma Whitten & J.D. Tygar PDF

Ross Anderson's book Security Engineering provides more detailed coverage. The entire first edition and parts of the second are available online. index page

Fiction

 * Cryptonomicon by Neal Stephenson (novel, WW2 Enigma cryptanalysis figures into the story, though not always realistically).
 * Alvin's Secret Code by Clifford B. Hicks (children's novel that introduces some basic cryptography and cryptanalysis).
 * Cryptography and Mathematics by Bernhard Esslinger, 200 pages, part of the free open-source package Cryptool, http://www.cryptool.com.