Here are some books with good information on Encryption/Cryptography:
Cryptography: Theory and Practice - Douglas R. Stinson's Cryptography: Theory and Practice is a mathematically intensive examination of cryptography, including ciphers, the Data Encryption Standard (DES), public key cryptography, one-way hash functions, and digital signatures. Stinson's explication of "zero- sum proofs"--a process by which one person lets another person know that he or she has a password without actually revealing any information--is especially good.
SSH, The Secure Shell: The Definitive Guide - You can't go wrong with thisO'Rielly book - and this one is a mustall Unix users/admins as SSH quickly becomes a popular choice for securing remote transfers and connections.
Handbook of Applied Cryptography - A hefty handbook for both novices and experts, introducing practical aspects of conventional and public-key cryptography and offering information on the latest techniques and algorithms in the field. Mathematical treatments accompany practical discussions of areas including pseudorandom bits and sequences, stream and block ciphers, hash functions, and digital signatures.
The Internet has thousands of encryption/cryptography related resources. Here are a few that cover a broad range of topics:
Radius.net Software Archive - Your one stop shop for any and all encryption related software.
Phil Zimmermann's Homepage - The creator of PGP and a cryptography pioneer.
PGP Distribution site - MIT Distribution Center for PGP (Pretty Good Privacy).
Hushmail - Web based email with strong encryption.
AES - Information on AES (Advanced Encryption Standard) from NIST.
Cryptographic Toolkit - NIST's cryptography standard.
Encryption and Linux - The Linux Encryption-HOWTO Homepage.
Cipher - IEEE security and privacy newsletter.
C.R.I.S. - The Cryptography and Information Security Research Laboratory.
Encryption in the workplace - How electronic encryption works and how it will change your business.
Beginner's guide to Cryptography - Some useful resources and info.
U.S. Encryption Export Control Regulations - As published in January 2000.