Existence and Nonexitence of strongly regular graphs , maintained by Andries E. Brouwer.
Database of two-weight codes , maintained by Eric Chen.
Bounds on the parameters of various types of codes , maintained by Markus Grassl.
Ronald L. Rivest : Cryptography and Security
Lecture Notes on Cryptography. This 289-page online book is a useful technical reference.. By S. Goldwasser and M. Bellare.
Introduction to Modern Cryptography. Another useful and lengthy set of lecture notes. By Mihir Bellare and Phillip Rogaway.