Garrett, Paul: Making, Breaking Codes

For courses in Cryptography, Cryptology, and Applications of Number Theory and Abstract Algebra.This is the only undergraduate text to explain fundamental ideas of classical and modern cryptography, and provide the essential background in number theory, abstract algebra, and probability-with surveys of relevant parts of complexity theory. A level of linear algebra sophistication is assumed in the reader. A user-friendly, down-to-earth tone gives students concretely motivated introductions to all topics.