Introduction to Cryptography with Coding Theory is a very math-heavy, but excellent and readable text on Cryptography.

As compared to the standard text, Applied Cryptography by Bruce Schneier, ItCwCT is very light on implementation details and code examples, and much heavier on the fundamental mathematical basis for various encryption schemes.

Normally a book that skews this heavy toward the theory is one I won't like, but ItCwCT avoids the mistake of many other theoretical textbooks by providing many examples of applying the theory (it just does so in terms of math, not code), and is extremely readable and well paced. Very rarely did I feel confused by the text, and overall I think the ideas are presented very well.

ItCwCT is wider in scope than Schneier's book as well. Applied Cryptography deals with the basics of cryptosystems such as DES and RSA, then gets right into implementations and source code. ItCwCT establishes the foundational basis of the text early on with a primer on essential number theory, talks about some simple cryptosystems such as substitution ciphers and block ciphers, then goes deep on topics like AES, DES, RSA, Signatures, Digital Cash, Secret Sharing, Games, Key exchanging, Information Theory, Elliptic Curve Cryptosystems (not covered at all in Applied Cryptography), Error Correction Codes, and Quantum Cryptography. Most of these topics get a brief mention, if any at all, in Schneier's book, and ItCwCT goes very deep in all of these topics.

I think Applied Cryptography works well as an introduction to cryptography, maybe for Undergrads, but ItCwCT works much better as an advanced, graduate text, while remaining readable and understandable even for undergrads.