For a broad introduction to information theory, coding, and their applications in cryptography, I reccommend _Codes_and_Cryptgraphy_ by Dominic Welsh (Oxford Science Publications, ISBN 0-19-853288-1 and ISBN 0-19-853287-3 Pbk). Some topics: information theory, noiseless coding theory, noisy channels, error-correcting codes, source theory, natural language structure, one-time pads, computational complexity, public key systems (RSA, Knapsacks, Rabin, Elgamal), authentication and digital signatures (Diffie-Lamport, Rabin), Diffie-Helman key exchange, and random numbers and random cryptsstems. -Thomas