The textbook introduces various areas of cryptography to undergraduate and graduate students in mathematics and computer science. It covers classical cryptosystems, Shannon's approach to perfect secrecy, block ciphers and hash functions. Public-key cryptography, signature schemes and pseudo random number generators are also discussed in detail. Other chapters discuss key distribution and entity authentication. The book is geared toward serving as a class-room textbook with numerous solved examples and exercises. It genuinely deserves its reputation as an indispensable textbook for cryptography teaching.