Introductory textbook on Cryptography.Cryptography plays a crucial role in many aspects of today's world, from internet banking and ecommerce to email and web-based business processes. This book combines an informal style with rigorous proofs of the key results to give an accessible introduction. It comes with plenty of examples and exercises (many with hints and solutions), and is based on a highly successful course developed and taught over many years to undergraduate and graduate students in mathematics and computer science.Cryptography plays a crucial role in many aspects of today's world, from internet banking and ecommerce to email and web-based business processes. This book combines an informal style with rigorous proofs of the key results to give an accessible introduction. It comes with plenty of examples and exercises (many with hints and solutions), and is based on a highly successful course developed and taught over many years to undergraduate and graduate students in mathematics and computer science.Cryptography plays a crucial role in many aspects of today's world, from internet banking and ecommerce to email and web-based business processes. Understanding the principles on which it is based is an important topic that requires a knowledge of both computational complexity and a range of topics in pure mathematics. This book provides that knowledge, combining an informal style with strong proofs of the key results to provide an accessible introduction. It includes many examples and exercises, and is based on a highly successful course developed and taught over many years.1. Basics of cryptography; 2. Complexity theory; 3. Non-deterministic computation; 4. Probabilistic computation; 5. Symmetric cryptosystems; 6. One-way functions; 7. Public key cryptography; 8. Digital signatures; 9. Key establishment protocols; 10. Secure encryption; 11. Identification schemes; Appendix 1; Appendix 2; Appendix 3; Appendix 4; Appendix 5; Appendix 6; Bibliography; Indel£Ã