The aim of this book is to understand: Introduction to the Concepts of Security: the need for security, Security Approaches, Principles of Security, Types of Attacks. Cryptographic Techniques: Plain Text and Cipher Text, Substitution Techniques, Transposition Techniques, Encryption and Decryption, Symmetric and Asymmetric Key Cryptography, Key Range and Key Size, Possible Types of Attacks. Computer-based Symmetric Key Cryptographic Algorithms: Algorithm Types and Modes, an overview of Symmetric Key Cryptography, DES, International Data Encryption Algorithm (IDEA), RC 5, Blow-fish, AES, Differential and Linear Crypt-analysis.