Evolution of Information Security Algorithms

The chapter begins with the classical encryption techniques namely substitution cipher and transposition cipher. It covers popular substitution ciphers like Caesar, mono-alphabetic, Playfair, poly-alphabetic, and vignere cipher. Transposition-based ciphers like Rail Fence and Simple Columnar are also discussed with example. Modern security algorithms, designed using both substitution and transposition based approaches, are categorized as stream cipher and block cipher. The chapter explores popular stream cipher algorithms like one-time pad (Vernam cipher), RC4, and A5/1. The key concepts of block cipher algorithms like key expansion method, Shannon's theory of confusion and diffusion, and the basic Feistel structure are covered elegantly. Later, the chapter covers block cipher algorithms like DES, 3DES, IDEA, Blowfish, and CAST-128 and analyzes them with respect to their key generation methods, S-box designs, and vulnerabilities, etc.