The chapter "Classical Cryptography" from the book "Cryptography Theory and Practice, Third Edition" by Douglas R. Stinson covers various classical cryptosystems and their cryptanalysis. It begins with an introduction to simple cryptosystems such as the Shift Cipher, Substitution Cipher, Affine Cipher, Vigenère Cipher, Hill Cipher, Permutation Cipher, and Stream Ciphers. Each system is followed by a section on cryptanalysis, detailing how to break these ciphers. The chapter also includes notes and exercises for further exploration. Subsequent chapters delve into more advanced topics in cryptography, including Shannon’s theory, block ciphers and the Advanced Encryption Standard (AES), cryptographic hash functions, public-key cryptography, signature schemes, pseudo-random number generation, identification schemes, key distribution, key agreement schemes, public-key infrastructure (PKI), secret sharing schemes, and multicast security and copyright protection. Each section provides a comprehensive overview of the concepts, algorithms, and security analyses, along with practical examples and exercises to reinforce understanding.The chapter "Classical Cryptography" from the book "Cryptography Theory and Practice, Third Edition" by Douglas R. Stinson covers various classical cryptosystems and their cryptanalysis. It begins with an introduction to simple cryptosystems such as the Shift Cipher, Substitution Cipher, Affine Cipher, Vigenère Cipher, Hill Cipher, Permutation Cipher, and Stream Ciphers. Each system is followed by a section on cryptanalysis, detailing how to break these ciphers. The chapter also includes notes and exercises for further exploration. Subsequent chapters delve into more advanced topics in cryptography, including Shannon’s theory, block ciphers and the Advanced Encryption Standard (AES), cryptographic hash functions, public-key cryptography, signature schemes, pseudo-random number generation, identification schemes, key distribution, key agreement schemes, public-key infrastructure (PKI), secret sharing schemes, and multicast security and copyright protection. Each section provides a comprehensive overview of the concepts, algorithms, and security analyses, along with practical examples and exercises to reinforce understanding.