Book excerpt: This book constitutes the refereed proceedings of the 18th International Conference on Cryptology in India, INDOCRYPT 2017, held in Chennai, India, in December 2017. The 19 revised full papers presented in this book were carefully reviewed and selected from 75 submissions. The focus of the conference includes works on Public-Key Cryptography, Cryptographic Protocols, Side-Channel Attacks, Implementation of Cryptographic Schemes, Functional Encryption, Symmetric-Key Cryptanalysis, Foundations, and New Cryptographic Constructions.