Book excerpt: This book constitutes the refereed proceedings of the 6th International Conference on Cryptology in India, INDOCRYPT 2005, held in Bangalore, India in December 2005. The 31 revised full papers presented together with 1 invited paper were carefully reviewed and selected from 148 submissions. The papers are organized in topical sections on sequences, boolean function and S-box, hash functions, design principles, cryptanalysis, time memory trade-off, new constructions, pairings, signatures, applications, e-cash, and implementations.