This book constitutes the refereed proceedings of 5 workshops held at the 21st International Conference on Financial Cryptography and Data Security, FC 2017, in Sliema, Malta, in April 2017.

The 39 full papers presented were carefully reviewed and selected from 96 submissions. They feature the outcome of the 5th Workshop on Encrypted Computing and Applied Homomorphic Cryptography, WAHC 2017, the 4th Workshop on Bitcoin and Blockchain Research, BITCOIN 2017, the Second Workshop on Secure Voting Systems, VOTING 2017, the First Workshop on Trusted Smart Contracts, WTSC 2017, and the First Workshop on Targeted Attacks, TA 2017.

The papers are grouped in topical sections named: encrypted computing and applied homomorphic cryptography; bitcoin and blockchain research; advances in secure electronic voting schemes; trusted smart contracts; targeted attacks.