This book constitutes the refereed proceedings of the 11th International Conference on Provable Security, ProvSec 2017, held in Xi'an, China, in October 2017. The 24 full papers and 5 short papers presented were carefully reviewed and selected from 76 submissions. The papers are grouped in topical sections on secure cloud storage and computing; digital signature and authentication; authenticated encryption and key exchange; security models; lattice and post-quantum cryptography; public key encryption and signcryption; proxy re-encryption and functional encryption; protocols.  .