This book constitutes the proceedings of the Second International Conference on Frontiers in Cyber Security, FCS 2019, held in Xi'an, China, in November 2019. The 20 full papers along with the 2 short papers presented were carefully reviewed and selected from 67 submissions. The papers are organized in topical sections on: symmetric key cryptography; public key cryptography; post-quantum cryptography: signature; attack and behavior detection; authenticated key agreement; blockchain; system and network security.