This book constitutes the refereed proceedings of the 4th International Conference on
Principles of Security and Trust POST 2015 held as part of the European Joint Conferences on
Theory and Practice of Software ETAPS 2015 London UK in April 2015. The 17 regular papers
presented in this volume were carefully reviewed and selected from 57 submissions. In addition
one invited talk is included. The papers have been organized in topical sections on information
flow and security types risk assessment and security policies protocols hardware and
physical security and privacy and voting.
