This book constitutes the refereed post-conference proceedings of the 28th International Workshop on Security Protocols, held in Cambridge, UK, during March 27–28, 2023.Thirteen papers out of 23 submissions were selected for publication in this book, presented together with the respective transcripts of discussions.

Sleepwalking into Disaster? Requirements Engineering for Digital Cash.- Transporting a Secret Using Destructively-Read Memory.- Authentication of IT Professionals in the Wild - A Survey.- Incentives and Censorship Resistance for Mixnets Revisited.- Can’t Keep them Away: The Failures of Anti-Stalking Protocols in Personal Item Tracking Devices.- Who is Benefiting from Your Fitness Data? A Privacy Analysis of Smartwatches.- Trusted Introductions for Secure Messaging.- Choosing Your Friends: Shaping Ethical Use of Anonymity Networks.- One Protocol to Rule them All? On Securing Interoperable Messaging.- If it’s Provably Secure, it Probably isn’t: Why Learning from Proof Failure is Hard.- Towards Human-Centric Endpoint Security.- Determining an Economic Value of High Assurance for Commodity Software Security.- Blind Auditing and Probabilistic Access Controls.