The System Likes You -- Experiences with Host-to-Host IPsec -- Experiences with Host-to-Host IPsec -- Repairing the Bluetooth Pairing Protocol -- Repairing the Bluetooth Pairing Protocol -- Keep on Blockin' in the Free World: Personal Access Control for Low-Cost RFID Tags -- Keep on Blockin' in the Free World -- PIN (and Chip) or Signature: Beating the Cheating? -- PIN (and Chip) or Signature: Beating the Cheating? -- Insecure Real-World Authentication Protocols (or Why Phishing Is So Profitable) -- Insecure Real-World Authentication Protocols (or Why Phishing Is So Profitable) -- Authorisation Subterfuge by Delegation in Decentralised Networks -- Authorisation Subterfuge by Delegation in Decentralised Networks -- Multi-channel Protocols -- Multi-channel Protocols -- Combining Crypto with Biometrics: A New Human-Security Interface -- User-Friendly Grid Security Architecture and Protocols -- User-Friendly Grid Security Architecture and Protocols -- Countering Automated Exploits with System Security CAPTCHAS -- Countering Automated Exploits with System Security CAPTCHAS -- The System Likes You? -- Enhancing Privacy with Shared Pseudo Random Sequences -- Enhancing Privacy with Shared Pseudo Random Sequences -- Non-repudiation and the Metaphysics of Presence -- Non-repudiation and the Metaphysics of Presence -- Understanding Why Some Network Protocols Are User-Unfriendly -- Understanding Why Some Network Protocols Are User-Unfriendly -- Community-Centric Vanilla-Rollback Access, or: How I Stopped Worrying and Learned to Love My Computer -- Community-Centric Vanilla-Rollback Access, or: How I Stopped Worrying and Learned to Love My Computer -- Listen Too Closely and You May Be Confused -- Listen Too Closely and You May Be Confused -- The Dining Freemasons (Security Protocols for Secret Societies).-The Dining Freemasons (Security Protocols for Secret Societies) -- On the Evolution of Adversary Models in Security Protocols (or Know Your Friend and Foe Alike) -- Safer Scripting Through Precompilation -- Safer Scripting Through Precompilation -- Implementing a Multi-hat PDA -- Implementing a Multi-hat PDA -- Anonymous Context Based Role Activation Mechanism -- Anonymous Context Based Role Activation Mechanism -- Topology of Covert Conflict -- The Initial Costs and Maintenance Costs of Protocols -- The Initial Costs and Maintenance Costs of Protocols -- Alice and Bob.

Welcome to the Proceedings of the 13th International Security Protocols Wo- shop. As usual, our meeting in Cambridge was just the beginning. After that, position papers were revised (often more than once) and transcripts were c- culated, discussed, and edited several times: our intention was not to produce a sterile record of who said what, but to share some promising lines of enquiry into interesting problems. Now we bring these proceedings to a wider audience so that you can join in. Our theme this time was "The systemlikes youandwants to be yourfriend." Security is usually seen as making systems more di?cult for humans to use. Might there be advantages to looking at security in the context of more general design problems? Perhaps those investigating the general properties of system design and those of us in the security community have more to say to each other than we thought. Our thanks to Sidney Sussex CollegeCambridgefor the use of their facilities, and to the University of Hertfordshire for lending us several of their sta?. Particular thanks to Johanna Hunt of the University of Hertfordshire for being our impresario and organizing everything, and to Lori Klimaszewska of the University of CambridgeComputing Service for transcribing the audio tapes (in which the "crash barriers" nearly prevented collisions). The Security Protocols Workshop exists because you, the audience, part- ipate. Once you have dived into these proceedings and have had some Eleatic thoughts, we expect to hear from you.