Anonymity and Covert Channels in Simple Timed Mix-Firewalls -- Practical Traffic Analysis: Extending and Resisting Statistical Disclosure -- The Traffic Analysis of Continuous-Time Mixes -- Reputable Mix Networks -- Secure Outsourcing of Sequence Comparisons -- An Improved Construction for Universal Re-encryption -- Electromagnetic Eavesdropping Risks of Flat-Panel Displays -- On the Anonymity of Banknotes -- FLASCHE – A Mechanism Providing Anonymity for Mobile Users -- Cryptographically Protected Prefixes for Location Privacy in IPv6 -- Protecting User Data in Ubiquitous Computing: Towards Trustworthy Environments -- Synchronous Batching: From Cascades to Free Routes -- On Flow Correlation Attacks and Countermeasures in Mix Networks -- Measuring Anonymity in a Non-adaptive, Real-Time System -- Panel Discussion — Mix Cascades Versus Peer-to-Peer: Is One Concept Superior? -- On the PET Workshop Panel “Mix Cascades Versus Peer-to-Peer: Is One Concept Superior?” -- A Formal Privacy System and Its Application to Location Based Services -- Privacy-Preserving Trust Negotiations -- Language-Based Enforcement of Privacy Policies -- Searching for Privacy: Design and Implementation of a P3P-Enabled Search Engine -- Contextualized Communication of Privacy Practices and Personalization Benefits: Impacts on Users’ Data Sharing and Purchase Behavior -- Panel Discussion — Conforming Technology to Policy: The Problems of Electronic Health Records.

This book constitutes the thoroughly refereed post-proceedings of the 4th International Workshop on Privacy Enhancing Technologies, PET 2004, held in Toronto, Canada in May 2004. The 20 revised full papers presented were carefully selected from 68 submissions during two rounds of reviewing and improvement. Among the topics addressed are mix networks, mix firewalls, traffic analysis, sequence analysis, re-encryption, electromagnetic eavesdropping, anonymity of banknotes, IPv6, trustworthy environments, flow correlation attacks, anonymity measuring, mix cascades, trust negotiation, privacy policies, and personalization.