Cryptographic privacy enhancing technologies

The growth of information and communication technology creates difficulties for individuals to monitor and control their private information which can be copied, transferred from one location to another within a second and accessible to many people. This thesis focuses on a number of cryptographic technologies, which have been introduced and developed to protect user privacy, including anonymous signatures, anonymous authentication, anonymous credentials and anonymous routing. Our contributions to these technologies are in three aspects: more efficiency, more security and better functionality. We identify and formalize new security requirements, and improve and build formal security models for a number of privacy-preserving primitives. We construct new anonymous routing systems whose security relies on complexity assumptions different from those of previous systems. We propose several anonymous signature schemes with constant computation costs, very short signatures and keys and compact system parameters that can be shared by multiple groups. These schemes can be converted into anonymous authentication schemes and used as building blocks for anonymous credential systems. Our systems provide diversified properties, such as anonymity revocability, ad-hoc group formation, signature traceability, identity-based and limitation on the number of anonymous signatures, that allow applications in many realistic scenarios. We prove security of all proposed schemes and compare their efficiencies with previous schemes.