Specialized anonymous credentials and zero-knowledge proofs

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In today's highly connected world, privacy is of increasing importance. Unfortunately, today's electronic economy is quite unfriendly to privacy. When we use credit cards, debit cards, e-passports, or many other modern-day conveniences, data about our actions are logged and disseminated to diverse parties around the world and we have little, if any, control over it. Anonymous credential systems attempt to solve this problem by allowing users to authenticate and prove statements about themselves in a privacy-preserving manner. This is possible due to a cryptographic technique known as zero-knowledge proofs, which allow one party to prove statements to another party without revealing any additional information beyond the validity of the proof. This is a very powerful concept; for example, anonymous credentials can be used to build many useful systems ranging from secure and private electronic cash systems to medical records that reveal no more information about a patient to a health care provider than is strictly needed for that patient's diagnosis and treatment. The research literature contains several general-purpose anonymous credential systems. When coupled with general-purpose zero-knowledge proof systems, these schemes are extremely versatile and make many useful applications theoretically possible. Unfortunately, the wide range of proofs that are possible with these credentials comes at the cost of high computational and communication complexity. As a result, many existing approaches are too costly for use on, e.g., embedded and mobile devices, thereby rendering many potential real-world applications impractical. However, by focusing on special-purpose anonymous credentials, it is often possible to design extremely efficient solutions to particular problems. This work will focus on enlarging the set of problems that are currently practical to solve with anonymous credential systems.