ABSTRACT Title of dissertation: Enhancing Privacy in Cryptographic Protocols

For the past three decades, a wide variety of cryptographic protocols have been proposed to solve secure communication problems even in the presence of adver-saries. The range of this work varies from developing basic security primitives pro-viding confidentiality and authenticity to solving more complex, application-specific problems. However, when these protocols are deployed in practice, a significant challenge is to ensure not just security but also privacy throughout these protocols’ lifetime. As computer-based devices are more widely used and the Internet is more globally accessible, new types of applications and new types of privacy threats are being introduced. In addition, user privacy (or equivalently, key privacy) is more likely to be jeopardized in large-scale distributed applications because the absence of a central authority complicates control over these applications. In this dissertation, we consider three relevant cryptographic protocols facing user privacy threats when deployed in practice. First, we consider matchmaking protocols among strangers to enhance their privacy by introducing the “durability” and “perfect forward privacy ” properties. Second, we illustrate the fragility of for