SaTC: CORE: Small: Mercurial Signatures and Applications to Privacy-Preserving Authentication

Brown University, Providence RI

Investigators

Abstract

Anonymous credentials allow individuals to prove that they have a set of credentials, issued by some trusted issuer, or a set of issuers, without revealing any other information. Thus, for example, using anonymous credentials, an access provider can make sure that only authorized individuals get to participate in transactions and gain access to various resources, without invading the individuals' privacy. In spite of decades of research, the existence of several implementations and some examples of adoption, practitioners have yet to adopt this technology en masse. One reason that practitioners are having a tough time wrapping their minds around anonymous credentials is that the underlying concepts are complex and have yet to enter the popular lexicon. Another issue is that traditional anonymous credentials do not in fact protect users' privacy as much as we want them to. Efficiency, bandwidth and other practical considerations play a role too. This work addresses these gaps by studying mercurial signatures. Conceptually, mercurial signatures are easier to explain to software engineers and decision makers than traditional anonymous credentials, because unlike the latter they do not require familiarity with cryptographic commitments and zero-knowledge proof systems. Instead, they build off intuition that, by now, many practitioners have from standard digital signatures when it comes to unforgeability, and probabilistic encryption when it comes to unlinkability. They immediately lend themselves to privacy-preserving certification chains and delegatable anonymous credentials. And their efficient realization translates to efficient privacy-preserving authentication with strong composition guarantees. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.