SyRA: Sybil-Resilient Anonymous Signatures with Applications to Decentralized Identity

We study Sybil-Resilient Anonymous (SyRA) signatures, a cryptographic primitive that enables credentialed users to generate, on demand, unlinkable pseudonyms tied to any given context, and issue signatures on behalf of these pseudonyms. Concretely, SyRA allows a distributed issuer to turn any legacy identity or personhood identifier, possibly of low entropy, into a unique associated cryptographic key of high pseudoentropy, for use in generating signatures for any given context. Sybil-resilient anonymous signatures achieve three main objectives: 1) Sybil resilience: every user is entitled to at most one digital identity, 2) anonymity: no information about the user's real identity is leaked, and 3) non-interactive context switching: users can create on their own at most one credential for any given context in a manner that is unlinkable across contexts.