Biblio

UnlimitID is a method for enhancing the privacy of commodity OAuth and applications such as OpenID Connect, using anonymous attribute-based credentials based on algebraic Message Authentication Codes (aMACs). OAuth is one of the most widely used protocols on the Web, but it exposes each of the requests of a user for data by each relying party (RP) to the identity provider (IdP). Our approach allows for the creation of multiple persistent and unlinkable pseudo-identities and requires no change in the deployed code of relying parties, only in identity providers and the client.

We propose the first verifier-local revocation scheme for privacy-enhancing attribute-based credentials (PABCs) that is practically usable in large-scale applications, such as national eID cards, public transportation and physical access control systems. By using our revocation scheme together with existing PABCs, it is possible to prove attribute ownership in constant time and verify the proof and the revocation status in the time logarithmic in the number of revoked users, independently of the number of all valid users in the system. Proofs can be efficiently generated using only offline constrained devices, such as existing smart-cards. These features are achieved by using a new construction called \$n\$-times unlinkable proofs. We show the full cryptographic description of the scheme, prove its security, discuss parameters influencing scalability and provide details on implementation aspects. As a side result of independent interest, we design a more efficient proof of knowledge of weak Boneh-Boyen signatures, that does not require any pairing computation on the prover side.