Privacy-Preserving OpenID Connect
Sven Hammann, Ralf Sasse, David Basin
Abstract
OpenID Connect is the most widely used Internet protocol for delegated authentication today. It provides single sign-on functionality for users who use their account with an identity provider to authenticate to different services, called relying parties. Unfortunately OpenID Connect is not privacy-friendly: the identity provider learns with each use which relying party the user logs in to. This necessitates a high degree of trust in the identity provider, and is especially problematic when the relying parties' identity reveals sensitive information. We present two extensions to OpenID Connect that address this privacy concern. We first present a simple extension that prevents the identity provider from learning to which relying parties its users log in, and we further extend this solution to also prevent colluding relying parties from tracking users. We give formal security proofs for both standard OpenID Connect and our extensions using the Tamarin security protocol verification tool.