Using biometric key commitments to prevent unauthorized lending of cryptographic credentials

We present a technique that uses privacy enhancing technologies and biometrics to prevent the unauthorized lending of credentials. Current credential schemes suffer the weakness that issued credentials can be transferred between users. Our technique ensures the biometric identity of the individual executing the Issue and Show protocols of an existing credential system in a manner analogous to the enrollment and verification steps in traditional biometric systems. During Issue we create Pedersen commitments on biometrically derived keys obtained from fuzzy extractors. This issue-time commitment is sealed into the issued credential. During Show a verification-time commitment is generated. Correspondence of keys is verified using a zero-knowledge proof of knowledge. The proposed approach preserves the security of the underlying credential system, protects the privacy of the biometric, and generalizes to multiple biometric modalities. We illustrate the usage of our technique by showing how it can be incorporated into digital credentials and anonymous credentials.