Using Malleable Signatures to Allow Multi-Show Capability in Digital Credentials

In this paper we propose the use of a malleable signature technique to transform Brands’ digital credentials from single-show capability to multi-show capability. Our specific proposed instantiation uses RSA digital signatures so that Alice can efficiently transform an original credential and its corresponding CA signature to a randomized / blinded version of the credential and signature that can be shown to a verifier without risk of traceability (by the CA or across multiple verifiers). We describe our modified issuing and showing protocols and discuss the security properties of our proposed scheme.