Attribute-based Anonymous Credentials with Update Broadcast

Abstract

Attribute-based anonymous credentials (ABC) allow users to prove possession of attributes (e.g., ages and addresses) to verifiers using credentials issued by trusted issuers. When considering updating credentials on attributes, each user has different credentials, and an issuer usually requires the credentials as input to update them. If the issuer could generate a common update token without taking user-specific information like their credential as input and broadcast this token, and each user updates their credential on their own, the issuer can reduce the communication and computation cost when updating. However, existing ABC schemes and their variants do not support this functionality. In this paper, we introduce ABC with update broadcast (ABC-UB), which enables an issuer to update each user's credentials by broadcasting a common update token. Each user can update their credentials using the token on their own. This feature reduces the issuer's communication and computation costs when updating credentials. In addition, the credential size on our ABC-UB scheme is constant, and the update token size is also constant. To construct an ABC-UB scheme, we introduce a new digital signature scheme called unlinkable redactable signature with update broadcast (URS-UB) and construct a concrete URS-UB scheme from pairings. Our URS-UB can generate a common update token without taking existing signatures as input.