Comments on biometric-based non-transferable credentials and their application in blockchain-based identity management

Abstract

In IT-ecosystems, access to unauthorized parties is prevented with credential-based access control techniques (locks, RFID cards, biometrics, etc.). Some of these methods are ineffective against malicious users who lend their credentials to other users. To obtain non-transferability, Adams proposed a combination of biometrics encapsulated in Pedersen commitment with Brands digital credential. However, Adams’ work does not consider the Zero Knowledge Proof-of Knowledge (ZKPoK) system for Double Discrete Logarithm Representation of the credential. Besides, biometrics is used directly, without employing any biometric cryptosystem to guarantee biometric privacy, thus Adams’ work cannot be GDPR-compliant. In this paper, we construct the missing ZKPoK protocol for Adam’s work and show its inefficiency. To overcome this limitation, we present a new biometric-based non-transferable credential scheme that maintains the efficiency of the underlying Brands credential. Secondly, we show the insecurity of the first biometric-based anonymous credential scheme designed by Blanton et al.. In this context, we present a brute-force attack against Blanton’s biometric key generation algorithm implemented for fuzzy vault. Next, we integrate an Oblivious PRF (OPRF) protocol to solve the open problem in Blanton’s work and improve its efficiency by replacing the underlying signature scheme with PS-signatures. Finally, we evaluate application scenarios for non-transferable digital/anonymous credentials in the context of Blockchain-based Identity Management (BBIM). We show that our modified constructions preserve biometric privacy and efficiency, and can easily be integrated into current BBIM systems built upon efficient Brands and PS-credentials.