MobCred: A New Mobile-Cloud Integration Anonymous Credential Framework With Universal Access Policy

Anonymous credentials are a fundamental cryptographic primitive for achieving privacy-preserving authentication and fine-grained access control. The proliferation of the mobile internet usage has introduced two key requirements for the design of anonymous credentials: (1) enabling lightweight deployment on resource-constrained mobile devices such as smartphones, and (2) supporting expressive and complex access policies required by diverse service providers. However, satisfying both requirements is challenging due to the inherent computational limitations of mobile devices and the substantial resource demands of advanced access policies. To fill this gap, we propose MobCred, a new mobile-cloud integration anonymous credential framework with universal access policy. In MobCred, the credential presentation protocol is partitioned into two components: the mobile user efficiently generates identity and credential proofs, while the cloud servers compute zkSNARK proofs to enforce universal access policies. With the help of the updateable public keys [ASIACRYPT19], the structure-preserving signatures with equivalence classes [JOC19], the Poseidon hash function [USENIXSec21], and the Groth16 protocol [EUROCRYPT16], we present both a generic construction and a concrete construction of MobCred and formally prove its security properties, including unforgeability, unlinkability, and dependability. Rigorous experimental evaluations on smartphones, laptops, and workstations confirm the practical efficiency of our framework.