User-Friendly and Expressive Forward-Secure Attribute-Based Signature With Server-Aided Signature and Outsourced Verification

Attribute-based signature (ABS) is an attractive variation of digital signature that enables signers to sign messages with fine-grained signature predicates. In ABS, a signer is able to perform signing operations without revealing personal attributes, and verifiers can only confirm that the signature was created by someone with attributes satisfying a specific signature predicate. However, traditional ABS suffers from key exposure, and the compromise of a signer’s signature key results in invalidating all signatures from him/her. To address this problem, forward-secure ABS (FS-ABS) was introduced. Nevertheless, existing FS-ABS schemes have the shortcomings of low policy expressiveness and high computation costs, and thus are not suitable to be employed on mobile devices with limited resources. In this paper, we propose a user-friendly and expressive FS-ABS (UEFS-ABS) scheme that is proven secure in the standard model. The proposed scheme not only supports expressive signature predicates based on the linear secret sharing scheme, but also provides server-aided signature and outsourced verification functions, significantly reducing the workload of user terminals at both signature generation and verification stages. The experiments indicate that compared with the up-to-date FS-ABS scheme, our scheme reduces the computation costs for signature generation (on signers’ devices) and verification (on verifiers’ devices) by about 85% and 68%, respectively. This makes our scheme more suitable for user terminals in mobile computing scenarios.