Improved AB-CPREs with HRA Security

Attribute-based conditional proxy re-encryption (AB-CPRE) schemes offer flexible controls over delegations of decryption rights, and offer an efficient solution for enforcing access control on outsourced encrypted datum. Recently, Liang et al. proposed the first lattice-based AB-CPREs with selective attribute security against chosen-plaintext attacks (CPA) in ESORICS 2021. In this paper, we first show how to construct a CPA secure AB-CPRE scheme which is suitable for circuits in NC1 with polynomially bounded parameters. By contrast, schemes proposed by Liang et al. are only suitable for circuits in NC0 with similar parameters. We then show how to convert our CPA secure AB-CPREs to be secure against honest re-encryption attacks (HRA) under a more reasonable definition. We could show that the CPA security and the HRA security of our schemes are based on standard LWE assumptions for suitable parameters in the standard model.