IB-VPRE: adaptively secure identity-based proxy re-encryption scheme from LWE with re-encryption verifiability

Abstract

Identity-based proxy re-encryption (IB-PRE) can convert the ciphertext encrypted under Alice’s identity to Bob’s ciphertext of the same message by a semi-trusted proxy with the proper transformation key. The main purpose of our work is to enhance the security of IB-PRE. For outside attacks, all existing IB-PRE constructions from lattices have only achieved a limited or weak security model called IND-sID-CPA security. Therefore, by embedding re-encryption key generation and re-encryption algorithms appropriately in Agrawal et al.’s identity-based encryption scheme from lattices, we construct an IND-ID-CPA secure IB-PRE scheme over decisional learning with errors (LWE) under the standard model. For inside attacks, we propose a new primitive IB-VPRE by extending the basic IB-PRE scheme with a new functionality called re-encryption verifiability, meaning that a re-encrypted ciphertext receiver or a third party can verify whether the received ciphertext is correctly transformed from an original ciphertext or not, and thus can detect illegal activities of the proxy. We realize re-encryption verifiability using the homomorphic signature technique as a black box, making the resulting scheme non-interactive and quantum-immune after instanced by a lattice-based homomorphic signature scheme.