Collusion-Resistant Identity-based Proxy Re-encryption

An identity-based proxy re-encryption scheme allows the semi-trusted proxy to convert ciphertexts encrypted under Alice’s public identity into the ciphertexts encrypted under Bob’s public identity. The proxy cannot learn any information of the underlying message. As in other delegation schemes, identity-based proxy re-encryption scheme should be secure against collusion, especially of the proxy and a delegatee. Unfortunately, no collusion-resistant identity-based proxy re-encryption with CCA-security and non-interactivity has not been proposed yet. In this paper we propose a novel collusion-resistant scheme which enjoys useful properties such as unidirectionality, non-interactivity and nontransferablity. We show that our approach using two secret keys is sufficient to achieve the CCA-security and actually minimizes a security loss from the collusion attack. This result affirmatively resolves the open problem posed by Koo et al..