Generalized Collusion and Hop-Skipping Resistant Autonomous Path Proxy Re-Encryption for Blockchain

Blockchain has become a superior carrier for data storage due to its decentralization and immutability. How to realize privacy-preserving data sharing and controlled transfer of blockchain data access rights has become a challenging issue. Autonomous path proxy re-encryption allows the delegator to designate a series of delegatees to obtain decryption privileges according to a predefined sequence in a multi-hop manner. However, it faces the hop-skipping issue, where a malicious proxy can directly re-encrypt the ciphertext to the delegatees several hops afterwards, by skipping one or more delegatees in between, destroying the decryption privileges of the skipped delegatees. Furthermore, the intrinsic nature of proxy re-encryption makes it vulnerable to collusion attack, wherein the proxy and a delegatee might collude to construct a decryption device which can decrypt all the delegator’s ciphertexts, posing a serious threat to the delegator’s privacy. To address these challenging issues, we propose a generalized collusion and hop-skipping resistant autonomous path proxy re-encryption for blockchain (CHRAP-PRE). First, we decentralize the proxy’s privileges of re-encrypting ciphertexts to resist collusion attack. Second, we carefully design the decryption token mechanism so that only the person who gets the correct token can do the decryption, which is authorized by all previous persons in the path, thus controlling the decryption privileges to solve the hop-skipping problem. Finally, we formally prove that our proposed CHRAP-PRE achieves IND-HRA security under the Decisional Bilinear Diffie-Hellman (DBDH) assumption, resisting both collusion and hop-skipping attacks. Our comprehensive performance evaluation demonstrates that our scheme offers enhanced security while reducing communication overhead compared to the state-of-the-art.