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.

Secure off-chain payment plays an important role in blockchain ecosystems, requiring atomicity guarantees where either all payment channels update their balances or none do. While the Lightning Network achieves this through multi-hop Hash Time-Lock Contracts (HTLCs), a critical flaw persists. Specifically, contract conditions (e.g., hash preimages) are transmitted in plaintext across payment paths. Consequently, malicious intermediate nodes can launch interception attacks by claiming funds from predecessors without releasing the corresponding coins to successors. To mitigate this risk, we propose a secure off-chain payment protocol. Firstly, a new cryptographic primitive, namely ciphertext unlinkable autonomous path proxy re-encryption scheme (CUAP-PRE), is proposed. Unlike traditional multi-hop proxy re-encryption, it prevents malicious nodes by enabling the delegator to designate all delegatees he trusts. In addition, ciphertext unlinkability resists homology inference attacks and delegation path tracing to ensure anonymity. Building on CUAP-PRE, a secure off-chain payment protocol (SOCP) in blockchain is designed with an enhanced multi-hop Hash Time-Lock Contract of the Payment-Channel Network (PCN). The receiver at the end of one path of payment channel can control the decryption rights of payment condition in multi-hop delegation manner with reversed order, to unlock the corresponding bitcoins on hold. We then present formal security proofs to demonstrate that the proposed CUAP-PRE and SOCP are postcompromise secure under the Decisional Bilinear Diffie-Hellman (DBDH) assumption in the random oracle model. Comprehensive evaluations also demonstrate the effectiveness and practicability of our proposal.