Revocable ring signatures protect signer anonymity. A trusted authority can revoke signing rights when necessary. This makes them attractive for blockchains and vehicular networks. Existing lattice-based ring signature schemes are only traceable. They can de-anonymize a malicious signer, yet fail to stop the revoked signer from creating a valid signature. This contradicts the very notion of revocation. We introduce a polynomial-based revocation list. It is enforced with non-interactive zero-knowledge proofs of knowledge. Our protocol implicitly verifies the up-to-date revocation list during signature generation. Consequently, revoked signers cannot authenticate and are effectively excluded. Integrating this mechanism into a lattice setting, we obtain a compact revocable ring signature. The scheme is correct, anonymous, unforgeable, and truly revocable under the random oracle model. No costly key updates are required. Compared with prior trace-and-update schemes, our construction offers a practical post-quantum primitive. It guarantees both privacy and accountable revocation. Overhead analysis shows that we have added very little cost while ensuring true revocation.

Abstract Homomorphic signature is an extremely important public key authentication technique for network coding to defend against pollution attacks. However, there are many problems with previous homomorphic signature schemes which require key escrow, cannot resist malicious key generation center (KGC), and are insecure in the post-quantum era. Therefore, we propose a lattice-based certificateless linearly homomorphic signature scheme. In our scheme, certificateless structure can avoid key escrow and malicious KGC. The lattice structure ensures that our scheme is secure in the post-quantum era. The bimodal Gaussian distribution is used to improve the security and the efficiency. Compared with the previous schemes, our scheme has smaller storage space (no key escrow), can avoid malicious KGC, is more secure in the post-quantum era, and has higher signature efficiency. At the same time, our scheme is more suitable for network coding. Finally, under random oracle model, we proved that our scheme is weakly context hiding and existentially unforgeable against adaptive chosen message attacks against external attackers and the internal KGC.

Quantum Anonymous Private Information Retrieval (QAPIR) allows a user to retrieve an item from a database anonymously thus achieving better user privacy. Recently, Khanet al. proposed the first QAPIR protocol [IEEE Trans. Commun. 70(6), 4026-4037 (2022)] which is the only known QAPIR protocol. However, a symbol coincidence error occurs when the main ingredients are combined to form this QAPIR protocol. Furthermore, it requires perfect (n+1)-partited-dimensional Greenberger-Horne-Zeilinger (GHZ) states to be pre-shared among the nodes whereD≥NandNis the size of the database. However, the difficulties in implementing the preparation of high-dimensional GHZ states and the quantum-computing-based queries under current technologies lead to the impracticability of this QAPIR protocol due to the extremely high dimensionalities of GHZ states and oracle operations when large databases are involved. To address these issues, we first point out the symbol coincidence error in Khanet al.’s QAPIR protocol and then give an improvement on it. Finally, we propose a practical QAPIR protocol based on quantum key distribution. We analyze its performance under certain types of noise. We also prove the security of our QAPIR protocol in an active adversary scenario where active dishonest users and database owner are taken into account. Compared with Khanet al.’s protocol, our protocol is easier to implement under current technologies, and can work over the noisy quantum channel.1It provides a practical way for the design of QAPIR protocols.

Summary For the problems that ring signature needs key escrow, has some security risks, and cannot avoid malicious key generation center (KGC) in the post‐quantum era, we design a certificateless ring signature scheme based on lattice (L‐CRSS). In our scheme, the bimodal Gaussian distribution is used to improve the security and efficiency. Compared with the previous ring signature scheme based on lattice, our design does not need key escrow, does not disclose the signer's identity, can avoid malicious KGC, achieves the constant signature size, and has higher security and efficiency in the post‐quantum era. Finally, under random oracle model (ROM), we prove that our scheme is anonymous against the full‐key exposure, and existentially unforgeable against adaptive chosen message attacks (EUF‐CMA).

To improve the efficiency of relevance feedback in image retrieval, an integrated method of long-term learning and active learning is proposed. In early stage, more positive samples are obtained through long-term learning. The problem of biased training samples is effectively solved through a semi-supervised method that uses not only labeled training samples but also unlabeled ones; therefore an accurate initial SVM classifier is obtained. In later stage, through active learning algorithm that selects the most useful samples in database to solicit the user for labeling, samples required for labeling by users decreased largely and convergence rate increased greatly. Experimental results on 5000 Corel images library have shown that the proposed method can greatly improve both the efficiency and the performance, and it can accelerate the convergence to user's query concept as well.