To ensure the legitimacy of communicators while ad dressing the privacy concerns of vehicles in vehicular ad-hoc networks (VANETs), conditional privacy-preserving authentication (CPPA) schemes have been proposed. Given that existing schemes suffer from single point of failure due to centralized authorities, several distributed CPPA schemes have been proposed. However, these schemes all ignore the tight cementation between system secret keys and the authority, which could be a serious threat to system security, that the compromised authority may leak the system secret key. To address these issues, we propose a security enhanced decentralized conditional privacy-preserving authentication (DCPPA) scheme. DCPPA first introduces a decentralized system master key generation (DSMKG) mechanism without a centralized secret sharer, ensuring that the system secret key remains hidden from any single authority. Based on DSMKG, DCPPA then implements a lightweight verifiable pseudonym self-generation strategy without the system master secret key escrow problem, thus providing flexible pseudonym updating and reliable de-anonymization. Moreover, we implement DCPPA over a hyperelliptic curve cryptosystem (HECC) to balance the system performance. Considering the additional communication processes due to the decentralized feature, we introduce a symmetric balanced incomplete block design (SBIBD) to enhance the communication efficiency. We demonstrate the excellent security of DCPPA through an in-depth security analysis, while demonstrate that the overhead of DCPPA is at ms level through experiments.

Keyword-based auditing (KA) provides a means for users to verify the integrity of only the outsourced data they are interested in. Existing KA schemes employ relation authentication labels to conduct targeted audits with keywords, which significantly improves the cost-effectiveness. However, such schemes typically support only a single-challenge scenario, which may not always be practical. To overcome this constraint, we introduce a hierarchical challenge mechanism grounded in user attributes. This mechanism leverages inequality and affiliation relationships to comply with a predefined tree structure for access policies. Incorporated during the challenge-response phase of the auditing model, it permits users to initiate cross-challenges. Expanding upon this hierarchical mechanism, we propose an attribute-based hierarchical keyword auditing scheme, abbreviated as$\mathcal{AHKA}$.$\mathcal{AHKA}$combines searchable encryption to conduct cross-targeted audits and benefits from the hash collision mapping of Bloom filters to safeguard against keyword guessing attacks. Moreover, we design a fault localization algorithm based on a variant of the binary search technique. It locates in batch the faulty cloud servers and damaged data blocks after an audit failure. As an integral part of$\mathcal{AHKA}$, the algorithm significantly enhances our scheme's practicability. Security analyses indicate that$\mathcal{AHKA}$can effectively withstand both forgery and replace attacks on audit proofs. The smart contract component ensures that our scheme's processes can be monitored and regulated. Experimental data corroborate that deploying$\mathcal{AHKA}$on the client side and on the blockchain is both efficient and feasible.