Ciphertext-Policy Attribute-Based Encryption (CP-ABE) schemes with user revocation allow for dynamic updates to users' access rights. However, existing schemes often encounter issues such as low re-encryption efficiency, inflexible access control, and susceptibility to collusion attacks. To address these challenges, we propose UR-CP-ABE, an efficient user revocation scheme built upon a double encryption method. Specifically, UR-CP-ABE stores both valid and revoked users' identity information in a binary tree. This design enables flexible user authority revocation by modifying only the binary tree's relevant secret sub-items. Moreover, the scheme limits the scope of revocation-induced binary tree updates to a single sub-item. This key optimization resolves the critical issue where re-encryption overhead scales linearly with the number of attributes of revoked users. In addition, we eliminate the possibility of attackers constructing secret sub-keys, preventing the collusion attacks. UR-CP-ABE also supports bidirectional revocation, allowing for the revocation and restoration of user rights, which is not available in other related schemes. Our theoretical analysis and experiments demonstrate that UR-CP-ABE has better performance than other schemes, especially in the re-encryption stages. Moreover, UR-CP-ABE has been proved to be secure based on the decisionalq-parallel BDHEhardness assumption in the standard model.

While 5G can facilitate high-speed Internet access and make over-the-horizon control a reality for unmanned aerial vehicles (UAVs; also known as drones), there are also potential security and privacy considerations, for example, authentication among drones. Centralized authentication approaches not only suffer from a single point of failure but they are also incapable of cross-domain authentication. This complicates the cooperation of drones from different domains. To address these limitations, a blockchain-based cross-domain authentication scheme for intelligent 5G-enabled Internet of drones is proposed in this article. Our approach employs multiple signatures based on threshold sharing to build an identity federation for collaborative domains. This allows us to support domain joining and exiting. Reliable communication between cross-domain devices is achieved by utilizing smart contract for authentication. The session keys are negotiated to secure subsequent communication between two parties. Our security and performance evaluations show that the proposed scheme is resistant to common attacks targeting Internet of Things (IoT) devices (including drones), as well as demonstrating its effectiveness and efficiency.