The convergence of software‐defined networking (SDN) and the Internet of Things (IoT) provides a scalable method for handling the considerable volumes of data produced by IoT devices. However, the lack of appropriate security measures can lead to unauthorized access to sensitive data, potential breaches, and privacy violations, as well as time‐consuming and inefficient data retrieval methods in SDN‐IoT systems that require decrypting the entire dataset. To address these challenges, this article proposes the time‐attribute‐based access control scheme in SDN‐IoT (TAAC). The TAAC scheme combines ciphertext‐policy attribute‐based encryption with a novel time‐attribute‐based access tree to ensure fine‐grained access control on time and attributes, enabling secure ciphertext interaction and information sharing across domains. Furthermore, the TAAC scheme also incorporates searchable encryption, which enhances the efficiency of data retrieval. By implementing searchable encryption techniques, the data receiver can generate trapdoors to search and retrieve specific encrypted data without the need to decrypt the entire dataset. In summary, the TAAC scheme improves storage efficiency and computation, enhances scalability, and provides robust security, offering an efficient and secure solution for ciphertext sharing in SDN‐IoT environments. Experimental results have demonstrated that the TAAC scheme shows excellent performance and outperforms other attribute‐based searchable encryption algorithms.

The proliferation of cloud computing technology has led to a significant number of users opting to store image data on the cloud. To ensure the confidentiality of image data, it is recommended to apply encryption techniques prior to uploading them to cloud servers. However, the traditional encrypted image retrieval schemes prove inadequate for practical application scenarios due to limitations in supporting multi-owner and multi-user settings, inefficient access control, and a lack of dynamic verifiability. To address the challenges presented by practical application scenarios, in this paper, we propose a Dynamic and Controllable Image Retrieval scheme in the Multi-owner multi-user settings (DCIRM). First of all, we realize the usability in multi-owner and multi-user scenarios through re-encryption settings. Then, we realize the verifiability of dynamic data by applying the dynamic authentication constructed by the chameleon hash function. Finally, we realize lightweight access control through the polynomial-based access strategy. The DCIRM scheme has been demonstrated to be privacy-preserving, efficient, and feasible through rigorous security analysis and experimentation with authentic datasets.

With the development of new computing models such as cloud computing, user’s data are at the risk of being leaked. Fully homomorphic encryption (FHE) provides a possible way to fundamentally solve the problem. It enables a third party who does not know anything about the secret key and plaintexts to homomorphically perform any computable functions on the corresponding ciphertexts. In 2009, Gentry proposed the first FHE scheme. After that, its inefficiency has always been a bottleneck of the development of practical schemes and applications. At TCC 2019, Gentry and Halevi proposed the first compressible FHE scheme that enables the ratio of plaintext size to the ciphertext size (i.e., the compression rate) to reach 1−ε for any small ε>0 under the standard learning with errors (LWE) assumption. However, it is only a single-key one, where the homomorphic evaluation can only be performed over ciphertexts encrypted under the same key. Compared with single-key FHE, multikey FHE is more practical. Multikey FHE enables ciphertexts encrypted under different public keys to be homomorphically computed without having to decrypt these ciphertexts using their own private keys. In addition, in a multi-identity FHE scheme, only identity information and public parameters are required when encrypting, which simplifies certificate-based key management in public key infrastructure. In this paper, a new compressible ciphertext expansion technique is proposed. Then, we use this technique to construct a compressible multikey FHE scheme and a compressible multi-identity FHE scheme to overcome the bottleneck of bandwidth inefficiency in the multikey and multi-identity settings. The two schemes proposed in this paper make it possible that the objects of homomorphic operation can be the ciphertexts encrypted under different keys or different identities before compression, thus solving the single-key defect of the work of Gentry and Halevi.