Privacy-preserving similarity retrieval for ciphertext images has broad applications in Internet of Things (IoT) areas, including smart healthcare, face recognition, and social networking. However, most existing privacy-preserving schemes suffer from inefficient retrieval and limited security guarantees due to the use of unreasonable encryption methods. In addition, those supporting fine-grained access control often lack scalability or are computationally inefficient. To address these challenges, we propose an efficient similarity retrieval scheme for ciphertext images that ensures both privacy preservation and fine-grained access control. First, we construct an encrypted index tree using clustering to improve retrieval efficiency while preserving high recall. Second, we achieve security against chosen-plaintext attacks (CPA) and result verification by employing symmetric homomorphic encryption and Merkle hash tree. Third, we realize access control for each image, enabling simultaneous access verification and similarity retrieval via a single inner product operation. Our theoretical and experimental analysis shows that the proposed scheme is CPA-secure and achieves up to 100× faster query processing than existing CPA-secure schemes, with the ability to retrieve 2000 ciphertext images within 0.5 seconds for 128-dimensional feature vectors.

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.

Many IoT applications require users to share their devices’ location, and enhanced privacy-protection means sharing location anonymously, unlinkably and without relying on any administrators. But under such protection, it is difficult to trust shared location data, which may be from unregistered devices or from the same one’s multiple logins or from the cloned device ID, even be generated by an attacker without any devices! Such untrusted location sharing cheats system, misleads users, even attacks system. To the best of our knowledge, such problems have not been solved in a decentralized system. To solve them in one scheme, we put forward the first decentralized accumulator for device registration and construct the first practical decentralized anonymous authentication for device login. When logging in, the device provides a special knowledge proof, which integrates zero-knowledge (for privacy) with knowledge-leakage (for identifying abnormal behaviors) designing for blockchain (for decentralization). Therefore, in our system, only registered IoT devices can upload location data and their logins are anonymous and unlinkable, while login exceeding${K}$times in a system period or cloning ID to login concurrently can be identified and tracked without any trusted centers. In addition, we provide the security proofs and the application examples of the proposed scheme. And the efficiency analysis and experimental data show that the performance of our scheme can meet the needs of real-world location sharing on IoT.

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 deepening of research, how to construct a fully homomorphic signcryption scheme based on standard assumptions is a problem that we need to solve. For this question, recently, Jin et al. proposed a leveled fully homomorphic signcryption scheme from standard lattices. However, when verifying, it is supposed to unsigncrypt first as they utilize sign‐then‐encrypt method. This leads to users being unable to verify the authenticity of the data first, which resulting in the waste of resources. This raises another question of how to construct an fully homomorphic signcryption (FHSC) scheme with public verifiability. To solve this problem, we propose a leveled fully homomorphic signcryption scheme that can be publicly verified and show its completeness, IND‐CPA security, and strong unforgeability.

Abstract Provable Data Possession (PDP) is of crucial importance in public cloud storage since it allows users to check the integrity of their outsourced data without downloading it. However, the existing PDP schemes, which are based on classical number-theoretic assumptions, are insecure under quantum attacks. In this paper, we propose the first PDP scheme from standard lattices, using a specific leveled fully homomorphic signature (FHS) scheme. To remove the complex key management of PDP cryptosystem on the public key infrastructure (PKI) setting, we employ a specific leveled identity-based (ID-based) FHS scheme to construct the first ID-based PDP scheme from standard lattices. Our two PDP schemes are secure under the standard small integer solution (SIS) assumption, which is conjectured to withstand quantum attacks. Furthermore, we conduct experimental evaluations to validate the feasibility of the proposed PDP schemes in practice.

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.

The revocable ciphertext-policy attribute-based encryption (R-CP-ABE) is an extension of ciphertext-policy attribute-based encryption (CP-ABE), which can realize user direct revocation and maintain a short revocation list. However, the revoked users can still decrypt the previously authorized encrypted data with their old key. The R-CP-ABE scheme should provide a mechanism to protect the encrypted data confidentiality by disqualifying the revoked users from accessing the previously encrypted data. Motivated by practical needs, we propose a new user R-CP-ABE scheme that simultaneously supports user direct revocation, short revocation list, and ciphertext update by incorporating the identity-based and time-based revocable technique. The scheme provides a strongly selective security proof under the modified decisional q -parallel bilinear Diffie–Hellman Exponent problem, where “strongly” means that the adversary can query the secret key of a user whose attribute set satisfies the challenge ciphertext access structure and whose identity is in the revocation list.

Identification schemes support that a prover who holding a secret key to prove itself to any verifier who holding the corresponding public key. In traditional identity-based identification schemes, there is a key generation center to generate all users’ secret keys. This means that the key generation center knows all users’ secret key, which brings the key escrow problem. To resolve this problem, in this work, we define the model of identity-based identification without a trusted party. Then, we propose a multi-authority identity-based identification scheme based on bilinear pairing. Furthermore, we prove the security of the proposed scheme in the random oracle model against impersonation under passive and concurrent attacks. Finally, we give an application of the proposed identity-based identification scheme to blockchain.

Almost all existing well‐known fully homomorphic encryption (FHE) schemes, which are based on either the learning with errors (LWE) or the ring LWE problem, require expensive Gaussian noise sampling. In this study, the authors propose an FHE scheme based on the ring learning with rounding (RLWR) problem. The learning with rounding (LWR) problem was proposed as a deterministic variant of LWE, while the RLWR is a variant of LWR. Sampling an LWR instance does not require Gaussian noise sampling process, and neither does an RLWR instance. Thus, our FHE scheme can be instantiated without the need for Gaussian noise sampling. To implement homomorphic operations, we devise a specific relinearisation method. Furthermore, we also prove that our RLWR‐based FHE scheme is IND‐CPA secure under RLWR assumption.

Very recently, Costache and Smart proposed a fully homomorphic encryption (FHE) scheme based on the Learning with Rounding (LWR) problem, which removes the noise (typically, Gaussian noise) sampling needed in the previous lattices-based FHEs. But their scheme did not work, since the noise of homomorphic multiplication is complicated and large, which leads to failure of decryption. More specifically, they chose LWR instances as a public key and the private key therein as a secret key and then used the tensor product to implement homomorphic multiplication, which resulted in a tangly modulus problem. Recall that there are two moduli in the LWR instances, and then the moduli will tangle together due to the tensor product. Inspired by their work, we built the first workable LWR-based FHE scheme eliminating the tangly modulus problem by cleverly adopting the celebrated approximate eigenvector method proposed by Gentry et al. at Crypto 2013. Roughly speaking, we use a specific matrix multiplication to perform the homomorphic multiplication, hence no tangly modulus problem. Furthermore, we also extend the LWR-based FHE scheme to the multikey setting using the tricks used to construct LWE-based multikey FHE by Mukherjee and Wichs at Eurocrypt 2016. Our LWR-based multikey FHE construction provides an alternative to the existing multikey FHEs and can also be applied to multiparty computation with higher efficiency.