Data Integrity Auditing (DIA) enables users to remotely verify whether their data saved in third-party clouds has been maliciously tampered with or compromised. As an extension of DIA in certificateless cryptography, certificateless DIA (CL-DIA) integrates the merits of conventional public-key cryptography (no key escrow) and identity-based cryptography (no certificates). However, CL-DIA schemes depend on a reliable third-party auditor (TPA) to perform integrity audits, inevitably suffering from performance bottleneck and single-point failure problems. Moreover, almost all current CL-DIA schemes were designed with computationally expensive bilinear pairings. Cryptanalysis demonstrates that the existing unique pairing-free CL-DIA scheme fails to achieve the unforgeable security of auditing proofs. In this work, we put forward a lightweight blockchain-assisted CL-DIA scheme. The scheme achieves DIA through the blockchain instead of a single TPA, thereby overcoming the problems caused by the TPA-based centralized auditing model. Then, by avoiding time-consuming pairing operations and employing edge servers in generating verifiable tags for the uploaded data of users, its performance surpasses previous pairing-based CL-DIA schemes, particularly in terms of computation efficiency. Furthermore, we provide formal proofs in the random oracle model demonstrating that our scheme achieves unforgeability of verifiable tags and auditing proofs, ensures data privacy secrity, and is resistant to collusion attacks between the EN and the CSP. Finally, experimental results show that when auditing 25 file blocks, our scheme only costs 0.29s, which reduces the total time cost of integrity auditing phase by 48.2%-85.5% compared to current pairing-based CL-DIA schemes.

Searchable public key encryption (SPKE) is a beneficial supplement to traditional public key encryption, which offers a viable method to address the retrieval issue over enciphered data. As a development of SPKE, searchable certificateless encryption enjoys good features of no burdensome certificate management and no key escrow. However, existing searchable certificateless encryption schemes suffer some limitations. Some only support single-keyword search, which often yields inaccurate results. Others enable conjunctive keyword search, which is difficult to cope with data lacking unified keyword fields. In the work, we present a user-friendly certificateless authenticated encryption with field-free multi-keyword search scheme. The proposed scheme eliminates time-consuming operations like bilinear pairing and hash-to-point calculations for data owners and data users. It also enables data users to make multi-keyword searches flexibly on resource-limited mobile devices without concern for keyword orders or positions. As far as we know, it is the first certificateless encryption scheme that supports field-free multi-keyword search. We demonstrate that it has the keyword guessing attack security by formal proofs and show its superior performance by comparisons and experiments. Compared to the state-of-the-art scheme with field-free multi-keyword search, our scheme reduces computation cost for creating a search token and communication cost for sending the search token by about 60% and 56%, respectively.

Vehicular ad hoc networks (VANETs) serve as the foundation of intelligent transportation systems, aiming to improve communication efficiency and safety among vehicles. With the expanding applications, security and privacy have become apparent, and the large-scale message transmission imposes substantial computation and communication overheads. The technology of aggregate signature can realize message authentication and reduce both the bandwidth and computation costs significantly. In IEEE 802.11p-based VANETs, most existing aggregate signature schemes require roadside units (RSUs) to verify single signatures before calculating aggregate signatures, which is very inefficient. Furthermore, even with a valid aggregated signature, the validity of individual signatures cannot be assured. In this paper, we propose an efficient certificateless aggregate signature scheme, where RSUs do not need to validate single signatures but compute aggregate signature directly. The successful verification of the aggregated signature implies the validity of each individual signature. Additionally, to further protect data security and user privacy, this scheme employs designated verifiers for both individual and aggregate signatures. Both formal and informal security analysis are given, and performance evaluation shows our scheme exhibits lower computation and communication costs, along with more comprehensive security attributes in VANETs.

The Internet of Things (IoT) is making the world around us smarter and more convenient. However, its extensive application has rendered security problems, such as the privacy of sensitive data, increasingly serious. Encryption provides an effective and important means of protecting data privacy in the IoT. Because of resource limitations, to achieve high efficiency IoT devices require an encryption scheme that ensures that the encryption phase does not incur a heavy data transmission overhead. By virtue of its many advantages, the use of public-key encryption in current applications is widespread. Identity-based public-key encryption (IBE) removes the obstacle raised by the sophisticated certificate management required by other schemes, and its efficiency renders it more suitable for application in the IoT. However, a problem that needs to be solved in IBE is the revocation of a user whose private key may have been exposed. In this article, we present an efficient and practical IBE scheme having a revocation functionality to preserve data privacy in IoT applications. Elements in the system, such as sensors and actuators, can exchange encrypted data directly or via a cloud server. If a private key is compromised, the private key generator can revoke its user. The security of our proposed scheme can be proved based on SM9 encryption and the bilinear Diffie–Hellman problem.

It is inevitable and evident that outsourcing complicated intensive tasks to public cloud vendors would be the primary option for resource-constrained clients in order to save cost. Unfortunately, the public cloud vendors are usually untrusted. They may inadvertently leak the data or misuse the user’s data, compromise user’s privacy or intentionally corrupt computational results to make the system unreliable. It is therefore important how to stop this happening whilst embracing the computational power of public cloud vendors. Non-negative matrix factorization (NMF) is a significant method for conducting data dimension reduction, which has been widely used in large-scale data processing. Nevertheless, due to its non-polynomial hardness, NMF cannot be conducted efficiently using local computation resources, especially when dealing with big data. Motivated by this issue, we address this by presenting a novel outsourced scheme for NMF (O-NMF), which aims to lessen clients’ computing burden and tackle secure problems faced by outsourcing NMF. Particularly, based on two non-collusion servers, O-NMF exploits Paillier homomorphism to preserve data privacy. Additionally, O-NMF allows a verification mechanism to assist clients in verifying returned results with high probability. Security analysis and experimental evaluation demonstrates that the validity and practicality of O-NMF is also provided in this work.

Abstract With the flourishing development of the Internet of Things (IoT), the electronic health system (EHS) as a leading technology has attracted widespread attention. However, the unsatisfactory network transmission throughput hinders practical applications of EHS to some extent. Network coding can solve this problem, but it also incurs another drawback called pollution attack. Pollution attack can be prevented by using homomorphic network coding signature schemes to check whether a corrupted packet is injected. However, existing schemes require high computational cost for signature verification which will reduce the transmission efficiency. A lightweight certificateless linearly homomorphic network coding signature scheme is proposed. This scheme requires a quite low computational cost when both signing and verifying a data packet. In addition, it is proved that the scheme is secure, and it was implemented by using the Java Pairing‐Based Cryptography Library (JPBC) on a personal computer (PC). The simulation results illustrate that our scheme is efficient.

Certificateless public key cryptosystem (CLPKC) improves the identity based public key cryptosystem to be key‐escrow free. Many research works on CLPKC have been presented so far. However, the revocation problem in CLPKC still lacks effective solutions. The current revocation approaches suffer from either low efficiency or security weakness. In this study, we propose the first ‘scalable revocable’ certificateless encryption (RCLE) scheme against ‘decryption key exposure’. The scheme is provably secure in the standard model. Moreover, we give a second interesting RCLE scheme whose decryption key is very short.

Certificateless encryption (CLE) effectively solves the inherent key escrow problem in identity-based encryption while retaining its keeping certificate-free property. Although a number of CLE schemes have been available in the literature, little attention has been paid to the problem of user revocation in the certificateless setting. In this work, we study CLE systems with user revocation capabilities. At first, we establish reasonable security models for revocable CLE (RCLE) schemes. Then we put forward the first efficient and CCA2-secure RCLE scheme in the standard model. A rigorous security proof of our RCLE scheme is presented based on the decisional truncated q-ABDHE assumption and decisional bilinear Diffie–Hellman (DBDH) assumption.

Certificateless public key cryptography (CL-PKC) is an important type of public key cryptography, which effectively solves the inherent key escrow problem in identity-based public key cryptography. As the adversarial models in CL-PKC are relatively complex, designing efficient and secure certificateless encryption schemes in the standard model has been an interesting and challenging research topic. In this paper, we give cryptanalysis to an existing certificateless encryption scheme in the standard model. We show its insecurity by demonstrating two kinds of attacks. Then, we modify the original scheme to obtain a secure one. A rigorous security proof of the modified scheme is presented in the standard model based on the decisional bilinear Diffie-Hellman (DBDH) assumption and decisional truncated q -ABDHE assumption.