Compartmented secret sharing schemes form an important category within secret sharing, characterized by a compartmented access structure where the participant set is divided into parts, and all participants within the same part assume equivalent roles. In this paper, we introduce explicit constructions of ideal linear secret sharing schemes that realize compartmented access structures using partial MDS (PMDS) codes. We first present the construction methodologies for two new families of PMDS codes. Utilizing the specialized structure of these codes, we then offer efficient explicit constructions of ideal linear secret sharing schemes that accommodate compartmented access structures, complete with both upper and lower bounds. Notably, our approach is distinguished by the use of PMDS array codes, unlike existing literature that typically employs scalar codes for such constructions.

The interconnected environment of the Internet of Vehicles (IoV) facilitates the development of various low-carbon and secure location-based services. However, sharing data with semi-trusted service providers poses serious security risks. In particular, it can threaten the confidentiality of past messages after the leakage of the user’s key. In this article, we propose an efficient and forward-secure conditional privacy-preserving scheme for IoV, namely, EFSC. We construct a cryptographic method with forward secrecy in the proposed EFSC scheme, which ensures the confidentiality of past messages even after the user’s secret key has been compromised. This method incorporates key derivation functionality and efficiently addresses the complex certificate management issue with the assistance of smart contracts. Additionally, the designed smart contract facilitates authentication. We analyze and prove that the proposed EFSC scheme satisfies the proposed privacy and security requirements with better security performance. We use Goerli, an Ethernet test network, to deploy customized smart contracts to prove its feasibility. Furthermore, the proposed EFSC scheme exhibits high-index generation and pairing efficiency and realizes less computational and communication overhead. Compared with the existing schemes, its computational overhead in message signing, signature verification, and user revocation can be reduced by up to 95.61%, 36.53%, and 67.01%, respectively. Moreover, the communication overhead for initiating a location service query is only 0.3760 kB. These results show that the proposed EFSC scheme has certain advantages regarding efficiency and security.

Blockchain systems have evolved over decades, addressing the inefficiencies and high costs associated with centralized architectures. Among various consensus mechanisms, committee-based hybrid Byzantine Fault Tolerant (BFT) protocols are a fundamental approach to blockchain consensus. However, designing a hybrid BFT consensus protocol that ensures fairness, responsiveness, and formal security remains challenging. In this paper, we propose GRBFT: a Gaussian reputation-based hybrid BFT blockchain consensus protocol with a formal security framework. Our proposed protocol integrates a multilateral Gaussian reputation evaluation to incentivize trusted nodes' participation in the consensus. We use threshold signatures and verifiable random functions (VRFs) to randomly select committee members and leaders, ensuring fair reconfiguration and unbiased sortition. A formal security framework is utilized to design and analyze the blockchain consensus system. Additionally, we design a speculative GRBFT (S-GRBFT) protocol to circumvent the traditional$\mathcal {O}(n^{2})$leader sortition complexity and reduce the communication to$\mathcal {O}(n)$within a single round. Moreover, we present a secure candidate committee reconfiguration method that efficiently updates members based on their reputation and a Proof-of-Stake (PoS) mechanism. The proposed GRBFT protocol is proven to achieve consistency and liveness under the corruption and liveness parameters.

The private intersection-sum with cardinality (PIS-CA) protocol enables two parties to privately compute the cardinality of the intersection between their datasets and the sum of the values associated with these intersecting elements, while keeping all other information confidential. As a related variant of private set intersection (PSI), private set intersection with cardinality (PSI-CA) protocols compute only the intersection size without considering the associated values. Existing PIS-CA protocols attempt to reduce the amount of communication through batch encryption-based optimization, but their incomplete design and implementation hinder their practical deployment. Moreover, the shuffle proof withO(√n) communication complexity adopted in their protocol incur substantial communication overhead, further limiting their scalability. To address these problems, we propose an optimized two-sided PIS-CA protocol in the malicious model. Our scheme provides a concrete and implementable batch encryption design that achieves practical communication efficiency, together with an enhanced lightweight shuffle proof based on the Curdleproofs framework. The experimental results demonstrate that the proposed protocol significantly reduces the total communication cost, making it suitable for privacy-preserving applications such as ad conversion measurement.

Based on known bounds for relative generalized Hamming weights of linear codes, we provide several new bounds for generalized column distances of convolutional codes, including the Griesmer-type bound for generalized column distances. Then we construct several infinite families of convolutional codes such that the (1, 1)-Griesmer defect of these convolutional codes is small compared with the length of these convolutional codes by using cyclic codes, negacyclic codes and GRS codes. In particular, we obtain some convolutional codes such that the (1, 1)-Griesmer defect of these convolutional codes is zero or one. Next we prove that the 2-generalized column distance sequence$\{d_{2,j}(\mathcal {C})\}_{j=1}^{\infty }$of any convolutional code$\mathcal {C}$is increasing and bounded from above, and the limit of the sequence$\{d_{2,j}(\mathcal {C})\}_{j=1}^{\infty }$is related to the 2-generalized Hamming weight of the convolutional code$\mathcal {C}$. For$i\ge 3$, we prove that thei-generalized column distance sequence$\{d_{i,j}(\mathcal {C})\}_{j=\lceil \frac {i}{k}-1\rceil }^{\infty }$of any convolutional code$\mathcal {C}$is bounded above and below.

Efficient and secure data sharing in the Internet of Vehicles (IoV) is critical for the advancement of intelligent transportation, particularly in the context of emerging 5G/6G networks and driverless technology. This has prompted researchers to explore Blockchain-based Internet of Vehicles (BIoV) solutions to address common issues in intelligent transportation systems (ITS). However, at the edge layer, existing reputation and consensus mechanisms in the BIoV model face challenges such as significant energy consumption, limited scalability, and pronounced centralization. To tackle these issues, we introduceTRCO, a Permissioned Blockchain-basedTrusted andRobustConsensusOptimization orienting ITS.TRCOis a three-layer BIoV architecture applicable to any BIoV scenario, offering robust scalability with the addition of new sub-regions. To improve the quality of data sharing for edge layer, we propose a decentralized reputation evaluation mechanism and integrate PoS and PBFT consensus algorithms to enhance performance by evaluating the communication behavior of edge servers. Security analysis and simulation experiments demonstrate thatTRCOachieves high scalability and reliability, effectively filters Byzantine edge servers, and enhances the decentralization and consensus efficiency of the system.

Committee-based blockchain consensus is a fusion of permissionless consensus and the permissioned Byzantine Fault- Tolerant (BFT) classical protocol. However, three enduring challenges remain: the formal framework for the Proof-of-Stake (PoS)-based hybrid consensus, the dynamic adjustment of committee size and the definition of consensus time-bound. To tackle these challenges, in this paper, we present a Stackelberg game-driven fair committee-based blockchain consensus protocol, dubbed SG-FCB, which combines PoS and reputation-based blockchain hybrid BFT consensus. The SG-FCB protocol lever-ages an unbiased BLS-threshold signature and a random shuffle algorithm to achieve fair leader election and committee reconfiguration seamlessly. Specifically, the variant-BFT is designed to maintain the low communication cost of$\mathcal{O}(n)$, and a Stackelberg game-based incentive mechanism is proposed to jointly maximize the individual profit of the validators and the expected consensus committee responsiveness efficiency of blockchain user. Rigorous security analysis shows that for an adversary with a stakeholding fraction less than 1/3 and sufficient reputation value, we define the time bound for consensus, and the SG-FCB protocol achieves consistency and liveness properties by reasonably setting a corruption parameter and liveness parameter within a formal framework.

With the application of blockchain in Internet of Things (IoT), various IoT scenario-oriented blockchains have been proposed, meaning that multichain future within IoT ecosystem is growing. Cross-chain interoperability thus is essential. Sidechains is one of the crucial technologies for cross-chain interoperability, which allows blockchains to interoperate with each other. However, sidechains encounters practicability challenges impeding adoption, such as poor generality and inefficiency. In this article, we propose practical and secure sidechain construction (PSSC)in the form of parent-child chains, a practical and secure sidechains construction for heterogeneous blockchains orienting IoT scenarios. To achieve practicability, we first utilize succinct noninteractive argument of knowledge (SNARK), which is succinct noninteractive proof (arguments) of knowledge, to reproduce the state transition of blockchains, so that PSSC can get rid of the constraints on consensus mechanisms of blockchains; we then design an impawn-punish mechanism based on smart contract, which transfers the work verifying SNARK proof from mainchain to sidechain, preventing fork threat to mainchain. Due to employing SNARK based on recursive proof composition to generate cross-chain proof, our PSSC is more efficient with succinct cross-chain proof, reducing the overhead of storage of nodes. Besides, we formally prove our PSSC satisfies the three fundamental security properties of sidechains: 1) persistence; 2) liveness; and 3) firewall. Finally, we develop a proof-of-concept implementation of PSSC, and the experimental results show that the proof size of PSSC is about 28.8 kB, which is roughly$2094\times $,$9.36\times $,$6.56\times $,$4.23\times $, and$3.27\times $smaller than BTCRelay proof, PoW sidechains proof, PoS sidechains, zkRelay proof, and fast sidechains, respectively.

The emergence of 5G/6G networks has sparked new potentials for Internet of Things (IoT) scenarios, such as vehicle ad hoc networks (VANETs), inspiring numerous scholars to leverage Blockchain-based Internet of Vehicles (BIoV) solutions to address prevailing issues in VANETs. However, the dynamic and decentralized nature of VANETs presents significant challenges in terms of security and privacy, hindering data providers from engaging in the data-sharing process. Furthermore, the reliability of edge nodes and system architecture in the BIoV paradigm faces several challenges, including limited consensus participation, high resource consumption, poor scalability, and centralization. To mitigate these challenges, we propose RTSP, a robust and trusted service protocol for VANETs, based on a distributed ledger technology. RTSP advocates a novel three-tier BIoV architecture suitable for any permissioned BIoV application scenario. To improve the quality of data sharing, we design a decentralized reputation mechanism. This mechanism mitigates the performance bottleneck induced by consensus transactions by measuring the historical behavior of roadside units (RSUs). Empirical evidence from simulation experiments and security performance analyses substantiates RTSP’s capabilities. It can hinder the number of faulty RSUs from increasing while simultaneously improving data-sharing efficiency, simplifying communication complexity, and enhancing system scalability and consensus stability.

The technology for securely sharing data has grown extensively in recent years. Many users are willing to share their lightweight mobile device data via social networks or the cloud. A novel matchmaking encryption primitive was proposed in CRYPTO’19, whose potential for privacy protection and data sharing security was introduced. However, matchmaking encryption technology faces challenges in flexibly realizing critical functions, such as one-to-many non-interactive scenarios, no key escrow problem, stronger security, lightweight computation and low communication overheads for mobile devices, which impede their widespread application. To achieve the above functions, we present a lightweight certificateless multi-user matchmaking encryption (LC-MUME) for mobile devices, which enhances security flexibly and performance based on standard hard assumptions and low-consumption pairing-free technology, while also avoiding one-by-one encryption for each user. The proposed LC-MUME scheme enjoys minor computation and communication overheads in a one-to-many non-interactive certificateless cryptosystem. We prove that our scheme achieves indistinguishability-based chosen-ciphertext attack (IND-CCA) security, the existential unforgeability under a chosen message attack (EU-CMA) security and anonymity-CCA security under the random oracle model. Our LC-MUME scheme outperforms the state-of-the-art schemes regarding efficiency and flexibility, as demonstrated by the performance comparison and analysis, and therefore is a practical solution for resource-constrained mobile devices.

Vehicular ad hoc networks (VANETs) establish wireless connections among all vehicles, enabling seamless mobile communication. However, existing conditional privacy protection VANETs authentication schemes fail to address the issue of potential key-exposure and do not provide accelerated vehicle authentication. In this paper, we propose a reputation incentive committee-based secure conditional dual authentication scheme for VANETs called RIC-SDA. Our proposed scheme incorporates dual authentication of the consensus committee and vehicle-to-vehicle (V2V) communication. It enables the rapid provision of dynamic vehicle epoch-key from consensus committee authentication for V2V authentication through our designed reputation incentive mechanism. To mitigate the potential key-exposure problem, we introduce a novel concept of secure vehicle epoch communication, which means V2V authentication is valid for only one epoch blockchain unit time. The proposed scheme achieves lightweight computation and incurs minimal communication overheads, with the signature size being just 137 bytes. The RIC-SDA scheme supports fast batch verification. We prove that our proposed scheme is unforgeable security under random oracle and demonstrate its feasibility by implementing it in a test network based on Ethereum Sepolia. The results demonstrate that our RIC-SDA solution outperforms the existing state-of-the-art authentication VANET schemes regarding efficiency and communication costs.

Matchmaking encryption is a method employed to address the security and privacy concerns of cloud-enabled IoT healthcare. Nevertheless, matchmaking encryption technology encounters challenges in effectively implementing critical functionalities, such as resolving a single-key-exposure problem, achieving secure short-epoch communication, and simultaneously enabling lightweight computation and communication overheads for IoT healthcare. These challenges pose obstacles to the widespread adoption of this technology. To tackle these constraints, we first present aReputation incentive committeeConsensus-based forMatchmakingEncryption in IoT healthcare (RCME), which utilizes consensus nodes to eliminate the single-key-exposure problem and enables fast provision of permission proof based on our design reputation incentive mechanism. The proposed RCME scheme adopts low-consumption pairing-free technology to realize lightweight matchmaking encryption in a multi-party, non-interactive certificateless cryptosystem. Rigorous security analysis shows it achieves chosen ciphertext attack security under the random oracle model. To further reduce consensus communication overhead from$\mathcal {O}(n^{2})$to$\mathcal {O}(n)$, we propose an optimized Practical Byzantine Fault Tolerance (PBFT) consensus, and we adopt reputation incentive mechanism and threshold cryptography technology to achieve unbiased leader election. The comprehensive evaluation corroborates that our solutions outperform the existing state-of-the-art schemes regarding security and performance. Therefore, our RCME scheme is a practical solution for resource-constrained IoT healthcare devices.

The Industrial Internet of Things (IIoT) and cloud computing have developed rapidly in recent years. Many enterprises are willing to outsource lightweight devices’ industrial data via the cloud to lower manufacturing costs and enhance production efficiency. The data sharers, however, usually have concerns about the security and privacy of their data stored in cloud outsourcing systems. Traditional certificateless searchable encryption primitives are tough to realize dynamically revocable and high-efficiency decryption. Furthermore, data sharing on untrusted devices may cause a single-key exposure problem. To address these issues, we propose a blockchain-assisted secure data-sharing protocol with a dynamic multiuser keyword search (DMUKS) in IIoT, which utilizes blockchain-assisted techniques to solve a single-key exposure problem and to realize fast certificateless keyword search as well as dynamic user and key management. The proposed DMUKS scheme enjoys minor computation and communication overheads. It maintains a constant ciphertext and trapdoor query size as users increase and supports user addition and revocation. Moreover, it periodically supports key and ciphertext updating and is secure against keyword-guessing attacks under the random oracle model. The performance comparison and analysis demonstrate that it is more efficient and flexible than the existing data sharing with keyword search schemes.

Data management services provided by the public cloud can economize the enterprise’s local storage costs, and meanwhile, realize data sharing among the enterprise. Corporate users, however, usually have concerns about the security and privacy of their data stored in the public cloud. Searchable encryption has been used as a secure method for enterprise users in the public cloud to share data via keyword search for many years. Nevertheless, conventional search and encryption primitives are challenging to realize several critical functions flexibly, such as key update, user revocation, lightweight computation, and low communication overhead for users, which will impede their widespread application. Besides, it may cause single-key-exposure security concerns by using untrusted devices. To address these issues, we present a dynamic consensus committee-based for secure data sharing with authorized multi-receiver searchable encryption (called DCC-SE), which exploits the blockchain dynamic committee to eliminate a single-key-exposure problem and enables fast keyword search without pairing and dynamic user management. The proposed DCC-SE scheme enjoys minor computation and communication overheads. It maintains a constant ciphertext size as the receiver increases. Furthermore, it periodically supports secure key and ciphertext updating and has been proven secure against chosen plaintext attacks and the chosen keyword guessing attacks under the random oracle model. The performance evaluation results show that DCC-SE has more feasibility and higher efficiency than the previous public key with keyword search(PEKS) schemes through theoretical analysis and simulation studies.

Abstract For the purpose of improving the efficiency of the cryptosystems built upon lattice trapdoors, Chen, Genise and Mukherjee at ASIACRYPT 2019 modified the gadget trapdoor (G‐trapdoor) to an approximate trapdoor, which enables one to sample short preimages approximately from a discrete Gaussian distribution. The implementation shows that the sizes of the hash‐and‐sign signature scheme can be reduced to 3.67 kB for an estimation of 81.67‐bit security, and 9.97 kB for an estimation of 168.81‐bit security. In this study, the spherical sampling method is adapted to the non‐spherical setting, without leaking any information about the trapdoor. Due to the fact that the signature size and the concrete security are closely related to the Gaussian parameter of the sampling algorithm, this technique provides a tradeoff between them. Specifically, two modes of parameters were set up for different goals. (a) Mode 1 admits to achieve the ‘win–win’ scenario, that is, gain concrete security and simultaneously reduce the signature size. Our proof‐of‐concept implementation shows that for an estimation of 94.5‐ and 185.88‐bit security, the signature sizes can be reduced to 3.3 and 6.98 kB. (b) Mode 2 aims mainly to further reduce the signature sizes, without a decrease in the security level. The implementation shows that the signature size can be reduced to 2.35 kB for an estimation of 81.67‐bit security, and 5.75 kB for an estimation of 168.82‐bit security.

Summary Many schemes for privacy‐preserving machine learning have been proposed over the past decade. Often, the entities want to keep the privacy of their data while performing machine learning tasks collaboratively, and institutions or end‐users are with limited computing and storage resources. To overcome these issues and to take benefits of cloud computing, it is possible to outsource the execution of a machine learning task to a computing service while retaining confidentiality of the participant's data. Clustering is one of the commonly used tasks in various machine learning and data mining applications. In this paper, we demonstrate that, by using homomorphic encryption, it is possible to outsource the execution of a two‐party k‐means clustering algorithm to a single cloud server while retaining confidentiality of the test data. To the best of our knowledge, ours is the first reasonable scheme to discuss the two‐party k‐means clustering algorithm to a single cloud server.

Multipartite secret sharing is an important research object in the area of secret sharing schemes. Compartmented access structures are an interesting class of multipartite access structures. The constructions of ideal linear schemes realizing compartmented access structures are studied by codes in this paper. We find that compartmented secret sharing is related to a class of codes called locally repairable codes which are being used widely in distributed and cloud storage systems. We study secret sharing schemes for compartmented access structures with upper bounds, compartmented access structures with lowers bounds and compartmented access structures with upper and lower bounds. We establish the relationships between secret sharing schemes for these compartmented access structures and locally repairable codes. Based on the relationships and some locally repairable codes, we obtain ideal linear schemes realizing these compartmented access structures by efficient methods.

Multipartite secret sharing schemes are those having a multipartite access structure, in which the set of participants is divided into several parts and all participants in the same part play an equivalent role. Secret sharing schemes for multipartite access structures have received considerable attention due to the fact that multipartite secret sharing can be seen as a natural and useful generalization of threshold secret sharing. This work deals with efficient and explicit constructions of ideal multipartite secret sharing schemes. Most ideal multipartite secret sharing schemes in the literature can be classified as either hierarchical or compartmented. The main results are the constructions for ideal hierarchical access structures, a family that contains every ideal hierarchical access structure as a particular case such as the disjunctive hierarchical threshold access structure and the conjunctive hierarchical threshold access structure, the constructions for three families of compartmented access structures, and the constructions for two families compartmented access structures with compartments. We present an efficient method to construct ideal linear schemes realizing these access structures by linear algebraic techniques on the basis of the relationship between multipartite secret sharing schemes, polymatroids and matroids.

Double-authentication-preventing signature (DAPS) is a novel signature notion proposed at ESORICS 2014. The double-authentication-preventing property means that any pair of signatures on two different messages with the same subject will result in an immediate collapse of the signature system. A few potential applications of DAPS have been discussed by its inventors, such as providing a kind of self-enforcement to discourage certificate authority (CA) from misbehaving in public key infrastructure and offering CA some cryptographic arguments to resist legal coercion. In this study, we focus on some fundamental issues on DAPS. We propose a new definition, which is slightly weakened but still reasonable and strong enough to capture the DAPS concept. We develop the new notion of invertible chameleon hash functions with key exposure. Then we propose a generic DAPS scheme, which is provably secure if the underlying invertible chameleon hash function with key exposure is secure. We instantiate this general construction to obtain the DAPS schemes respectively based on the well-known assumptions of integer factorization, Rivest-Shamir-Adleman (RSA), and computational Diffie-Hellman (CDH). They are more efficient than previous DAPS schemes. Furthermore, unlike previous constructions, the trusted setup condition is not needed by our DAPS schemes based on RSA and CDH.

A code over a finite alphabet is called locally repairable codes (LRCs) if every symbol in the encoding is a function of a small number of other symbols of the codeword. In this paper, we study LRCs with heterogeneous locality constraints. We introduce (n, k, ri, δi, i ∈ [m]) LRCs which generalize the LRCs with equal (r, δ)-locality, and establish the Singleton-like bound for such codes. Then, we study how to construct optimal LRCs, namely, its minimum distance attains the proposed bound. In precisely, we redefine the notation of LRCs with maximal recoverability (MR-LRCs) based on the proposed LRCs and show that MR-LRCs are optimal LRCs. Finally, we construct a family of MR-LRCs which extend the construction of LRCs with equal locality presented by Rawat et al.

Nowadays, Internet of things (IoT) become more and more popular. At the same time, the requirements of security mechanism for multimedia in IoT received a huge concern. Multimedia data is easily shared by devises, applications and social networks set by IoT. Therefore, it is indispensable to guarantee the privacy and security of shared multimedia data. In this paper, we address the secure multimedia data sharing problem in cloud computing by designing proxy re-encryption (PRE) scheme. Our schemes cope with the issues of data validity, data confidentiality and authentication during encrypted multimedia data sharing. Unlike as usually done in the literature, we present a CCA-secure PRE scheme which removes pairings firstly. Then we design a refined CCA-secure PRE scheme called publicly verifiable PRE without parings. It is demonstrated that our schemes meet not only the security and high efficiency requirements of multimedia data sharing, but also the public verifiability. The validity of ciphertext, both the original and re-encrypted ciphertext, can be publicly verified which brings additional efficiency due to offloading the validity check of ciphertexts from the power-limited clients to any semi-honest public cloud.

Summary With the dramatic growth of smart phones and social network services, location‐based service has become increasingly popular in our daily life, which also brings great privacy leakage about user's location information. Thus, privacy‐preserving location sharing is still a significant problem. In this paper, two models of our scheme are verifiable, supporting location query on homomorphic encrypted ciphertext with searching index and trapdoor. The characteristics of our scheme are that it (1) allows users to share their current location without leaking any location information to the untrusted server; (2) protects users from the cheating of untrusted server's malicious behavior by verifying query result; (3) supports a novel personalized query according to users' classifications of social network friends; (4) the user does not have to be online to make permissions for accessing his shared location, and (5) model 2 does not rely on any trusted third party server to perform any computation. The security analysis shows that it ensures secure location sharing in social scenarios.

Summary With the advent of cloud computing, more and more consumers prefer to use the cloud services with the pay‐as‐you‐consume mode. The cloud storage brings about great convenience to users, who store data in cloud and access to it using the smart devices anytime and anywhere. Consumers' information should be encrypted to guarantee the data privacy. Flexible searching on ciphertext is a critical challenge to be solved for effective data utilization. In this paper, we propose a novel semantic keyword searchable proxy re‐encryption scheme for secure cloud storage. A highlight of this work is that the scheme is quantum attack resistant, while most of the available searchable encryption schemes are not. It supports not only exact keyword search but also synonym keyword search. Moreover, the data owner is capable to delegate his search right to another user using the proxy re‐encryption mechanism. In the generation process of re‐encryption key, the delegator and delegatee do not need to be interactive with each other. The scheme is also collusion resistant. Under the learning with errors hardness problem, this scheme is proved secure in standard model.

Computations over biometric data performed on untrusted cloud environment raises important concerns about the privacy of biometrics data. Face recognition has been widely applied in a variety of enterprise, civilian and law enforcement. Many schemes for privacy-preserving face recognition (PPFR) have been investigated over the past decade. In order to protect individuals' privacy, face recognition is performed over encrypted face images. However, these results increase the computation cost of the client and the face database owners with limited computing and storage resources. To overcome this kind of issue and to take benefits of cloud computing, outsourcing such tasks to the cloud environment has recently gained special attention. Currently, no secure techniques for outsourcing face biometric recognition are readily available to make client and the face database owners free from encryption and decryption operations. We consider the scenario where a client and a database owner of face images securely outsource their data to the cloud and ask the cloud to perform the face recognition task on their combined data in a privacy-preserving manner. We term such a process as privacy-preserving and outsourced face recognition (PPOFR). We propose a novel and efficient scheme to the PPOFR problem with outsourced computation for the first time under a federated cloud environment based on the Eigenfaces algorithm, which efficiently protects data confidentiality of the participating entities under the standard semi-honest model. To the best of our knowledge, ours is the first work to discuss and propose a comprehensive solution to the PPOFR problem that incurs negligible cost on the participating entities. We theoretically estimate both the computation and communication costs of the proposed protocol.

In a proxy re-encryption (PRE) scheme, a semi-trusted proxy can convert a ciphertext under Alice's public key into another ciphertext that Bob can decrypt without accessing the underlying plaintext. This property adds flexibility in various applications, such as cloud data sharing. In this paper, we study CCA-secure, single-hop unidirectional PRE schemes without pairings. We gain high efficiency and public verifiability which enables anyone to publicly verify the validity of the original ciphertexts and re-encrypted ciphertexts. With public verifiability, we can offload the integrity check of the wellformedness of ciphertexts from power-restrained clients to any honest-but-curious untrusted public cloud for improved efficiency.

Cloud computing is an emerging computing paradigm in which IT resources and capacities are provided as services over the Internet. It also brings forth new challenges for security when clients want to securely outsource the computation of operations to the untrusted cloud servers. In cloud computing, it is difficult to implement most of cryptographic protocols among clients for this reason that all clients are possibly weaker than computationally powerful players. Hence, clients have to appeal to cloud servers for assistance. However, cloud servers are untrusted so that cryptographic protocols cannot be realized securely. In this paper, we design a secure key agreement scheme for two weaker clients who delegate cloud server to compute modular exponentiation. In our scheme, two clients can get same key for symmetric cryptosystem even that cloud server is untrusted.

A linear code is optimal if the length of code is the shortest among all linear codes which realize the given access structure. It is a difficult problem how to obtain the optimal linear code for any access structure. In this paper, we firstly construct the optimal linear codes for realizing any given non-threshold multi-access structures over finite field Fq. Then, based on our optimal linear code, we construct the optimal linear multi-secret sharing scheme for any non-threshold multi-access structure.

Abstract An on‐line/off‐line threshold signature (𝒪𝒯𝒮) scheme is a distributed cryptosystem in which a group of players jointly generate a signature for a message and use the on‐line/off‐line technique to improve the efficiency of signing. An 𝒪𝒯𝒮 scheme can be applied to large‐scaled distributed data storage systems and can highly improve the efficiency of writing files. There are two approaches to construct an ordinary threshold signature scheme: the direct approach and the simulation approach. Owing to its simplicity, people tend to use the simulation approach, in which the security of a threshold signature scheme is reduced to the security of its underlying (and simpler) signature scheme. The security proof in this approach is based on a theorem that guarantees the validity of the security reduction—we call this theorem the simulation theorem. However, the simulation theorem (and thus the simulation approach) for an ordinary threshold signature scheme cannot be applied to the on‐line/off‐line cases, because partial signature exposure problems might occur in these cases. This paper presents a simulation theorem for the on‐line/off‐line cases, where the security of an 𝒪𝒯𝒮 scheme is reduced to the security of a so‐called divisible on‐line/off‐line signature scheme. This provides a theoretical basis for constructing an 𝒪𝒯𝒮 scheme through the simulation approach. Furthermore, through this approach, we present a concrete 𝒪𝒯𝒮 scheme, which is efficient and its security proof is simple. Copyright © 2009 John Wiley & Sons, Ltd.