Decentralized Physical Infrastructure Networks (DePINs) utilize token incentives to construct permissionless physical infrastructure, but face challenges in ensuring fair compensation for resource contributors. Focusing on bandwidth provision in decentralized data delivery, existing decentralized incentive mechanisms incur prohibitive on-chain costs or employ oversimplified network topologies. We proposeFairRelay, a protocol enablingfair,cost-efficientpayments incomplex multi-hop data delivery. We design two cryptographic primitives: 1)Accountable Multi-hop Data Delivery (AMDD)guaranteeing either correct data receipt or verifiable proof of misbehavior, reducing fair compensation to fee-for-secret exchange; and 2)Enforceable Accumulative HTLC (Enforceable A-HTLC)enabling atomic settlement across multiple off-chain payments via Payment Channel Networks (PCNs). FairRelay's fairness is formally proven within the Universal Composability (UC) framework. Evaluations demonstrate that FairRelay achieveszeroon-chain costs in optimistic execution. Pessimistic scenarios incur constant-cost disputes (O(1) complexity), achieving 13.5% lower overhead than FDE (CCS'24), the state-of-the-art simplified two-party exchange solution (no relays). FairRelay achieves over$95\%$encoding efficiency in 10-hop transmissions.

UAV-based e-commerce, which employs unmanned aerial vehicles (UAV) to deliver commodities from sellers to buyers, plays a central role in the low-altitude economy. In the interests of both buyers and sellers, UAV-based e-commerce usually relies on afair exchangeprotocol between them. Despite extensive research on fair exchange protocol design, UAV-based e-commerce has two features posing extra challenges to achieving mutual fairness:delivery fraudandpath manipulation. On one hand, the UAVs usually deliver real-world commodities rather than virtual assets (e.g., digital books), making it hard to verify the physical delivery status. Particularly, this verification can be easily done for virtual assets by checking their hash values, but inapplicable to real-world commodities, as they cannot be naturally hashed. On the other hand, since UAV costs may vary in different air areas, the seller may manipulate delivery bills by claiming unnecessarily expensive paths. These challenges are newly emerged in UAV-based e-commerce and have not been considered in traditional protocols. The primary goal of this work is to propose thefirstfair exchange protocol that achieving mutual fairness in UAV-based e-commerce. To verify commodity delivery, we develop atracingmechanism that transforms raw UAV-collected footage into immutable delivery evidence, which can be integrated into existing virtuality-oriented protocols for further verification. As for the path manipulation problem, we introduce anauditingmechanism that enables buyers to verify that the chosen delivery path was generated by a trustworthy algorithm (e.g., a well-trained artificial general intelligence model). By establishing these two mechanisms on cryptographic tools, we theoretically prove the fairness of our proposed protocol. We also implement a prototype and observe that the whole protocol has only minute-magnitude cost across different settings, which validates its practicality.

Privacy-preserving blockchain systems are essential for protecting transaction data, yet they must also provide auditability that enables auditors to recover participant identities and transaction amounts when warranted. Existing designs often compromise the independence of auditing and transactions, introducing extra interactions that undermine usability and scalability. Moreover, many auditable solutions depend on auditors serving as validators or recording nodes, which introduces risks to both data security and system reliability. To overcome these challenges, we propose SilentLedger, a privacy-preserving transaction system with auditing and complete non-interactivity. To support public verification of authorization, we introduce a renewable anonymous certificate scheme with formal semantics and a rigorous security model. SilentLedger further employs traceable transaction mechanisms constructed from established cryptographic primitives, enabling users to transact without interaction while allowing auditors to audit solely from on-chain data. We formally prove security properties including authenticity, anonymity, confidentiality, and soundness, provide a concrete instantiation, and evaluate performance under a standard 2-2 transaction model. Our implementation and benchmarks demonstrate that SilentLedger achieves superior performance compared with state-of-the-art solutions.

Secure Aggregation (SA) is a cornerstone of Federated Learning (FL), ensuring that user updates remain hidden from servers. The advanced Flamingo (S&P’23) has realized multi-round aggregation and improved efficiency. However, it still faces several key challenges: scalability issues with dynamic user participation, a lack of verifiability for server-side aggregation results, and vulnerability to Model Inconsistency Attacks (MIA) caused by a malicious server distributing inconsistent models. To address these issues, we propose $\textit{Janus}$, a generic SA scheme based on dual-server architecture. Janus ensures security against up to $n-2$ colluding clients (where $n$ is the total client count), which prevents privacy breaches for non-colluders. Additionally, Janus is model-independent, ensuring applicability across any FL model without specific adaptations. Furthermore, Janus introduces a new cryptographic primitive, Separable Homomorphic Commitment, which enables clients to efficiently verify the correctness of aggregation. Finally, extensive experiments show that Janus not only significantly enhances security but also reduces per-client communication and computation overhead from logarithmic to constant scale, with a tolerable impact on model performance.

The sharing of electronic medical records (EMRs) significantly enhances disease research and healthcare system efficiency. However, outsourcing EMRs to cloud servers introduces risks such as tampering and malicious propagation by recipients. Existing solutions combining blockchain and universal designated verifier signature proofs (UDVSPs) mitigate these risks but rely on secure channels for key sharing, adding communication and computation costs that hinder deployment. In this article, we introduce the first secure channel-free universal designated verifier signature proofs (SCF-UDVSPs) scheme, leveraging simplified cryptographic techniques like the$\Sigma $-protocol and public key encryption. Integrating SCF-UDVSP with blockchain, we develop an optimized EMR sharing system that effectively prevents these attacks, including tampering and malicious propagation. Security proofs and performance analysis validate the feasibility and effectiveness of our proposed system. Compared to existing UDVSP solutions, our approach reduces computational costs by approximately 59.3% without increasing communication overhead, while also eliminating the need for establishing a secure channel.

As Internet technology develops swiftly, the significance of privacy protection is escalating in the realms of e-commerce, e-government and software security. Due to the combination of the benefits of proxy signatures and blind signatures, the proxy blind signature scheme not only distributes the workload across application networks but also effectively safeguards the confidentiality of sensitive information. Additionally, the identity-based proxy blind signature protocol can avoid the problem of heavy certificate management and is widely used in electronic commerce and other scenarios. However, some identity-based proxy blind signature protocols that rely on the large integer factorization problem and the discrete logarithm problem are unable to withstand from attacks from quantum computers. Furthermore, current lattice-based proxy blind signature protocols offer only heuristic security and require three rounds of information exchange during the signing phase. In this paper, we introduce a new two-round identity-based proxy blind signature scheme based on lattices. This scheme utilizes a zero-knowledge proof protocol on lattices as its core component to develop an interactive two-round signature scheme that is free from security proof vulnerabilities. Additionally, we validate the security of the proposed protocol within the random oracle model and conduct a performance analysis.

Zero Trust networks provide an innovative cybersecurity architecture that effectively incorporates “never trust, always verify" principles to address traditional network security threats. Universal Designated Verifier Signature (UDVS) can protect the clients’ privacy in Zero Trust networks, preventing malicious gateways from leaking clients access information to third parties. However, existing UDVS schemes suffer from computational overhead due to their reliance on bilinear pairing operations. This paper primarily focuses on the general transformation method from Identity-Based Key Encapsulation Mechanism (ID-KEM) to UDVS proposed by Steinfeld et al. We first propose ID-KEM based on the SM2 algorithm and prove that it satisfies the EK and Separable properties required by the transformation. Then, we obtain the first UDVS scheme without bilinear pairing through transformation. In terms of performance analysis, the computational overhead of our scheme is 144.36 milliseconds, which is at least 74.39% lower than the previous UDVS schemes. The communication cost is 96 bytes, which is at least 88.89% lower than other schemes, including the first UDVSP scheme without bilinear pairing. To show the utility of our UDVS scheme, we finally apply it into a Zero Trust-based Software Defined Perimeter (SDP) environment, which reaps privacy-preserving authentication for single packet authorization.

Decentralized payment systems, such as Bitcoin, enable immutable, and transparent payments in a distributed manner. To address the issue of user privacy leakage due to transaction transparency, some efforts have enhanced privacy protection in decentralized payment systems. However, the lack of regulatory functions in these systems allows malicious users to engage in illegal activities. To balance user privacy protection and the regulation of malicious users, some efforts have attempted to introduce decentralized agencies. However, they have not considered the issue of agency corruption. In this article, we propose a new traceable privacy-preserving transaction protocol, which tracks the addresses and transaction amounts of anonymous parties through decentralized institutions. To address the problem of committee corruption, we present a traceable privacy-preserving protocol with evolving threshold authentication based on a distributed random beacon (TPETA-to-DRB), enabling committee member updates. Furthermore, we prove that the protocol is secure under the random oracle model and conduct a comprehensive performance evaluation.

While machine learning as a service (MLaaS) enables users to leverage powerful pre-trained models at low cost, it also poses significant intellectual property risks for model builders. A widely adopted defense mechanism is to embed ownership credentials (e.g., watermarking information) into the model, allowing the verifier to examine them during ownership verification. Despite the effectiveness of such watermark-based schemes, we identify a critical vulnerability, termed the model defamation attack (MDA). If an adversary compromises a verifier and obtains the submitted credential, it can reuse this stolen information by embedding it into a malicious modelEˆ and falsely attribute its ownership to the original model builder, thereby damaging their reputation. This paper presents a generic anti-MDA model certification (GAMC) framework that can be seamlessly integrated with existing watermarking schemes to enhance their robustness. We identify two design goals: (1) credential confidentiality, which prevents sensitive watermark-related information from being leaked during verification; and (2) credential non-reusability, which prevents the reuse of any previously submitted credentials. To this end, we employ a cryptographic accumulator to construct the model certification mechanism and design a customized ΣOR protocol as a complement. We formally prove the security of our anti-MDA framework and conduct extensive experiments across various watermarking schemes and neural network architectures to evaluate its compatibility and effectiveness. The experimental results show that GAMC improves robustness against model defamation attacks by 86.67% with negligible overhead, demonstrating its practicality for real-world deployment

Conditional privacy-preserving authentication (CPPA) has been widely studied to ensure authentication, anonymity, and traceability in vehicle ad hoc networks (VANETs). Among CPPA schemes, certificateless CPPA (CL-CPPA) offers natural advantages for VANETs by avoiding the complex certificate management of PKI-based solutions and the key escrow problem of identity-based systems. However, many existing CL-CPPA schemes overlook secure message communication. When confidentiality is required, they often rely on additional encryption, which adds communication overhead comparable to that of certificate transmission in PKI-based solutions. Anamorphic signatures (proposed at CRYPTO'23) can be adopted to address this issue by embedding sensitive messages within signatures, which eliminates the need for separate encryption. However, existing anamorphic signature schemes are symmetric, requiring extensive key agreements between two entities, which is impractical for the dynamic nature of VANETs. In this paper, we introduce a new cryptographic primitive, asymmetric anamorphic signatures (AAS), which enables secure message sharing in a public-key setting, thus eliminating the need for complex key agreements. We also provide a concrete construction of AAS based on a variant of the Hohenberger-Waters signature scheme. By integrating AAS with CL-CPPA, we proposeSphinx, a scheme that ensures authentication, anonymity, traceability, and confidentiality without the overhead of additional secure transmissions or complex key agreements. Our security proofs and performance evaluations demonstrate the practicality and efficiency ofSphinx, particularly its advantage in reducing communication overhead.

Federated learning (FL) in Vehicular Ad Hoc Networks (VANETs) enables vehicles to collaboratively train a global model for intelligent transportation systems while preserving the privacy of their local data. However, the openness and dynamic nature of VANETs introduce significant security challenges, including identity privacy leakage, model inversion attacks, and compromised model integrity. Existing cryptographic solutions, such as differential privacy and homomorphic encryption, provide partial mitigation but suffer from drawbacks including inefficiency, limited data utility, and vulnerability to data poisoning attacks. To tackle these challenges, this paper introduces FedLG, a generic certificateless (CL) authentication scheme with conditional anonymity. FedLG ensures trustworthy FL by integrating multiple security mechanisms that together guarantee model authenticity, data integrity, and privacy. Specifically, FedLG leverages Type-T signatures as a blackbox to ensure the authenticity and integrity of model parameters shared by anonymous vehicles. Additionally, we introduce a novel public key reconstruction mechanism to enhance the security of traditional CL-based systems, effectively mitigating common public key replacement attacks. FedLG also incorporates batch verification with an adaptive group batch verification algorithm, dynamically adjusting batch sizes to identify invalid signatures while preserving valid data, thereby facilitating faster model convergence. Moreover, FedLG maintains the utility of user-contributed data and can seamlessly integrate it with data poisoning attack prevention mechanisms to enhance security further. Experimental results show that FedLG is model-independent, as its integration does not affect the original model’s performance on its dataset. Moreover, it reduces the computational overhead of signature generation and verification by at least 30.8% and 56.3%, respectively, achieving an overall efficiency improvement of 49.69% compared to state-of-the-art FL authentication protocols for VANETs.

As a promising technology, key-aggregation searchable encryption with constant computation overhead is especially suitable for sensor nodes with limited computation resources in wireless sensor networks. However, in most of the existing key-aggregation searchable encryption schemes, the authorized aggregation key is generated in a deterministic way. As a result, these schemes suffer from “Key Forge Attack” and “Trapdoor Forge Attack” that we proposed and hence fail to support the security property as they claimed (which is an important goal to be achieved in key-aggregation searchable encryption schemes). To fix these flaws, in this paper, we identify the security challenges related to key-aggregation searchable encryption and propose a lightweight key-aggregation authorized searchable encryption scheme based on attribute-based encryption, called KA$^{2}$SE. It enables a data owner to share encrypted data with an authorized query user by issuing only a single authorized aggregation key, and the authorized query user only needs to submit a single trapdoor to the cloud server to perform keyword search. We formulate the security definitions for KA$^{2}$SE and prove its security. Finally, empirical evaluations demonstrate that KA$^{2}$SE is computationally efficient in comparison with existing schemes.

Cryptocurrencies possess a natural advantage in financial applications where response time is not critical, given the well-known high latency and low throughput of blockchain technology. However, a notable gap exists in cryptocurrencies, specifically the absence of applications intentionally introducing delays in committing transactions to facilitate potential revocation operations. Large-Value Payment (LVP), a vital component in financial services, addresses this gap by enabling users to perform such operations. In this context, the payer retains the ability to revoke any number of payments within a pre-agreed timeframe T, while the payee gains the unrevoked transactions after T. In the blockchain landscape, trusted third-party platforms play a role analogous to traditional banking institutions, which can trivially realize LVPs. However, their centralized structure poses challenges such as a single point of failure, privacy concerns, and high transaction fees. Motivated by these limitations, we propose trustless large-value payment protocols with key characteristics: (i) trustlessness, eliminating reliance on any trusted party; (ii) revocability, allowing the payer to revoke payments within the predefined time; and (iii) universality, compatible with all current cryptocurrencies. In this paper, we formally define the semantic and security model of LVP, which paves the way for a new research direction. Building on this foundation, we present a straightforward yet efficient construction of LVP based on Bitcoin scripts. To overcome script-dependency limitations, we introduce a scriptless LVP protocol based on verifiable timed signatures and adaptor signatures. This achieves universality across different cryptocurrencies. We prove the security of our proposals in the Universal Composability framework and further enhance performance for multiple LVPs across diverse cryptocurrencies. Specifically, we design a protocol for secure witness reuse and employ verifiable timed discrete logarithm for revocability. Rigorous security analysis and performance evaluation confirm that both scripted and scriptless LVP protocols meet essential security objectives, providing practical solutions for users requiring transaction revocation without relying on trusted parties.

Abstract Cloud storage has been widely used in remote data management, although correct storage of the outsourced file is still challenging in practice. Proofs of Retrievability (PoRs), a storage-oriented cryptographic tool, support integrity checking and efficient retrieval of the file. However, due to the lack of a fully credible oversight mechanism or a serious dependence on a trusted third party, most PoRs are incapable of achieving essential and straightforward trust between participants (i.e. the client and server). While blockchain shows promise in solving this trust issue, existing blockchain-based storage systems are scenario-constrained as they require private/permissioned or special-construct blockchains. Consequently, none of these systems provide robust and decentralized trustworthiness. We propose a general Blockchain-based Automatic Audit (BAA) scheme for PoR without limitations based on specific blockchain types. Specifically, we present BAA via stitching together a carefully designed or chosen array of sub-components such as storage proofs and Turing-complete smart contracts. We also integrate BAA with specific PoR models to prove its strong generality and availability. To our best knowledge, our proposal is the first blockchain-based approach that enhances traditional PoR models with both automatic audit and fair payment. The final analysis and implemented prototype on Ethereum demonstrate the utility of BAA.

Federated Learning (FL) enables multiple clients to collaboratively train a model without sharing their private data. However, the deployment of FL in real-world applications is vulnerable to various attacks from both malicious servers and clients. While cryptographic methods are effective in resisting server-side attacks, they undermine the capability of client-side defenses that rely on plaintext updates. Several valuable defenses targeting hybrid attacks have been devised to address this challenge, concentrating on specific client-side threats. To improve scalability, we continue this research line to introduce a generic architecture covering more client-side attacks. In this paper, we propose a general architecture to enhance client-side defenses from plaintext to ciphertext domains. This architecture not only supports the server-side defenses, but also accommodates a broader range of client-side defenses, including Norm-based, Krum-based, and Cosine-based strategies. The core of our architecture is generic detection under ciphertext, which tackles the following conflict of integrating server-side and client-side defenses. That is, the former aims to protect parameters from exposure while the latter demands plaintext updates. We prove the security of our architecture through the Universal Composability framework. Additionally, we provide a comprehensive instantiation and extensive evaluations to demonstrate the effectiveness and robustness of our approach. Our experiments show that our architecture can maintain the effectiveness of current client-side defenses when parameters are encrypted, thus effectively resisting hybrid attacks.

Threshold anonymous credentials enable users to acquire credentials in a decentralized manner while upholding their privacy. However, distributed network environments, such as electronic voting systems and federated identity management systems, have pressing needs for enhancing security, reducing reliance on fixed-group issuers, and achieving scalability. These requirements expose the significant constraints of existing threshold anonymous credential systems, which struggle to support dynamic threshold settings. This struggle leads to the necessity of system rewinding whenever an issuer is included or excluded. Moreover, the communication and computation complexities involved in showing credentials exhibit a linear relationship with the number of credentials possessed by each user. In this paper, we present a novel dynamic threshold anonymous credential system, named DTACB, to tackle the aforementioned challenges. DTACB enables the dynamic adjustment of thresholds, allowing issuer adjustments without rewinding the system. DTACB additionally supports batch-showing of credentials and proof of credential quantity values while preserving the user’s credentials collection remains undisclosed. We conduct rigorous security analysis and validate our efficiency claims via implementing and benchmarking. In particular, DTACB effectively reduces the cost of batch-proof verification to 3.78 ms, independent of the user’s proof size.

Vehicular Ad-hoc Networks (VANETs) constitute crucial elements within intelligent transportation systems. However, the rapid development of VANETs has brought forth an increasing number of security concerns. Conditional Privacy-Preserving Certificateless Signature (CPP-CLS) has emerged as a promising solution to ensure data security, preserve vehicle anonymity, and establish unlinkability in VANETs. In contrast to traditional public key infrastructure systems that involve cumbersome certificate management, and identity-based frameworks fraught with key escrow issues, CPP-CLS presents a more apt approach for VANETs. Unfortunately, the researches on CPP-CLS present a strange phenomenon in that a scheme proposed is always pointed out to have various security problems, especially public key replacement attacks. Moreover, there is a scarcity of published researches on the generic construction of CPP-CLS. To tackle these challenges, this paper proposes the first generic construction for CPP-CLS based on Type-T (Three-move type) signature, in which the public key reconstruction technique enables any receiver who owns a part of the sender’s public key and the KGC’s public key to reconstruct the complete sender’s public key, which can alleviate the public key replacement attacks. A formal security analysis proves that our scheme effectively guards against existential forgery under adaptively chosen message attacks in the random oracle model, contingent upon the security of the underlying Type-T signature. Furthermore, We provide two specific instantiations of the generic construction to verify feasibility. Among them, the instantiation based on module learning with errors is effective against quantum attacks. Based on extensive experimental results and theoretical analysis, our implementations surpass the majority of existing similar schemes in either performance or security. This substantiates the feasibility of our generic scheme, making it applicable for constructing CPP-CLS schemes.

Payment Channel Networks (PCNs) are innovative second-layer scaling technologies that aim to improve transaction rates, reduce on-chain storage costs, and enable efficient atomic swaps for blockchain-based cryptocurrencies. Despite offering features like relationship anonymity, scriptless script, and cross-chain fairness, current PCNs encounter challenges in achieving identity anonymity and maintaining the fungibility of cryptocurrency units. PayMo, proposed in ESORICS’22, addresses payment anonymity but is limited to Monero, posing difficulties in extending it to a PCN framework. In response, this paper presents a novel Anonymity-Enhancing Multi-Hop Locks (AEMHL) mechanism for Monero-enabled PCNs. The AEMHL mechanism leverages our generic Linkable Ring Adaptor Signature (LRAS) construction and a minimalist PCN framework called anonymous multi-hop locks. This approach effectively combines privacy protection and simplicity while ensuring Monero’s fungibility without the need for specialized scripting support. Security properties, including atomicity, consistency, and anonymity-enhancement, are demonstrated using a universal composability model. Additionally, two optimized LRAS-based schemes are proposed to accommodate multi-hop locks construction in diverse scenarios. Through rigorous security analysis and performance evaluation, we confirm that AEMHL meets essential security objectives and provides efficient and practical solutions for privacy-conscious users within PCNs.

The Industrial Internet of Things (IIoT) incorporates massive physical devices to collect ambient data. Due to the limited types of equipment in IIoT, most of the data has to be saved on a cloud server before it can be processed and analyzed. The ciphertext generated by traditional encryption techniques is difficult to search in subsequent use. Public-key encryption with keyword search (PEKS) can provide data encryption as well as confidential searching, but traditional PEKS schemes are susceptible to internal keyword guessing attacks (IKGAs) caused by the limited space of commonly used keywords. To address this issue, the cryptographic primitive of public-key authenticated encryption with keyword search (PAEKS) was proposed, while most of the existing schemes are not appropriately applied to IIoT for involving time-consuming bilinear pairing operations. In this article, we first propose a user-friendly PAEKS scheme that totally circumvents bilinear pairing operations during generating keyword ciphertext and trapdoor. Then, we prove its multiciphertext indistinguishability (MCI) and trapdoor privacy based on decisional$q$-ABDHE and computational Diffie–Hellman assumptions in the random oracle model together with conducting the theoretical and experimental comparisons. The results show that the computational overhead of our proposal is significantly reduced comparing with most existing classical PAEKS schemes without causing other communication costs or security loss. Due to its better performance and security, our scheme is better suited for lightweight devices in the IIoT.

Vehicular Ad-hoc Networks (VANETs) are with great potentials to facilitate traffic management and improve driver safety. Blockchain-based conditional privacy-preserving authentication (BCPPA) is proposed to achieve an optimal tradeoff among anonymity, traceability and key/certificate management in VANETs. Existing BCPPA protocols mitigate these security and privacy challenges by adding a significant cost on verification and traceability. As a result, current solutions fail to meet high mobility, low latency, and real-time requirements of VANETs. In this paper, we design three new system building blocks namely key derivation (KeyDer), signatures of knowledge (SoK) and smart contract, following by a more efficient BCPPA protocol (named as EBCPA). To show the advantage of EBCPA, we first demonstrate it can satisfy the necessary requirements (e.g. message authentication, conditional privacy protection, resilience to common attacks, and so forth). Moreover, we implement the EBCPA in the on-line Ethereum test network (Rinkeby), Hyperledger test network and VANETs simulation environment (via VanetMobiSim and NS-2). Finally, we evaluate its communication overhead and computational cost via comparing to existing BCPPA protocols that strive to achieve similar properties. From the implementation and comparison results, our proposal can improve efficiency by reducing the time cost of traceability at least 48.95% and verification at least 42.21%.

The rapid development and wide application of blockchain not only highlight the significance of privacy protection (including anonymity and confidentiality) but also the necessity of auditability. While several ingenious schemes such as MiniLedger and traceable Monero supporting both privacy protection and auditability have been proposed, they either provide incomplete privacy protection (only achieving anonymity within a small set or only providing confidentiality but not anonymity), or involve additional auditing conditions such as reaching threshold transaction volume or requiring permissioned nodes to serve as the manager, or restrict to specific blockchain types such as Monero. To mitigate these issues, this article proposes a generic anonymous, confidential, and auditable transaction system (named ACA), which is compatible with both UTXO-based permissionless and permissioned blockchains. Core technologies of ACA include designed traceable anonymous key generation and publicly verifiable authorization mechanisms from existing cryptographic tools (i.e., public key encryption, partially homomorphic encryption, and accumulator) as well as the meticulous designed signatures of knowledge and smart contract. To demonstrate the entity of our proposal, we first prove its security including authenticity, anonymity, confidentiality and soundness, and then provide an instantiation to evaluate its performance. The final implementation and benchmarks show that our proposal can still gain performance advantage even adding more functionalities.

Ethereum leverages ECDSA as the digital signature scheme to validate transactions. From the provable security standpoint, ECDSA built on an 80-bit security Elliptic Curve group can achieve at most 50-bit concrete security, rather than 80-bit security, due to its reduction loss for$2^{30}$signature queries in security analysis. The state-of-the-art ECDSA scheme comes with no de facto formal security guarantee. Although there have been many signatures with higher concrete security, their structures are quite different from ECDSA and a total replacement of the signature field in Ethereum will incur high deployment cost. In this work, we present EthereumX without compromising the signature structure in Ethereum while achieves better security. The security gain is built on top of a new technique named randomness preprocessing module (RPM), which can securely pre-generate and verify randomness with the help of Ethereum. Calling RPM allows to pre-select randomness, which will be used for the subsequent signature, and to verify the randomness, assuring that it is previously generated. We give an instantiation with formal security guarantee and prove that it can be improved to 80-bit concrete security under the same discrete logarithm assumption as ECDSA. From this instantiated scheme, we implement EthereumX via a deployment into a locally simulated network. Experiment results show that EthereumX costs 5 seconds for a block generation which is equal to Ethereum, and generates/verifies at least$17017/10623$transactions per second that is practical enough in application, even if they are slightly slower than Ethereum which generates/verifies at least$17908/11257$transactions per second. We also mention that RMP can be applied to other DL-based signatures for the security improvement.

Electronic Medical Records (EMRs) sharing enhances healthcare and biomedical discoveries but faces challenges: data provider centralization and limited interoperability. Blockchain can address these issues, but existing systems struggle with malicious EMR propagation due to challenges concerning the authenticity, non-repudiation, and integrity of the digital signatures they employ. Universal Designated Verifier Signature Proof (UDVSP) may be an intuitive solution, but existing UDVSP schemes are inefficient due to time-consuming bilinear pairing operations. In this article, we first adopt the Elliptic Curve Digital Signature Algorithm (ECDSA) to propose a more efficient and blockchain-friendly UDVSP scheme, following by a blockchain-based EMR sharing system (EMRChain). To our best knowledge, our proposed UDVSP scheme is the first bilinear pairing-free solution, and EMRChain is the first blockchain-based EMR sharing system to possess the anti-malicious propagation. Furthermore, we proceed to provide a thorough security analysis and performance evaluation of both our UDVSP scheme and EMRChain. Our UDVSP scheme is provably secure within the security model and offers significant computational cost savings (at least 86.76%) and reduced communication overhead (at least 59.37%) compared to existing UDVSP schemes. These results, along with the EMRChain prototype, effectively showcase the utility and effectiveness of EMRChain, which is built upon our UDVSP scheme.

Image licensing regulates the scope, type, and limitations of using an image through an agreement. However, it is challenging to verify whether an agreement has been fulfilled honestly. Existing techniques, such as watermarking and perceptual hashing, help check image originality and editing operations specified in the agreement, but fail to achieve editor designation. In this paper, we propose a verifiable image licensing system (VILS) which provides an effective solution to verify if a received image is used legally according to its licensing agreement. The core building block of our design is a new kind of cryptographic primitive, called accumulator with a designated entity. The new accumulator helps achieve not only editing restriction, but also editor designation in image authentication. Our VILS has the following two appealing features: (1) Authorization: Only an authorized licensee who edits an image with operations declared in a licensing agreement can produce valid images; (2) Efficiency: The verification of VILS is efficient and independent of the number of operations or image size. Compared with the most relevant schemes from the state-of-the-art, the new design enriches the functionality of image authentication but reduces the verification time by 40%.

Outsourcing computations have been widely used to meet the growing computing demands, although achieving trust in an untrusted (or a zero-trust) environment can be challenging in practice. Fair payment, a candidate solution, can potentially facilitate fair trading among outsourcing computation participants such as users and workers. However, most existing solutions including traditional e-cash-based or blockchain-based, may potentially compromise the worker’s fairness (i.e., does not achieve robust fairness, since trusted third parties are required during the trading process), or involve heavy zero-knowledge proofs (ZKPs, with significant computation costs). To mitigate these limitations, we propose a system model of an optimized blockchain-based fair payment (OBFP) for outsourcing computations. Then, we construct a ZKP-free solution based on blockchain by combining any secure commitment, accumulator, and symmetric encryption schemes, as well as a hash function. To demonstrate the utility of our proposed OBFP system, we provide security analysis, performance evaluation and a comparison with existing popular solutions. Specifically, the cryptographic tools are instantiated as commitment (Perdesen commitment), accumulator (RSA-based accumulator), and symmetric encryption (a concrete scheme with the indistinguishability under chosen-plaintext attack (IND-CPA) security), and a hash function (Keccak-256). The prototype is implemented in COSBench and Remix to analyze cloud scalability and concurrency, as well as gas cost.

While Vehicular Ad-hoc Networks (VANETs) can potentially improve driver safety and traffic mangement efficiency (e.g. through timely sharing of traffic status among vehicles), security and privacy are two ongoing issues that need to be addressed. Hence, security solutions such as conditional privacy-preserving authentication (CPPA) protocols have been proposed. However, CPPA protocols are generally far from being ready for deployment in VANETs, for example due key/certificate management limitations in PKI-based protocols or intractable private key updating in ID-based protocols. Although serveral blockchain-based CPPA (BCPPA) protocols have been proposed to mitigiate these challenges, there still exist some intractabilities such as revoking private key, or frequent interactions, or requiring an idea hardware. Thus, in this paper, we are motivated to propose a novel BCPPA protocol without these existing issues. Specifically, we present a PKI-based solution (using a typical digital signature protocol, such as ECDSA) based on Ethereum (a public blockchain), which is designed to facilitate secure communication in VANETs. In other words, we combine the blockchain technology and a key derivation algorithm to realize an effective certificate management. This reduces the need for participating vehicles to store a large number of private keys. To reduce the verification time cost, our BCPPA suppotrs replacing ECDSA with modified ECDSA for batch verification or directly adopting other PKI-based signatures with batch verification. In addition to introducing the concrete design, we also present the security requirements that our BCPPA protocol can satisfy. We then implement BCPPA in the Ethereum test network (i.e.Rinkeby) and provide simulations using VanetMobiSim and NS-2 to show its feasibility (i.e. milliseconds).

The sensing-as-a-service (SaaS) model has been explored to address the challenge of intractability of managing a large number of sensors faced by future smart cities. However, how to effectively share sensor data without compromising confidentiality, privacy protection, and fair trading without third parties is one of critical issues that must be solved in the SaaS in smart cities. While blockchain shows promise in solving these issues, the existing blockchain-based data sharing (BBDS) systems are difficult to apply to SaaS in smart cities because of many unresolved issues such as requiring a customized blockchain, huge storage, communication and computation costs, and dependence on a third party to achieve fair trading. We propose a BBDS system model with its security requirements before we present a concrete construction by combining -protocol, Paillier encryption scheme, and any secure symmetrical encryption and signature schemes. To demonstrate the utility of our proposed BBDS system, we present a security analysis and compare our system with other solutions. We implement the prototype in Remix to analyze the gas cost, and we conduct experiments to evaluate the communication and computation costs of the BBDS system using symmetric encryption (advanced encryption standard (AES)) and a signature scheme (elliptic curve digital signature algorithm (ECDSA)).

Increasingly, governments around the world, particularly in technologically advanced countries, are exploring or implementing smart homes, or the related smart facilities for the benefits of the society. The capability to remotely access and control Internet of Things (IoT) devices (e.g., capturing of images, audios, and other information) is convenient but risky, as vulnerable devices can be exploited to conduct surveillance or perform other nefarious activities on the users and organizations. This highlights the necessity of designing a secure and efficient remote user authentication solution. Most of the existing solutions for this problem are generally based on a single-server architecture, which has limitations in terms of privacy and anonymity (leading to users' daily activities being predicted), and integrity and confidentiality (resulting in an unreliable behavior auditing). While blockchain-based solutions may mitigate these issues, they still face some critical challenges (e.g., providing regulation of behaviors and privacy protection of access policy). Motivated by these facts, in this article, we construct a novel secure mutual authentication system, which can be applied in smart homes and other applications. Specifically, the proposed approach integrates blockchain, group signature, and message authentication code to provide reliable auditing of users' access history, anonymously authenticate group members, and efficiently authenticate home gateway, respectively. We also prove the security and privacy requirements, including anonymity, traceability, and confidentiality, that the proposed system satisfies, with an implementation and evaluation to demonstrate its practicality.

Blockchain, a distributed ledger technology, can potentially be deployed in a wide range of applications. Among these applications, decentralized payment systems (e.g. Bitcoin) have been one of the most mature blockchain applications with widespread adoption. While the early designs (e.g. Bitcoin) are often the currency of choice by cybercriminals (e.g., in ransomware incidents), they only provide pseudo-anonymity, in the sense that anyone can deanonymize Bitcoin transactions by using information in the blockchain. To strengthen the privacy protection of decentralized payment systems, a number of solutions such as Monero and Zerocash have been proposed. However, completely Decentralized Anonymous Payment (DAP) systems can be criminally exploited, for example in online extortion and money laundering activities. Recognizing the importance of regulation, we present a novel definition of Decentralized Conditional Anonymous Payment (DCAP) and describe the corresponding security requirements. In order to construct a concrete DCAP system, we first design a Condition Anonymous Payment (CAP) scheme (based on our proposed signature of knowledge), whose security can be demonstrated under the defined formal semantic and security models. To demonstrate utility, we compare the performance of our proposal with that of Zerocash under the same parameters and testing environment.