Zero-knowledge Succinct Non-interactive Argument of Knowledge (zkSNARK) is a powerful cryptographic primitive that enables a prover to convince a verifier that something is true without leaking the private witness. Current zkSNARKs face significant computational costs in generating proofs, which restricts their use in areas like private payments, confidential smart contracts, and anonymous credentials. Private delegation offers a practical solution by outsourcing the heavy computation to powerful external workers without leaking any private information. In this work, we propose HyperSiniel, an efficient private delegation framework for general zkSNARKs that achieves a new feature called guaranteed output delivery (GOD). HyperSiniel is designed to be compatible with any universal zkSNARKs constructed from a polynomial interactive oracle proof (PIOP) and a polynomial commitment scheme (PCS). It enables a computationally limited delegator to outsource proof generation to several workers in a fully non-interactive and privacy-preserving manner. Compared to the most state-of-the-art frameworks (e.g., Siniel [NDSS'25]), HyperSiniel ensures that the delegator always receives a correct proof, regardless of malicious worker behavior. We implement HyperSiniel and compare the performance with Siniel across varying bandwidths and circuit sizes. Under low-bandwidth conditions (10MBps), HyperSiniel incurs only an additional 25% overhead compared with Siniel, while the total running time of HyperSiniel is almost identical to Siniel under high-bandwidth settings (1000MBps). These results show that the strong robustness guarantee of GOD in HyperSiniel comes almost for free, making it a practical and secure solution for real-world zkSNARK delegation.

Cloud computing, as a persuasive paradigm, offers on-demand data services. However, it faces various security threats during data sharing due to trust issues. To mitigate this problem, many cloud-based data-sharing systems employ cryptographic tools to guarantee the confidentiality of sensitive data. Nevertheless, fine-grained data sharing still suffers from many challenges, especially in complex cloud environments. In this paper, we introduce two cloud-based data-sharing systems with fine-grained access control. The first solution supports dynamic user groups, while the second solution further offers outsourced decryption, enabling compatibility with resource-constrained devices. To formalize our solution theoretically, we introduce the concept of ElGamal -type cryptosystem (ETC) and server-aided ETC with key encapsulation mechanism to generalize public-key encryption with specific features implicitly specified by ElGamal encryption. Through the application of ETC, we present generic constructions for revocable attribute-based encryption (RABE) and server-aided RABE (SR-ABE) with formal definitions and security analyses. These schemes serve as the fundamental mechanisms behind our proposed solutions. By applying the state-of-the-art attribute-based encryption scheme proposed in CCS'22, we introduce instantiations of RABE and SR-ABE with various desirable properties, including large universe, attribute multi-use, key exposure resistance, fast decryption, and more. Extensive experiments substantiate the superior performance of our proposed instantiations over previous solutions.

Aiming to provide people with great convenience and comfort, smart home systems have been deployed in thousands of homes. In this paper, we focus on handling the security and privacy issues in such a promising system by customizing a new cryptographic primitive to provide the following security guarantees: 1) fine-grained, privacy-preserving authorization for smart home users and integrity protection of communication contents; 2) flexible self-sovereign permission delegation; 3) forward security of previous messages. To our knowledge, no previous system has been designed to consider these three security and privacy requirements simultaneously. To tackle these challenges, we put forward the first-ever efficient cryptographic primitive called the Forward-secure Hierarchical Delegable Signature (FS-HDS) scheme for smart homes. Specifically, we first propose a new primitive, efficient Hierarchical Delegable Signature (HDS) scheme, which is capable of supporting partial delegation capability while realizing privacy-preserving authorization and integrity guarantee. Then, we present an FS-HDS for smart homes with the efficient HDS as the underlying building block, which not only inherits all the desirable features of HDS but also ensures that the past content integrity is not affected even if the current secret key is compromised. We provide comprehensively strict security proofs to prove the security of our proposed solutions. Its performance is also validated via experimental simulations to showcase its practicability and effectiveness.

As an advanced one-to-many public key encryption system, attribute-based encryption (ABE) is widely believed to be a promising technology for achieving flexible and fine-grained access control of encrypted data on untrusted storage servers (e.g., public cloud servers). However, user revocation in ABE is a critical but challenging problem, and designing efficient revocable ABE has been an active research topic in the past decade. Almost all the existing revocable ABE schemes incorporate a timestamp in the encryption algorithm such that revoked users cannot decrypt ciphertexts generated in future time intervals. To prevent revoked users from decrypting past ciphertexts, the storage server needs to perform a process called ciphertext delegation (Sahai et al., CRYPTO’12) that periodically updates the timestamp for all ciphertexts. As the number of ciphertexts could be huge in a storage system, ciphertext delegation could pose a huge computation overhead to the server.Motivated by the popularity of commodity Trusted Execution Environment (TEE) technologies, this paper initiates the study on hardware-based revocable ABE (HR-ABE) to eliminate the (unscalable) ciphertext delegation and prevent collusion attacks between an untrusted storage server and revoked users. We formalize this new notion and present an efficient HR-ABE construction that also supports outsourced decryption for resource-constrained data users. Furthermore, HR-ABE is also designed to address the potential secret leakage problem suffered by TEE (e.g., due to side-channel attacks) so that the leakage of secrets possessed by TEE does not lead to leakage of user data. We prove HR-ABE’s security formally and benchmark its performance experimentally.

Time series data analytics technology significantly benefits modern scientific research, especially in fields such as medical health, financial investment, and transportation. Unfortunately, privacy issues hinder people from handing over the data to a third party for various analytical tasks; because the data may reveal much more individual sensitive information, e.g., disease information from medical data, investment tendency from financial data, or the daily trajectory from transportation data. To break down this barrier, secure computation approaches have shown their importance in processing sensitive data, and have attracted much attention from the industry and research communities. However, when considering the case of secure time-series data analytics (e.g., DTW similarity), we are still far from achieving high efficiency due to high round complexity in communication or expensive computational complexity. We observe that DTW involves a lot of comparison operations and existing approaches in dealing with the comparison require higher communication costs. To this end, this paper studies secure DTW-based analytics with practical efficiency over time series data. Specifically, we propose the framework of secure time series data analytics (STDA) and formulate the problem of top-$k$query for outsourced time series data. Based on threshold Paillier encryption, we present a top-$k$query protocol utilizing the DTW distance as a metric and its security analysis, optimizations, and performance evaluation. The experimental results demonstrate that in a wide-area network with a 10 ms latency, our top-$k$approach outperforms the state-of-the-art by 3x times, while DTW calculation outperforms by 9x times. Correspondingly, the optimized$\mathcal {F}_{\text {DTW}}$achieves 17x times better, and optimized top-$k$achieves 4-10x times better.

Federated learning (FL) allows multiple parties, each holding a dataset, to jointly train a model without leaking any information about their own datasets. In this paper, we focus on vertical FL (VFL). In VFL, each party holds a dataset with the same sample space and different feature spaces. All parties should first agree on the training dataset in the ID alignment phase. However, existing works may leak some information about the training dataset and cause privacy leakage. To address this issue, this paper proposes OpenVFL, a vertical federated learning framework with stronger privacy-preserving. We first propose NCLPSI, a new variant of labeled PSI, in which both parties can invoke this protocol to get the encrypted training dataset without leaking any additional information. After that, both parties train the model over the encrypted training dataset. We also formally analyze the security of OpenVFL. In addition, the experimental results show that OpenVFL achieves the best trade-offs between accuracy, performance, and privacy among the most state-of-the-art works.

Secure outsourced computation is critical for cloud computing to safeguard data confidentiality and ensure data usability. Recently, secure outsourced computation schemes following a twin-server architecture based on partially homomorphic cryptosystems have received increasing attention. The Secure Outsourced Computation on Integers (SOCI) toolkit is the state-of-the-art among these schemes which can perform secure computation on integers without requiring the costly bootstrapping operation as in fully homomorphic encryption; however, SOCI suffers from relatively large computation and communication overhead. In this paper, we propose SOCI+ which significantly improves the performance of SOCI. Specifically, SOCI+ employs a novel (2, 2)-threshold Paillier cryptosystem with fast encryption and decryption as its cryptographic primitive, and supports a suite of efficient secure arithmetic computation on integers protocols, including a secure multiplication protocol (SMUL), a secure comparison protocol (SCMP), a secure sign bit-acquisition protocol (SSBA), and a secure division protocol (SDIV), all based on the (2, 2)-threshold Paillier cryptosystem with fast encryption and decryption. In addition, SOCI+ incorporates an offline and online computation mechanism to further optimize its performance. We perform rigorous theoretical analysis to prove the correctness and security of SOCI+. Compared with SOCI, our experimental evaluation shows that SOCI+ is up to 5.3 times more efficient in online runtime and 40% less in communication overheads.

Blockchain as an open and immutable ledger is being posited as the next frontier in healthcare that will help solve the industry's interoperability challenges. However, immutability in processing personal data is no longer legal since the General Data Protection Regulation (GDPR) requires the “right to be forgotten” as a critical data subject right. To observe such data regulation, it is desirable to build a healthcare blockchain with data redaction in a controlled way. Moreover, electronic health records (EHRs) usually are sensitive and the conventional blockchain lacks systematic and formal security analysis of data confidentiality, especially in the multi-user setting. Furthermore, EHRs are typically helpful in medical research for predicting epidemic diseases and valuable in insurance agencies making business plans. Hence, in healthcare blockchain systems, data confidentiality and flexible key distribution have become the most challenging issues that should be urgently resolved. In this paper, we propose a privacy-preserving and redactable healthcare blockchain system (PRHBS). Our solution offers fine-grained block-level data reduction and secure data sharing with flexible key distribution mechanisms. We give the formal definition and security models of PRHBS, and propose a generic construction based on trapdoor-based chameleon-hash function, attribute-based encryption, and puncturable encryption. We present formal security analysis and give an instantiation based on our proposed generic construction. The comprehensive comparison and experimental simulation demonstrate that our implementation exhibits comparable performance, while surpassing the most relevant solutions in terms of functionality.

Following the success of cloud computing, it has been shown its importance to realize various access control models in the cloud storage setting. Chinese Wall is a traditional access control model in business for solving the conflict of interest (CoI) problem, and it would be very interesting to achieve conflict-resistant in cloud storage system. However, the access control model does not ensure the privacy of users, and it may reveal the user's interest, investment tendency, etc. Therefore, it raises a big challenge to implement the Chinese Wall without compromising the user's privacy. In this paper, we focus on the Chinese Wall model and apply it to the cloud storage while protecting the access patterns of users. Specifically, we first formulate the tree-based Chinese Wall access control and then propose the Chinese Wall Protocol (called C-Wall). We prove that our C-Wall not only realizes the conflict-resistant but also protects the user's privacy with universally composable security. Besides, we also apply C-Wall to privacy-preserving cloud storage and propose the C2-Wall, which not only maintains C-Wall's features, but also ensures the sensitive files from being touched by "honest-but-curious" cloud servers. Furthermore, we evaluate our C2-Wall by theoretical analysis and experimental validation. Experimental results show its effectiveness and efficiency for practical deployment.

Mobile crowdsensing (MCS) systems typically struggle to address the challenge of data aggregation, incentive design, and privacy protection, simultaneously. However, existing solutions usually focus on one or, at most, two of these issues. To this end, this paper presents CROWDFA, a novel paradigm for privacy-preserving MCS through federated analytics (FA), which aims to achieve a well-rounded solution encompassing data aggregation, incentive design, and privacy protection. Specifically, inspired by FA, CRWODFA initiates an MCS computing paradigm that enables data aggregation and incentive design. Participants can perform aggregation operations on their local data, facilitated by CROWDFA, which supports various common data aggregation operations and bidding incentives. To address privacy concerns, CROWDFA relies solely on an efficient cryptographic primitive known as additive secret sharing to simultaneously achieve privacy-preserving data aggregation and privacy-preserving incentive. To instantiate CROWDFA, this paper presents a privacy-preserving data aggregation scheme (PRADA) based on CROWDFA, capable of supporting a range of data aggregation operations. Additionally, a CROWDFA-based privacy-preserving incentive mechanism (PRAED) is designed to ensure truthful and fair incentives for each participant, while maximizing their individual rewards. Theoretical analysis and experimental evaluations demonstrate that CROWDFA protects participants’ data and bid privacy while effectively aggregating sensing data. Notably, CROWDFA outperforms state-of-the-art approaches by achieving up to 22 times faster computation time.

Person re-identification (Person Re-ID) is widely regarded as a promising technique to identify a target person through surveillance cameras in the wild. Nevertheless, person Re-ID leads to severe personal image privacy concerns as personal images are stipulated by laws and guidelines as private data. To address these concerns, this article explores the first solution for building a privacy-preserving person Re-ID system. Specifically, this article formulizes privacy-preserving person Re-ID as similarity metrics of encrypted feature vectors because the underlying operation of person Re-ID is to compute the similarity of feature vectors that are extracted from person images by a machine learning model. However, feature vectors are generally denoted by floating-point numbers. To this end, this article exploits a series of new encoding mechanisms and secure batch computing protocols to encrypt floating-point feature vectors and achieve the underlying operation of person Re-ID. Rigorous theoretical analyses demonstrate that this work achieves person Re-ID without compromising any personal image privacy. Furthermore, the proposed secure batch protocols significantly enhance the performance of privacy-preserving person Re-ID while outputting the same precision as the previous method.

With the advent of cloud computing, it has become more and more popular to outsource various services to the cloud for releasing the burden of local data storage and maintenance. However, it may cause serious privacy problems because the cloud may be untrusted. In this article, we study the privacy-preserving reverse nearest neighbor (PPRNN) query over encrypted spatial data. First, we introduce the concept of reference-locked order-preserving encryption (RL-OPE) with its construction and security proof, which reveals less information than traditional order-preserving encryption (OPE). Then, we present a novel PPRNN scheme in static setting based on structured encryption (SE) and the proposed RL-OPE, called sPPRNN. After that, we design a generic method that extends a PPRNN scheme in static setting to the counterpart in dynamic setting, called dPPRNN. Furthermore, we present a thorough privacy analysis of our proposal. Finally, we demonstrate its efficiency and effectiveness for practical deployment through extensive experiments.

Smart home is a good exemplification of the Internet of Things (IoT). Many researchers study how to make smart home systems (SHS) smarter. However, the security of SHS is also worth studying as user's information is collected from the devices and security-sensitive data are communicated through an open network. Therefore, how to guarantee the security of the data transmission in SHS is an important problem. In this paper, we propose a new secure data transmission scheme with access control to protect the data transmission in SHS. In our scheme, data transmission is secured by a new cryptographic primitive called access control encryption (ACE). Different from other existing solutions in SHS, our scheme controls not only which messages smart devices can receive, but also which messages they can send. Our experimental results demonstrate the effectiveness and efficiency of our proposed mechanism.

Perceptual image encryption provides an efficient and effective way to preserve the confidentiality of visual information, and the measurement of content leakage is of fundamental importance for perceptually encrypted images. Numerous visual security indexes (VSIs) have been proposed to evaluate visual content leakage. Due to the lack of perceptually encrypted image databases, image quality assessment (IQA) databases are widely adopted to evaluate the performance of existing VSIs. However, there are huge differences between VSIs and IQAs. The misuse of databases may lead to an inaccurate evaluation. In this paper, we propose a perceptually encrypted image database (PEID) which contains 1080 encrypted images from 20 plain images with 10 well-known perceptual encryption techniques. Both visual quality and content leakage scores of the encrypted images are obtained through a comprehensive subjective evaluation. We also propose a systemic methodology to accurately evaluate the monotonicity, fitness, and accuracy of VSIs. We conduct extensive experiments on the proposed PEID to evaluate the performance of existing state-of-the-art VSIs. We have made the database publicly available for download and hope that the proposed PEID can facilitate the research of visual security evaluation and beyond.

Perforations in flexible endoscopy are life-threatening. Defect closure or suturing in flexible endoscopy has long been a critical challenge due to the confined space of the access routes and surgical sites, high dexterity and force demands of suturing tasks, as well as critical size and strength requirements of wound closure. This paper introduces a novel robotic suturing system for flexible endoscopic surgery. This system features a flexible, through-the-scope, five-degree-of-freedom robotic suturing instrument. This instrument allows the surgeon to endoscopically manipulate a needle via a master console to create running stitches and knots in flexible endoscopy, which is not possible with existing devices. Successful ex-vivo trials were conducted inside porcine colons to show how surgical stitches and knots can be endoscopically created and secured in a completely new way. This new technology will change the way how surgeons close defects or perforations in flexible endoscopic surgery.

Ensemble learning plays an important role in big data analysis. A great limitation is that multiple parties cannot share their knowledge extracted from ensemble learning model with privacy guarantee, therefore it is a great demand to develop privacy-preserving collaborative ensemble learning. This paper proposes a privacy-preserving collaborative ensemble learning framework under differential privacy. In the framework, multiple parties can independently build their local ensemble models with personalized privacy budgets, and collaboratively share their knowledge to obtain a stronger classifier with the help of central agent in a privacy-preserving way. Under this framework, this paper presents the differentially private versions of two widely-used ensemble learning algorithms: collaborative random forests under differential privacy (CRFsDP) and collaborative adaptive boosting under differential privacy (CAdaBoostDP). Theoretical analysis and extensive experimental results show that our proposed framework achieves a good balance between privacy and utility in an efficient way.

In practice, the greatest threat against the security of a digital signature scheme is the exposure of signing key, since the forward security of past signatures and the backward security of future signatures could be compromised. There are some attempts in the literature, addressing forward-secure signature for preventing forgeries of signatures in the past time; however, few studies addressed the backward-security of signatures, which prevents forgeries in the future time. In this paper, we introduce the concept of key-evolving signature with bilateral security, i.e., both forward security and backward security. We first define the bilateral security formally for preventing the adversaries from forging a valid signature of the past and the future time periods in the case of key exposure. We then provide a novel construction based on hub-and-spoke updating structure and the random oracle model, and show that the construction achieves bilateral security and unbounded number of time periods. Finally, we compare our scheme with the existing work by rigorous analysis and experimental evaluation, and demonstrate that our construction is more secure and efficient for practical applications.

With the development in recent decades of various efficient image encryption algorithms, such as selective encryption, a great demand has arisen for methods of evaluating the visual security of encrypted images. Existing solutions usually adopt well-known metrics of visual quality assessment to measure the quality of encrypted images, but they often exhibit undesired behavior on perceptually encrypted images of low quality. In this paper, we propose a novel visual security index (VSI) based on the human visual system. The proposed VSI evaluates two aspects of the content similarity between plain and encrypted images: the edge similarity extracted via multi-threshold edge detection and the texture similarity measured by means of the co-occurrence matrix. These two components are further integrated to obtain the proposed VSI through adaptive similarity weighting. Extensive experiments were performed on two publicly available image databases. Our experimental results demonstrate that compared with many existing state-of-the-art visual security metrics, the proposed VSI exhibits a better performance and stability on low-quality images.