Blockchain Papers

Ning Ni, Yongxin Zhu

No abstract is available for this record.

Mohit Bhasi Thazhath, Jan Michalak, Thang Hoang

The audit log is a crucial component to monitor fine-grained operations over sensitive data (e.g., personal, health) for security inspection and assurance. Since such data operations can be highly sensitive, it is vital to ensure that the audit log achieves not only validity and immutability, but also confidentiality against active threats to standard data regulations (e.g., HIPAA) compliance. Despite its critical needs, state-of-the-art privacy-preserving audit log schemes (e.g., Ghostor (NSDI '20), Calypso (VLDB '19)) do not fully obtain a high level of privacy, integrity, and immutability simultaneously, in which certain information (e.g., user identities) is still leaked in the log. In this paper, we propose Harpocrates, a new privacy-preserving and immutable audit log scheme. Harpocrates permits data store, share, and access operations to be recorded in the audit log without leaking sensitive information (e.g., data identifier, user identity), while permitting the validity of data operations to be publicly verifiable. Harpocrates makes use of blockchain techniques to achieve immutability and avoid a single point of failure, while cryptographic zero-knowledge proofs are harnessed for confidentiality and public verifiability. We analyze the security of our proposed technique and prove that it achieves non-malleability and indistinguishability. We fully implemented Harpocrates and evaluated its performance on a real blockchain system (i.e., Hyperledger Fabric) deployed on a commodity platform (i.e., Amazon EC2). Experimental results demonstrated that Harpocrates is highly scalable and achieves practical performance.

Daniel Kang, Tatsunori Hashimoto, Ion Stoica, Yi Sun

Over the past few years, AI methods of generating images have been increasing in capabilities, with recent breakthroughs enabling high-resolution, photorealistic "deepfakes" (artificially generated images with the purpose of misinformation or harm). The rise of deepfakes has potential for social disruption. Recent work has proposed using ZK-SNARKs (zero-knowledge succinct non-interactive argument of knowledge) and attested cameras to verify that images were taken by a camera. ZK-SNARKs allow verification of image transformations non-interactively (i.e., post-hoc) with only standard cryptographic hardness assumptions. Unfortunately, this work does not preserve input privacy, is impractically slow (working only on 128$\times$128 images), and/or requires custom cryptographic arguments. To address these issues, we present zk-img, a library for attesting to image transformations while hiding the pre-transformed image. zk-img allows application developers to specify high level image transformations. Then, zk-img will transparently compile these specifications to ZK-SNARKs. To hide the input or output images, zk-img will compute the hash of the images inside the ZK-SNARK. We further propose methods of chaining image transformations securely and privately, which allows for arbitrarily many transformations. By combining these optimizations, zk-img is the first system to be able to transform HD images on commodity hardware, securely and privately.

Yongbo Jiang, Gongxue Sun, Tao Feng

With the increasing value of various kinds of data in the era of big data, the demand of different subjects for data transactions has become more and more urgent. In this paper, a blockchain-based data transaction protection scheme is proposed to realize the secure transaction sharing among data. This paper carries out the following work: by analyzing the existing data transaction models, we find the data security and transaction protection problems, establish a third-party-free data transaction platform using blockchain, protect users’ data security by combining AES and improved homomorphic encryption technology, and upload the encrypted data to the Interplanetary File System (IPFS) for distributed storage. Finally, we use the powerful functions of the IPFS, combined with inadvertent transmission protocol, two-way authentication, zero-knowledge proof, and other security verification for data transactions. The security analysis proves that this scheme has higher security despite the time overhead, and we will continue to optimize the scheme to improve efficiency in the future.

Eric Allender, John Gouwar, Shuichi Hirahara, Caleb Robelle

No abstract is available for this record.

Carsten Baum, Robin Jadoul, Emmanuela Orsini, Peter Schöll · 5 authors

Zero-Knowledge protocols have increasingly become both popular and practical in recent years due to their applicability in many areas such as blockchain systems. Unfortunately, public verifiability and small proof sizes of zero-knowledge protocols currently come at the price of strong assumptions, large prover time, or both, when considering statements with millions of gates. In this regime, the most prover-efficient protocols are in the designated verifier setting, where proofs are only valid to a single party that must keep a secret state.

Arantxa Zapico, Vitalik Buterin, Dmitry Khovratovich, Mary Maller · 6 authors

We present position-hiding linkability for vector commitment schemes: one can prove in zero knowledge that one or m values that comprise commitment \cm all belong to the vector of size N committed to in \com. Our construction \textsfCaulk can be used for membership proofs and lookup arguments and outperforms all existing alternatives in prover time by orders of magnitude.

Tim Güneysu, Philip Hodges, Georg Land, Mike Ounsworth · 6 authors

Certificate authorities in public key infrastructures typically require entities to prove possession of the secret key corresponding to the public key they want certified. While this is straightforward for digital signature schemes, the most efficient solution for public key encryption and key encapsulation mechanisms (KEMs) requires an interactive challenge-response protocol, requiring a departure from current issuance processes. In this work we investigate how to non-interactively prove possession of a KEM secret key, specifically for lattice-based KEMs, motivated by the recently proposed KEMTLS protocol which replaces signature-based authentication in TLS 1.3 with KEM-based authentication. Although there are various zero-knowledge (ZK) techniques that can be used to prove possession of a lattice key, they yield large proofs or are inefficient to generate. We propose a technique called verifiable generation, in which a proof of possession is generated at the same time as the key itself is generated. Our technique is inspired by the Picnic signature scheme and uses the multi-party-computation-in-the-head (MPCitH) paradigm; this similarity to a signature scheme allows us to bind attribute data to the proof of possession, as required by certificate issuance protocols. We show how to instantiate this approach for two lattice-based KEMs in Round 3 of the NIST post-quantum cryptography standardization project, Kyber and FrodoKEM, and achieve reasonable proof sizes and performance. Our proofs of possession are faster and an order of magnitude smaller than the previous best MPCitH technique for knowledge of a lattice key, and in size-optimized cases can be comparable to even state-of-the-art direct lattice-based ZK proofs for Kyber. Our approach relies on a new result showing the uniqueness of Kyber and FrodoKEM secret keys, even if the requirement that all secret key components are small is partially relaxed, which may be of independent interest for improving efficiency of zero-knowledge proofs for other lattice-based statements.

Lorenzo Grassi, Dmitry Khovratovich, Reinhard Lüftenegger, Christian Rechberger · 6 authors

We propose a new hash function Reinforced Concrete, which is the first generic purpose hash that is fast both for a zero-knowledge prover and in native x86 computations. It is suitable for a various range of zero-knowledge proofs and protocols, from set membership to generic purpose verifiable computation. Being up to 15x faster than its predecessor Poseidon hash, Reinforced Concrete inherits security from traditional time-tested schemes such as AES, whereas taking the zero-knowledge performance from a novel and efficient decomposition of a prime field into compact buckets.

Sanjam Garg, Abhishek Jain, Zhengzhong Jin, Yinuo Zhang

We study the problem of constructing succinct zero knowledge proof systems for floating point computations. The standard approach to handle floating point computations requires conversion to binary circuits, following the IEEE-754 floating point standard. This approach incurs a poly(w) overhead in prover efficiency for computations with w-bit precision, resulting in very high prover runtimes -- already the key bottleneck in the design of succinct arguments. We make the following contributions: -We propose a new model for verifying floating point computations that guarantees approximate correctness w.r.t. a relative error bound. This model is inspired by numerical analysis, and is very meaningful for applications such as machine learning and scientific computing. -Using this model, we present a general method for constructing succinct zero-knowledge proofs for floating point computations starting from existing public-coin "commit-and-prove'' systems. For computations with w-bit precision, our approach incurs only a log(w) overhead in prover running time. Our compiler nearly preserves (up to a factor of 2) the communication complexity of the underlying protocol, and requires sub-linear verification time. The resulting proof can be made non-interactive in the random oracle model. Concretely, our scheme is ~57x faster than the method following IEEE standard exactly [35] for 32-bit floating point computations. Central to our main result, and of independent interest, is a new batch range proof system in standard prime order groups that does not rely on bit decomposition.

Ning Luo, Timos Antonopoulos, William R. Harris, Ružica Piskač · 6 authors

Zero-knowledge (ZK) protocols enable one party to prove to others that it knows a fact without revealing any information about the evidence for such knowledge. There exist ZK protocols for all problems in NP, and recent works developed highly efficient protocols for proving knowledge of satisfying assignments to Boolean formulas, circuits and other NP formalisms. This work shows an efficient protocol for the converse: proving formula unsatisfiability in ZK (when the prover posses a non-ZK proof). An immediate practical application is efficiently proving safety of secret programs.

Matteo Campanelli, Dario Fiore, Semin Han, Jihye Kim · 6 authors

Cryptographic accumulators are a common solution to proving information about a large set S. They allow one to compute a short digest of S and short certificates of some of its basic properties, notably membership of an element. Accumulators also allow one to track set updates: a new accumulator is obtained by inserting/deleting a given element. In this work we consider the problem of generating membership and update proofs for \em batches of elements so that we can succinctly prove additional properties of the elements (i.e., proofs are of constant size regardless of the batch size), and we can preserve privacy. Solving this problem would allow obtaining blockchain systems with improved privacy and scalability.

Dario Fiore, Ida Tucker

We study the problem of privacy-preserving proofs on streamed authenticated data. In this setting, a server receives a continuous stream of data from a trusted data provider, and is requested to prove computations over the data to third parties in a correct and private way. In particular, the third party learns no information on the data beyond the validity of claimed results. A challenging requirement here, is that the third party verifies the validity with respect to the specific data authenticated by the provider, while communicating only with the server. This problem is motivated by various application areas, ranging from stock-market monitoring and prediction services; to the publication of government-ran statistics on large healthcare databases. All of these applications require a reliable and scalable solution, in order to see practical adoption.

Shravan Srinivasan, Ioanna Karantaidou, Foteini Baldimtsi, Charalampos Papamanthou

An accumulator is a cryptographic primitive that allows a prover to succinctly commit to a set of values while being able to provide proofs of (non-)membership. A batch proof is an accumulator proof that can be used to prove (non-)membership of multiple values simultaneously.

Wenjun Zhu, Yan Li, Wensheng Wang, Jinhong Zhu · 5 authors

In recent years, with 5G and other key technology breakthroughs, IoT technology is accelerating penetration into various industries, and the era of Internet of Everything is coming. However, while the industry is promoting the rapid development of industrial IoT, IoT security issues are also coming up. Based on this, this paper proposes a data privacy protection method for the smart IoT platform, which first adopts zero-knowledge identity proof technology to complete the identity access authentication of a large number of IoT terminal devices; then the data is downscaled and aggregated in the intermediate data collection device, and then the processed data is added to the noise based on Laplace distribution, and finally the data is transmitted to the main server, thus realizing the smart IoT platform Data privacy protection in the process of data transmission.

Linjian Hong, Kai Zhang, Junqing Gong, Haifeng Qian

No abstract is available for this record.

Thomas Loruenser, Florian Wohner, Stephan Krenn

The assignment problem is an essential problem in many application fields and frequently used to optimize resource usage. The problem is well understood and various efficient algorithms exist to solve the problem. However, it was unclear what practical performance could be achieved for privacy-preserving implementations based on multiparty computation (MPC) by leveraging more efficient solution strategies than MPC-based generic simplex solvers for linear programs. We solve this question by implementing and comparing different optimized MPC algorithms to solve the assignment problem for reasonable problem sizes. Our empirical approach revealed various insights to MPC-based optimization and we measured a significant (50x) speed-up compared to the known simplex-based approach. Furthermore, we also study the overhead introduced by making the results publicly verifiable by means of non-interactive zero-knowledge proofs. By leveraging modern proof systems we also achieve significant speed-up for proof and verification times compared to the previously proposed approaches as well as compact proof sizes. Our research was motivated by a real-world use case, based on detailed discussions with representative stakeholders from the aviation industry.

Manish Kumar, B Annappa, Likewin Thomas, Sourav Kanti Addya · 5 authors

The ability to voice one&s;s opinion is the strong foothold which Democracy declares to provide. Amongst all the other mechanisms, Voting constitutes the major tool to gather and summarize people&s;s opinion. Numerous schemes and protocols based on strong cryptography and using the advantages of the prevalent technologies have been proposed and implemented. The inherent lack of a strong framework or consolidated building block to support the same has not been addressed or is in its infancy. Many alternatives are being considered, and in our opinion, the most promising technology in this regard is the evolution of Blockchain. Using blockchain technology we have proposed a scheme for an E-voting process. This would help to overcome the limitations of transparent voting process, votes summarization/counting. All these are at a low workload on the admin in the voting process. Our proposed scheme provides Anonymity to Voters wherein no other person will be able to link the voters vote to a voter. This unlikability is provided using the concept of Non-Interactive Zero Knowledge Proofs on the Blockchain. A public-key cryptosystem is what provides votes privacy. The proposed protocol aims to provide Anonymity of voters, with privacy of votes and results in a transparent and secure Election

Salvatore Pedone, Adriano Fagiolini

This brief addresses the robust lateral control problem for self-driving racecars. It proposes a discrete-time estimation and control solution consisting of a delayed unknown input-state observer (UIO) and a robust tracking controller. Based on a nominal vehicle model, describing its motion with respect to a generic desired trajectory and requiring no information about the surrounding environment, the observer reconstructs the total force disturbance signal, resulting from imperfect knowledge of the time-varying tire-road interface characteristics, presence of other vehicles nearby, wind gusts, and other model uncertainty. Then, the controller actively compensates the estimated force and asymptotically steers the tracking error to zero. The brief also presents a closed-loop stability proof of the method, ensuring perfect asymptotic estimation and tracking by the controlled vehicle. The proposed solution advantageously needs no a-priori information about the total disturbance boundedness, additional variables to model uncertainty, or observer parameters to be tuned. Its effectiveness and superiority to existing methods are studied in theory and shown in simulations where a full racecar model, based on the vehicle dynamics blockset, is required to track aggressive maneuvers. Through a faster and more accurate disturbance estimation, the solution robustly ensures better dynamic responses even with measurement noise.

Cheng Huang, Wei Wang, Dongxiao Liu, Rongxing Lu · 5 authors

It is well known that auto insurance companies (ICs) use personalized car insurance (PCI) to continuously track drivers' behavior to determine their auto premiums. However, drivers inevitably have concerns about the transparency of data collection/processing and the potential privacy leakage. In this paper, we propose a new PCI scheme to achieve privacy preservation and transparency with the assistance of a consortium blockchain. Specifically, a blockchain is first established by a group of consortium members, and each IC can deploy insurance contracts on the blockchain to support public verification of data collection/processing and thus fulfill the transparency requirement. Then a verifiable and privacy-preserving driving behavior evaluation protocol is designed by tailoring partially homomorphic encryption and zero-knowledge proof techniques. Drivers can use the protocol to interact with ICs through the contracts, and ICs can learn drivers' behavior and set corresponding auto premiums by analyzing encrypted driving data. Furthermore, a third-party auditor (TPA) is authorized by drivers and ICs to audit encrypted driving data on the contracts and resist fraud attacks. We model the contract-based auditing as a recursive inspection game where TPA can minimize the number of audits to detect data fraud and penalize malicious drivers according to Nash equilibrium. Therefore, the proposed PCI scheme can guarantee that most of the collected driving data are not biased. Formal simulation-based security analysis is given to prove the security of the proposed scheme, and a proof-of-concept prototype is also developed on an open-source blockchain to demonstrate the feasibility.

Jin Wang, Wei Ou, Osama Alfarraj, Amr Tolba · 6 authors

Since transactions in blockchain are based on public ledger verification, this raises security concerns about privacy protection. And it will cause the accumulation of data on the chain and resulting in the low efficiency of block verification, when the whole transaction on the chain is verified. In order to improve the efficiency and privacy protection of block data verification, this paper proposes an efficient block verification mechanism with privacy protection based on zero-knowledge proof (ZKP), which not only protects the privacy of users but also improves the speed of data block verification. There is no need to put the whole transaction on the chain when verifying block data. It just needs to generate the ZKP and root hash with the transaction information, then save them to the smart contract for verification. Moreover, the ZKP verification in smart contract is carried out to realize the privacy protection of the transaction and efficient verification of the block. When the data is validated, the buffer accepts the complete transaction, updates the transaction status in the cloud database, and packages up the chain. So, the ZKP strengthens the privacy protection ability of blockchain, and the smart contracts save the time cost of block verification.

Guanjun Zhao, Lizhong Jia, Jie Xu, Chang Liu · 6 authors

With the advent of the era of power trading, how to balance the interests of all parties has become the key to the development of electric power information. The Multi-Microgrid model has gradually become an important part of power trading due to its reliability and efficiency, but how to balance the profit game among the Multi-Microgrid has gradually become a difficult problem for market development. In view of the distributed transaction environment of multi-micro network, we propose to use blockchain technology for multi-party transaction, use Stackelberg game model to achieve the best balance of interests of all participants, and zero-knowledge proof combined with secret sharing scheme is used to achieve effective access control in transactions. We simulate and test the performance indexes of the scheme, and the results show that our scheme is feasible.

Matthieu Rambaud, Andrei Tonkikh, Mark Abspoel

To be competitive with centralized applications, consensus protocols in blockchains must provide minimal latency while being able to scale to thousands of participants in order to preserve a high level of decentralization. A common way to minimize latency is to augment a consensus protocol with a fast track, which ensures that a decision is reached in just a couple of message delays in favorable conditions. However, it is a challenging task to preserve safety and good performance when these favorable conditions do not hold. To the best of our knowledge, all existing Byzantine fault-tolerant consensus protocols with fast tracks require view change protocols with quadratic authenticator complexity. In this paper, we provide the first solution to Byzantine consensus with fast track with a linear view change. The protocol incurs no asymptotic overhead over the baseline while reducing the latency in favorable conditions by a factor of 2. Our construction is based on a novel type of cryptographic proofs, which we call Proofs of Exclusivity (or PoE for short), which may be of independent interest. While our protocol for constructing a PoE comes at no extra costs in latency or asymptotic complexities, it does require some extra computation. To make sure that it does not impair the overall performance, we also show how to apply accountability and proofs of misbehavior in order to reduce to zero the overhead incurred by the computation of a PoE. More precisely, our mechanism guarantees that whenever this overhead is not zero, then automatically honest participants obtain a publicly verifiable proof that a well-identified malicious participant openly misbehaved. In this case, the overhead of computing a few extra threshold signatures for the Proof of Exclusivity can be seen as a relatively small price to get rid of a malicious participant.

Moyixi Lei, Shuangyin Liu, Na Luo, Xinting Yang · 5 authors

Traceability systems have changed the way food safety is managed and data is stored. Blockchain tracking services now provide customers with an infrastructure that allows them to easily access data online. However, there are limitations to these new capabilities, such as a lack of transparency and the existence of privacy and security challenges. Additionally, as the need for more agile, private, and traceability secure data solutions continues to grow exponentially, rethinking the current structure of blockchain agricultural traceability is mission-critical for a country. By leveraging and building upon blockchain's unique attributes, including tamper-evident, security hash crypto-data, and distributed ledger, we have proposed a prototype that allows traceability data to be reliably stored via blockchain while simultaneously being secured, with completeness auditing to enhance credibility. The result, the trusted auditing chain (TA chain), is a flexible solution that assures data security and solves challenges such as scalability and privacy-preserving. The TA chain works through Schnorr-style non-interactive Zero-knowledge proof to support security automatical choose privacy augmented. In addition, The TA chain can audit more than 1000 transactions within 1ms, and its error stabilizes below the 250 μs, which proves a security and fair traceability system to assure that data is distributed and reliably, and provably audited.