Classical and contemporary distributed consensus protocols, may they be for binary agreement, state machine replication, or blockchain consensus, require all protocol participants in a peer-to-peer system to agree on exactly the same information as part of the consensus payload. Although this model of consensus is extensively studied, and is useful for most consensus based decentralized applications, it falls short of defining correct distributed systems which mandate participant credential based privileged visibility into the consensus payload, through the consensus protocol itself. We introduce a new paradigm for distributed consensus, called functional blockchain consensus. Functional blockchain consensus allows each blockchain protocol participant to agree on some distinct sub-information of the list of transactions, as a function of the credentials of the participant in the blockchain system, instead of agreeing on the entire list of transactions. We motivate two adversary models, one with a standard crash-fault adversary and another with a novel rational-fault adversary, to compromise functional blockchain consensus. We then present two versions of a blockchain protocol called SightSteeple, that achieves functional blockchain consensus in the said fault models. SightSteeple relies on a novel combination of standard blockchain consensus and functional encryption, among other primitives, to achieve its goals of correctness. Finally, we discuss practical uses of functional blockchain consensus based asymmetric distributed ledgers, and motivate off-shoot constructions that can result from this new consensus paradigm.
Blockchain technology is one of the most popular information technologies at present, and its security features are realized through various cryptographic tools. Zero-knowledge proofs are such a tool that can increase data security and improve users’ privacy, and zero-knowledge proof schemes constructed with polynomial commitments have advantages in terms of verification time and proof size. Benefiting from the development of blockchain technology, zero-knowledge proof has also ushered in rapid development. This paper analyzes the research status of zero-knowledge proof schemes based on polynomial commitment construction, and introduces the construction and security of polynomial commitments. Finally, blockchain and some other potential commitment schemes that can be used for zero-knowledge proofs and blockchain construction are introduced as future research directions and engineering applications.
Rodrigo Dutra Garcia, Gowri Ramachandran, Jó Ueyama
Smart contracts allow application developers to automate business processes through a decentralized computation architecture. Contemporary blockchain platforms such as Ethereum and Hyperledger Fabric offer support for smart contracts through consensus mechanisms such as Proof-of-Work (PoW) or other types of transaction validation and ordering services. This article exploits smart contracts in the Byzantine Fault Tolerant (BFT) blockchain platforms. In particular, we explore Tendermint and Hyperledger Besu, BFT blockchain platforms, and apply them to a decentralized e-prescription case study to evaluate their effectiveness. We adopt Hyperledger Besu and Tendermint in this research, given that both are BFT-based blockchains. Also, it is noteworthy that smart contracts in BFT blockchain platforms such as Tendermint are not well established and not widely adopted yet. Our article empirically evaluates the performance of smart contracts in Tendermint and Hyperledger Besu using a decentralized medical prescription case study and compares their results with Ethereum, a PoW blockchain. Our results demonstrate that BFT blockchain platforms are efficient for multistakeholder applications such as e-prescription and supply chains. To the best of our knowledge, this is the first study investigating the implementation of smart contracts in BFT blockchain platforms, such as Tendermint and Hyperledger Besu.
Smart contracts on the Ethereum blockchain greatly benefit from cutting-edge analysis techniques and pose significant challenges. A primary challenge is the extremely low-level representation of deployed contracts. We present Elipmoc, a decompiler for the next generation of smart contract analyses. Elipmoc is an evolution of Gigahorse, the top research decompiler, dramatically improving over it and over other state-of-the-art tools, by employing several high-precision techniques and making them scalable. Among these techniques are a new kind of context sensitivity (termed “transactional sensitivity”) that provides a more effective static abstraction of distinct dynamic executions; a path-sensitive (yet scalable, through path merging) algorithm for inference of function arguments and returns; and a fully context sensitive private function reconstruction process. As a result, smart contract security analyses and reverse-engineering tools built on top of Elipmoc achieve high scalability, precision and completeness. Elipmoc improves over all notable past decompilers, including its predecessor, Gigahorse, and the state-of-the-art industrial tool, Panoramix, integrated into the primary Ethereum blockchain explorer, Etherscan. Elipmoc produces decompiled contracts with fully resolved operands at a rate of 99.5% (compared to 62.8% for Gigahorse), and achieves much higher completeness in code decompilation than Panoramix—e.g., up to 67% more coverage of external call statements—while being over 5x faster. Elipmoc has been the enabler for recent (independent) discoveries of several exploitable vulnerabilities on popular protocols, over funds in the many millions of dollars.
Yeonouk Chu, Jae‐Ho Lee, Sung-Joong Kim, Hyun-Joong Kim · 6 authors
Due to the growth of the internet and communication technologies, electronic financial systems are becoming popular. Physical cash is losing its preeminence, and digital numbers on computers represent money. However, electronic financial systems, mostly operated by private entities, have defects to be compensated for, such as high charges for using the system, security issues, and the problem of exclusion. As a solution, many countries around the world are considering central bank digital currency. For central bank digital currency to be utilized as a national legal tender, it must be universal and accessible regardless of time and place, similar to physical cash. Therefore, offline payment functions that extend the accessibility of central bank digital currency are becoming attractive. However, due to the characteristics of the electronic financial system, central bank digital currency is vulnerable to possible malicious behaviors in offline situations, such as blackouts and system shutdowns. This paper reviews research studies that deal with security matters related to the offline payment function of central bank digital currency. Offline payment solutions, including central bank digital currency and other electronic financial systems, such as electronic cash and cryptocurrency, are reviewed, and supplemental methods to improve the offline payment solutions of central bank digital currency based on trusted execution environment devices are suggested.
Smart contracts are cryptographic protocols that are enforced without a judiciary. Smart contracts are used occasionally in Bitcoin and are prevalent in Ethereum. Public quantum money improves upon cash we use today, yet the current constructions do not enable smart contracts. In this work, we define and introduce quantum payment schemes, and show how to implement prudent contracts -- a non-trivial subset of the functionality that a network such as Ethereum provides. Examples discussed include: multi-signature wallets in which funds can be spent by any 2-out-of-3 owners; restricted accounts that can send funds only to designated destinations; and "colored coins" that can represent stocks that can be freely traded, and their owner would receive dividends. Our approach is not as universal as the one used in Ethereum since we do not reach a consensus regarding the state of a ledger. We call our proposal prudent contracts to reflect this. The main building block is either quantum tokens for digital signatures (Ben-David and Sattath QCrypt'17, Coladangelo et al. Crypto'21), semi-quantum tokens for digital signatures (Shmueli'22) or one-shot signatures (Amos et al. STOC'20). The solution has all the benefits of public quantum money: no mining is necessary, and the security model is standard (e.g., it is not susceptible to 51\% attacks, as in Bitcoin). Our one-shot signature construction can be used to upgrade the Bitcoin network to a quantum payment scheme. Notable advantages of this approach are: transactions are locally verifiable and without latency, the throughput is unbounded, and most importantly, it would remove the need for Bitcoin mining. Our approach requires a universal large-scale quantum computer and long-term quantum memory; hence we do not expect it to be implementable in the next few years.
The cloud computing technology has emerged, developed, and matured in recent years, consequently commercializing remote outsourcing storage services. An increasing number of companies and individuals have chosen the cloud to store their data. However, accidents, such as cloud server downtime, cloud data loss, and accidental deletion, are serious issues for some applications that need to run around the clock. For some mission and business-critical applications, the continuous availability of outsourcing storage services is also necessary to protect users' outsourced data during downtime. Nevertheless, ensuring the continuous availability of data in public cloud data integrity auditing protocols leads to data privacy issues because auditors can obtain the data content of users by a sufficient number of storage proofs. Therefore, protecting data privacy is a burning issue. In addition, existing data integrity auditing schemes that rely on semi-trusted third-party auditors have several security problems, including single points of failure and performance bottlenecks. To deal with these issues, we propose herein a blockchain-based continuous data integrity checking protocol with zero-knowledge privacy protection. We realize a concrete construction by using a verifiable delay function with high efficiency and proof of retrievability, and prove the security of the proposal in a random oracle model. The proposed construction supports dynamic updates for the outsourced data. We also design smart contracts to ensure fairness among the parties involved. Finally, we implement the protocols, and the experimental results demonstrate the efficiency of the proposed protocol.
Nowadays, Blockchain-based rating/review systems are gaining popularity as a backbone for recommender systems due to the inherent cryptographically secured decentralised architecture, immutability, user anonymity, and inclusion of smart contracts. However, the existing Blockchain-based rating/review systems address resistance to the standard attacks, i.e. collusion attack, user threatening, and unfair rating. Still, they do not present security analyses of smart contracts that may result in substantial threats to the users of the systems. This manuscript presents an in-depth study of twelve publicly available security analysis tools and standard vulnerabilities in smart contracts and reviews. The experimental setup uses a two-step approach for selecting the security analysis tool. The first step identifies the seven tools their proposers or independent researchers have compared, and the second step proposes a new method for selecting tools based on continuous improvement. Our experimental results show security issues in 51.72% of the analysed smart contracts of four Blockchain-based rating/review systems. 6.67% of vulnerable smart contracts exhibit high-level severity threats that raise an alarming condition for the current state of system developments.
Aditya Pribadi Kalapaaking, Ibrahim Khalil, Mohammad Saidur Rahman, Mohammed Atiquzzaman · 6 authors
This article proposes a blockchain-based federated learning (FL) framework with Intel Software Guard Extension (SGX)-based trusted execution environment (TEE) to securely aggregate local models in Industrial Internet-of-Things (IIoTs). In FL, local models can be tampered with by attackers. Hence, a global model generated from the tampered local models can be erroneous. Therefore, the proposed framework leverages a blockchain network for secure model aggregation. Each blockchain node hosts an SGX-enabled processor that securely performs the FL-based aggregation tasks to generate a global model. Blockchain nodes can verify the authenticity of the aggregated model, run a blockchain consensus mechanism to ensure the integrity of the model, and add it to the distributed ledger for tamper-proof storage. Each cluster can obtain the aggregated model from the blockchain and verify its integrity before using it. We conducted several experiments with different CNN models and datasets to evaluate the performance of the proposed framework.
Komal Gilani, Fariba Ghaffari, E. Bertin, Noël Crespi
In centralized infrastructures, users are not capable of authenticating themselves, in identity management systems, beyond their application’s domain. Users are forced to trust their service providers for identification and data management. Such solutions have experienced large-scale data breaches and are cumbersome for users to remember the credentials for multiple sites. Furthermore, users have very little control over their data. The concept of decentralized identity has raised the possibility of better managing these concerns. It allows users to share only the relevant part of their personal information with a service provider to verify their digital identity. We propose OrgID, a decentralized identity and user-centric data management platform including identity registration and authorization procedures. Our approach supports self-sovereign identity architecture leveraged by blockchain. This method consists of a one-time proof-verification mechanism that facilitates the secure access and credibility of digital information. Moreover, users can maintain their identities associated with specific attributes and rely on a proof mechanism using smart contracts. It deploys a platform where user registration and authorization no longer involve a central service provider. We implemented the proposed solution using smart contracts on a private Ethereum blockchain. We further analyzed the performance of these processes regarding the system’s scalability to evaluate how they manage latency and the number of users. The results state that the system is highly scalable to manage a large number of users and the system’s latency is adjustable based on the application needs.
Storage is a promising application for permission-less blockchains. Before blockchain, cloud storage was hosted by a trusted service provider. The centralized system controls the permission of the data access. In web3, users own their data. Data must be encrypted in a permission-less decentralized storage network, and the permission control should be pure cryptographic. Proxy re-encryption (PRE) is ideal for cryptographic access control, which allows a proxy to transfer Alice’s ciphertext to Bob with Alice’s authorization. The encrypted data are stored in several copies for redundancy in a permission-less decentralized storage network. The redundancy suffers from the outsourcing attack. The malicious resource provider may fetch the content from others and respond to the verifiers. This harms data integrity security. Thus, proof-of-replication (PoRep) must be applied to convince the user that the storage provider is using dedicated storage. PoRep is an expensive operation that encodes the original content into a replication. Existing PRE schemes cannot satisfy PoRep, as the cryptographic permission granting generates an extra ciphertext. A new ciphertext would result in several expensive replication operations. We searched most of the PRE schemes for the combination of the cryptographic methods to avoid transforming the ciphertext. Therefore, we propose a new PRE scheme. The proposed scheme does not require the proxy to transfer the ciphertext into a new one. It reduces the computation and operation time when allowing a new user to access a file. Furthermore, the PRE scheme is CCA (chosen-ciphertext attack) security and only needs one key pair.
There are significant data privacy implications associated with Electronic Health Records (EHRs) sharing among various untrusted healthcare entities. Recently, a blockchain-based EHRs sharing system has provided many benefits. Decentralization, anonymity, unforgeability, and verifiability are all unique properties of blockchain technology. In this paper, we propose a secure, blockchain-based EHR sharing system. After receiving the data owner’s authorization, the data requester can use the data provider’s keyword search to discover relevant EHRs on the EHR consortium blockchain and obtain the re-encryption ciphertext from the proxy server. To attain privacy, access control and data security, the proposed technique uses asymmetric searchable encryption and conditional proxy re-encryption. Likewise, proof of permission serves in consortium blockchains as the consensus method to ensure the system’s availability. The proposed protocol can achieve the specified security goals, according to the security analysis. In addition, we simulate basic cryptography and put the developed protocol into practice on the Ethereum platform. The analysis results suggest that the developed protocol is computationally efficient.
The lack of data outsourcing in healthcare management systems slows down the intercommunication and information sharing between different entities. A standard solution is outsourcing the electronic health record (EHR) to a cloud service provider (CSP). The outsourcing of the EHR should be performed securely without compromising the CSP functionalities. Searchable encryption would be a viable approach to ensure the confidentiality of the data without compromising searchability and accessibility. However, most existing searchable encryption solutions use centralised architecture. These systems have trust issues as not all the CSPs are fully trusted or honest. To address these problems, we explore blockchain technology with smart contract applications to construct a decentralised system with auditable yet immutable data storage and access. First, we propose a blockchain-based searchable encryption scheme for EHR storage and updates in a decentralised fashion. The proposed scheme supports confidentiality of the outsourced EHR, keyword search functionalities, verifiability of the user and the server, storage immutability, and dynamic updates of EHRs. Next, we implement a prototype using JavaScript and Solidity on the Ethereum platform to demonstrate the practicality of the proposed solution. Finally, we compare the performance and security of the proposed scheme against existing solutions. The result indicates that the proposed scheme is practical while providing the desired security features and functional requirements.
Information sharing has become an important application in modern supply chain management systems with business technology development. Because traditional supply chain information systems have problems such as easy data tampering, low information transparency, and interaction delays, blockchain has been taken consideration into supply chain information sharing research. Furthermore, blockchain technology is expected to provide decentralized supply chain information sharing solutions to enhance security, availability, and transparency. However, with the in-depth study of the application of blockchain technology in supply chain information sharing, people have found that the data stored publicly in the blockchain are still threatened by privacy leakage. In addition, due to the openness and accessibility of the blockchain, the lack of fine-grained access control is also apparent. In order to improve the security of data, we propose a novel privacy-preserving multiauthority attribute-based access control scheme for secure blockchain-based information sharing in a supply chain. In this scheme, blockchain stores encrypted supply chain information on distributed nodes. Multiple attribute authorities manage different attributes of users to achieve fine-grained access control and flexible authorization. Even if some attribute authorities fail, the user’s private key will not be leaked. In user secret key generation, we adopt an anonymous key generation protocol to realize the secure distribution of user keys by the attribute authorities. Furthermore, in order to meet the protection of communication privacy between blockchain nodes, properties of policy hiding and identity hiding are considered. Finally, we design experiments to analyze the performance of our scheme, including secret key sizes and running time of encryption and decryption.
The integration of information systems and physical systems is the development trend of today’s manufacturing industry. Intelligent manufacturing is a new model of manufacturing, based on advanced manufacturing technology with human–machine–material collaboration. Internet of Things technology is the core technology of intelligent manufacturing, and access control technology is one of the main measures to ensure the security of the IoT. In view of the problem that the existing IoT access control model does not support distributed and fine-grained dynamic access control, this paper uses the characteristics of blockchain, such as decentralization and non-tampering, combined with the attribute-based access control (ABAC) method, to propose a distributed access control method, applicable to the IoT environment in the process of intelligent manufacturing. This paper describes a fine-grained access control policy by defining the access control attribute values in a formal language, which supports complex logic operations in the policy and enhances the expressiveness of the model. Distributed access control decision making, using smart contracts for blockchain, improves the decision-making efficiency of the access control model, increases the post-facto audit of the access control behavior, and improves the overall security of IoT data protection. The paper concludes with proof of security and a performance analysis, and the experimental results, such as storage and computing overheads, show that this method can provide fine-grained, dynamic, and distributed access control for devices in intelligent manufacturing, ensuring the security and reliability of access control for IoT devices.
With the explosive growth of data, cloud storage has become a widely used storage method. To protect the integrity and availability of data in cloud storage systems, multireplica provable data possession has gradually become a research hotspot. This paper uses smart contracts to replace traditional third-party auditor (TPA) and proposes a noninteractive multireplica provable data possession scheme based on smart contracts, making the verification process public, immutable, traceable, and able to be carried out periodically and automatically. This paper introduces the concept of noninteractivity to reduce the transaction fees caused by the frequent operation of blockchain in the verification process. By stipulating payment rules in the smart contract, we can ensure the fairness of all parties. Finally, we give the correctness proof of the scheme and the security proof in the random oracle model, comparing it with other schemes and verifying the practicability of our scheme through experiments.
Owing to the meteoric rise in the usage of cryptocurrencies, there has been a widespread adaptation of traditional financial applications such as lending, borrowing, margin trading, and more, to the cryptocurrency realm. In some cases, the inherently transparent and unregulated nature of cryptocurrencies leads to attacks on users of these applications. One such attack is frontrunning, where a malicious entity leverages the knowledge of currently unprocessed financial transactions submitted by users and attempts to get its own transaction(s) executed ahead of the unprocessed ones. The consequences of this can be financial loss, inaccurate transactions, and even exposure to more attacks. We propose FIRST, a framework that prevents frontrunning attacks, and is built using cryptographic protocols including verifiable delay functions and aggregate signatures. In our design, we have a federated setup for generating the public parameters of the VDF, thus removing the need for a single trusted setup. We formally analyze FIRST, prove its security using the Universal Composability framework and experimentally demonstrate the effectiveness of FIRST.
Remote voting has become more critical in recent years, especially since the COVID-19 outbreak. Blockchain technology and its benefits such as decentralization, security, and transparency have given rise to proposals for blockchain-based voting systems. However, the traceability of blockchain transactions violates voter anonymity in existing proposals. Besides, transaction costs also need to be considered. Solutions that may cause repeated elections should be avoided for a low-cost scalable voting system. In this work, we propose ElectAnon, a blockchain-based, self-tallying, and ranked-choice voting protocol focusing on anonymity, robustness, and scalability. ElectAnon achieves anonymity by enabling voters to register with identity commitments and cast their votes via zero-knowledge proofs. Robustness is realized by removing the direct control of the authorities in the voting process by using timed-state machines. Each voter encodes the ballot into a single integer and blinds the vote off-chain while making the verification on-chain. This makes the protocol infinitely scalable in the number of voters. ElectAnon is also a solution for governance in Decentralized Autonomous Organizations (DAO): It includes a candidate proposal module and an algorithm-agnostic mechanism to plug-in different tallying methods easily. The Merkle forest extension is proposed for conducting even more trustless elections. ElectAnon is implemented with smart contracts based on Ethereum Virtual Machine (EVM) and a zero-knowledge gadget, Semaphore. The implementation also includes two different sophisticated tallying methods, Borda Count and Tideman. Experimental results show that a 40-voter and 10-candidate election can be implemented with the gas consumption reduced up to 89% compared to previous works. While other studies could not exceed a 25,000-voter setup, ElectAnon has been observed to run safely for 1,000,000 voters. The implementation can be found at https://github.com/ceyonur/electanon .
José L. Muñoz, Marta Bellés, Miguel Isabel, Albert Rubio · 5 authors
A zero-knowledge (ZK) proof guarantees that the result of a computation is correct while keeping part of the computation details private. Some ZK proofs are tiny and can be verified in short time, which makes them one of the most promising technologies for solving two key aspects: the challenge of enabling privacy to public and transparent distributed ledgers and, enhancing the scalability limitations of distributed ledgers. Most practical ZK systems require the computation to be expressed as an arithmetic circuit that is encoded as a set of equations called rank-1 constraint system (R1CS). In this paper, we present \circom, a programming language and a compiler for designing arithmetic circuits that are compiled to R1CS. More precisely, with \circom, programmers can design arithmetic circuits, and the compiler outputs (i) a file with the R1CS description, (ii) \wasm and \cpp programs to efficiently compute all values of the circuit. We also provide an open-source library called \circomlib, with multiple circuit templates. Moreover, \circom can be complemented with \snarkjs, a tool for generating and validating ZK proofs from R1CS. Altogether, our software tools abstract the complexity of the proving mechanisms and provide a friendly interface to model low-level descriptions of arithmetic circuits.
Gang Xu, Shiyuan Xu, Yibo Cao, Fan Yun · 7 authors
In the current E-healthcare scenarios, medical institutions are used to encrypt the information and store it in an Electronic Health Record (EHR) system in order to ensure the privacy of medical information. To realize data sharing, a Public-key Encryption with Keyword Search (PEKS) scheme is indispensable, ensuring doctors search for medical information in the state of ciphertext. However, the traditional PEKS scheme cannot resist the keyword guessing quantum computing attacks, and its security depends on the confidentiality of the secret key. In addition, classical PEKS hand over the search process to a third party, affecting the search results’ accuracy. Therefore, we proposed a postquantum Public-key Searchable Encryption scheme on Blockchain (PPSEB) for E-healthcare scenarios. Firstly, we utilized a lattice-based cryptographic primitive to ensure the security of the search process and achieve forward security to avoid key leakage of medical information. Secondly, we introduced blockchain technology to solve the problem of third-party untrustworthiness in the search process. Finally, through security analysis, we prove the correctness and forward security of the solution in the E-healthcare scenarios, and the comprehensive performance evaluation demonstrates the efficiency of our scheme compared with other existing schemes.
Dan Bogdanov, Joosep Jääger, Peeter Laud, Härmel Nestra · 10 authors
We present ZK-SECREC, a domain-specific language for zero-knowledge (ZK) proofs. We focus on its type system, making the point that this is the most appropriate mechanism for tracking information flows in a statement that is meant to be proved using a zero-knowledge protocol. The appropriateness stems from the necessary distinctions between the two involved parties and between the computations made locally or on top of the protocol. The appropriateness also stems from how the types match with the major steps of typical ZK protocols, including the generation of Common Reference Strings. We compare the type system of ZK-SECREC with those of the previously proposed languages for ZK proofs and privacy-preserving computations, and show how ZK-SECREC handles certain aspects better.
The data outsourcing services provided by cloud storage have greatly reduced the headache of data management for users, but the issue of remote data integrity poses further security concerns and computing burdens. The introduction of a third-party auditor (TPA) frees data owners from the auditing burden and alleviates disputes over the audit results between data owners and cloud storage providers. However, malicious cloud servers may collude with TPAs to deceive users for financial profits. Hiring multiple auditors in a single audit assignment appears to be a method to address the above problem, but the ensuing voting issues need to be further explored. In this paper, we proposed a smart contract-based outsourced data integrity auditing scheme for multiauditor scenarios. Unlike some existing schemes using reputation like factors as their voting weights, auditors in our scheme vote equally and audit as they go, without any maintenance. This mechanism not only frees auditors from trivia not related to the auditing but also avoids the drawbacks of centralization associated with over-high voting weights. The challenge used to check the integrity of the outsourced data is jointly generated by each involved auditor. Any collusion would be detected as long as there exists more than one honest auditor in the audit. We implement and deploy the scheme as Ethereum smart contracts. With the help of blockchain, the entire auditing process is public and transparent. Both the generated data and the obtained results are persisted with immutability, which ensures the traceability of all historical audits. The comprehensive theoretical and experimental analyses demonstrate that our scheme meets the claimed targets with high efficiency and low gas costs.