Blockchain oracles are systems that connect blockchains with the outside world by interfacing with external data providers. They provide decentralized applications with the external information needed for smart contract execution. In this paper, we focus on decentralized price oracles, which are distributed systems that provide exchange rates of digital assets to smart contracts. They are the cornerstone of the safety of some decentralized finance applications such as stable coins or lending protocols. They consist of a network of nodes called oracles that gather information from off-chain sources such as an exchange market's API and feed it to smart contracts. Among the desired properties of a price oracle system are low latency, availability, and low operating cost. Moreover, they should overcome constraints such as having diverse data sources which is known as the freeloading problem or Byzantine failures. In this paper, we define the distributed price oracle problem and present PoWacle, the first asynchronous decentralized oracle protocol that copes with Byzantine behavior.
The continuous production of large-scale data makes data outsourcing computation a trend. In order to ensure that data outsourcing transaction is trusted and fair, it needs the supervision and judgment of a third party. However, the third-party intermediary increases the transaction cost, and there is also subjective unreliability. Smart contracts allow trusted transactions without a third party, which are automatic, traceable and irreversible. Therefore, in this paper, we propose a framework for data outsourcing computation transaction based on the smart contract, in which the transaction is verifiable, fair and privacy protected. In this framework, by improved the replication-based verifiable computation technology, the data in the dataset is evenly distributed to each server, and at least one data in the sub datasets of the adjacent servers is the same, only the results from the duplicate data are verified, so as to implement the verifiable transaction with the low transaction cost. Meanwhile, a punishment mechanism is adopted to solve the fairness of the transaction in the smart contract. In addition, the oblivious transfer protocol is used to implement the privacy protection of transaction data. We deploy the data outsourcing computation transaction framework in the simulation environment of the Ethereum blockchain, and the experimental results show that our proposed scheme is effective and has low overhead. Specifically, the data returned by the server is verifiable, and the data privacy of the client is protected. When the client and servers are dishonest, they will be punished so that the transaction is fair. Moreover, the cost of using the smart contract in transactions is almost negligible.
In recent years, the interest in using wireless communication technologies and mobile devices in the healthcare environment has increased. However, despite increased attention to the security of electronic health records, patient privacy is still at risk for data breaches. Thus, it is quite a challenge to involve an access control system especially if the patientsâ medical data are accessible by users who have diverse privileges in different situations. Blockchain is a new technology that can be adopted for decentralized access control management issues. Nevertheless, different scalability, security, and privacy challenges affect this technology. To address these issues, we suggest a novel Decentralized Self-Management of data Access Control (DSMAC) system using a blockchain-based Self-Sovereign Identity (SSI) model for privacy-preserving medical data, empowering patients with mechanisms to preserve control over their personal information and allowing them to self-grant access rights to their medical data. DSMAC leverages smart contracts to conduct Role-based Access Control policies and adopts the implementation of decentralized identifiers and verifiable credentials to describe advanced access control techniques for emergency cases. Finally, by evaluating performance and comparing analyses with other schemes, DSMAC can satisfy the privacy requirements of medical systems in terms of privacy, scalability, and sustainability, and offers a new approach for emergency cases.
Tom Godden, Ruben De Smet, Christophe Debruyne, Thibaut Vandervelden · 6 authors
Driven by the increased consciousness in data ownership and privacy, zero-knowledge proofs (ZKPs) have become a popular tool to convince a third party of the truthfulness of a statement without disclosing any further information. As ZKPs are rather complex to design, frameworks that transform high-level languages into ZKPs have been proposed. We propose Circuitree, a Datalog reasoner in zero-knowledge. Datalog is a high-level declarative logic language that is generally used for querying. Furthermore, as a logic language, it can also be used to solve logic problems. An application using Circuitree can efficiently generate ZKPs, based on Datalog rules and encrypted data, to prove that a certain conclusion follows from a Datalog ruleset and encrypted input data. Compared to existing frameworks, which generally use their own limited imperative languages, Circuitree uses an existing high-level declarative language. We point out several applications for Circuitree, including EU Digital COVID Certificates and privacy-preserving access control for peer-to-peer (p2p) networks. Circuitreeâs performance is evaluated for access control in a p2p network. First results show that our approach allows for fast proofs and proof verification for this application.
Bitcoin is one of the best-known cryptocurrencies, which captivated researchers with its innovative blockchain structure. Examinations of this public blockchain resulted in many proposals for improvement in terms of anonymity and privacy. Generally used methods for improvement include mixing protocols, ring signatures, zero-knowledge proofs, homomorphic commitments, and off-chain storage systems. To the best of our knowledge, in the literature, there is no study examining Bitcoin in terms of differential privacy, which is a privacy notion coming up with some mechanisms that enable running useful statistical queries without identifying any personal information. In this paper, we provide a theoretical examination of differential privacy in Bitcoin. Our motivation arises from the idea that the Bitcoin public blockchain structure can benefit from differential privacy mechanisms for improved privacy, both making anonymization and privacy breaches by direct queries impossible, and preserving the checkability of the integrity of the blockchain. We first examine the current Bitcoin implementation for four query functions using the differential privacy formulation. Then, we present the feasibility of the utilization of two differential privacy mechanisms in Bitcoin; the noise addition to the transaction amounts and the user graph perturbation. We show that these mechanisms decrease the fraction of the cases violating differential privacy, therefore they can be used for improving anonymity and privacy in Bitcoin. Moreover, we showcase the noise addition to transaction amounts by using IBM Differential Privacy Library. We compare four differential privacy mechanisms for varying privacy parameter values and determine the feasible mechanisms and the parameters.
Md. Rayhan Ahmed, A.K.M. Muzahidul Islam, Swakkhar Shatabda, Salekul Islam
Identity Management System (IDMS) refers to how users or individuals are identified and authorized to use organizational systems and services. Since traditional identity management and authentication systems rely heavily on a trusted central authority, they cannot mitigate the effects of single points of failure. As a decentralized and distributed public ledger in a peer-to- peer (P2P) network, Blockchain (BC) technology has garnered a considerable amount of attention in the field of IDMS in recent years. Through Self-Sovereign Identity (SSI), users can have full authority over their digital identity. Successful implementation of a BC-based IDMS can significantly increase the degree of privacy and security of a userâs SSI. However, the integration of BC-based IMDS to provide a user with SSI is still an unorganized area of research in its early stages of development. This article presents an extensive literature review of state-of-the-art academic publications as well as commercial market offerings regarding the applicability of BC-based SSI solutions. It also provides a detailed preliminary regarding the building blocks of blockchain technology and a progressive roadmap of IDMS solutions. In order to develop an effective BC-based IDMS solution that focuses on securing a userâs SSI, this article outline five essential components of a BC-based IDMS: authentication, integrity, privacy, trust, and simplicity. Furthermore, we perform a security analysis that outlines several types of adversarial threats that can cause potential damage to the BC-based IDMS. We identify and discuss associated issues and challenges by analyzing several notable BC-based IDMS solutions in academic literature. We also highlight potential research gaps and provide future research scope.
Peg solitaire is a very popular traditional single-player board game, known to be NP-complete. In this paper, we present a zero-knowledge proof of knowledge for solutions of peg solitaire instances. Our proof is straightforward, in the sense that it does not use any reduction to another NP-complete problem, and uses the standard design of sigma protocols. Our construction relies on cryptographic commitments, which can be replaced by envelopes to make the protocol physical. As a side contribution, we introduce the notion of isomorphisms for peg solitaire, which is the key tool of our protocol.
Abstract The most widely used Zero-Knowledge (ZK) protocols require provers to prove they know a solution to a computational problem expressed as a Rank-1 Constraint System (R1CS). An R1CS is essentially a system of non-linear arithmetic constraints over a set of signals, whose security level depends on its non-linear part only, as the linear (additive) constraints can be easily solved by an attacker. Distilling the essential constraints from an R1CS by removing the part that does not contribute to its security is important, not only to reduce costs (time and space) of producing the ZK proofs, but also to reveal to cryptographic programmers the real hardness of their proofs. In this paper, we formulate the problem of distilling constraints from an R1CS as the (hard) problem of simplifying constraints in the realm of non-linearity. To the best of our knowledge, it is the first time that constraint-based techniques developed in the context of formal methods are applied to the challenging problem of analysing and optimizing ZK protocols.
Jacco O.G. Krijnen, Manuel M. T. Chakravarty, Gabriele Keller, Wouter Swierstra
Compiler correctness is an old problem, but with the emergence of smart contracts on blockchains that problem presents itself in a new light. Smart contracts are self-contained pieces of software that control (valuable) assets in an adversarial environment; once committed to the blockchain, these smart contracts cannot be modified. Smart contracts are typically developed in a high-level contract language and compiled to low-level virtual machine code before being committed to the blockchain. For a smart contract user to trust a given piece of low-level code on the blockchain, they must convince themselves that (a) they are in possession of the matching source code and (b) that the compiler has correctly translated the source code to the given low-level code. Classic approaches to compiler correctness tackle the second point. We argue that translation certification also squarely addresses the first. We describe the proof architecture of a translation certification framework and demonstrate how we can model the compilation pipeline as a sequence of translation relations. We give a detailed account of such relations for most passes of the Plutus Tx compiler, which we formalised in Coq. This approach facilitates a modular verification methodology and is robust in the face of an evolving compiler implementation.
Nowadays, cloud-based storage systems play a vital role in IoT data storage, processing, and sharing. Despite its contribution, the current cloud-based architecture may cause severe data leakage or jeopardize user privacy. Meanwhile, the cloud-based architecture heavily relies on a trusted third-party auditor (TPA) and runs in a centralized control manner. However, the TPA may not be a completely trustworthy entity, and a single point of failure might cause the centralized system to collapse. Fortunately, with the advent of blockchain technology, the decentralized storage model has gained popularity. A decentralized storage system successfully eradicates the rule of TPA, solves the problem of a single point of failure, and has many advantages over a centralized control architecture, such as low storage prices and high throughput. This study offers a blockchain-based decentralized distributed storage and sharing scheme that provides end-to-end encryption and fine-grained access control. In our proposed IoTChain model, fine-grained permission is based on attribute-based access control (A-BAC) policy by employing the Ethereum blockchain as an auditable access control layer. Smart contracts are tailored for the IoTChain model, which combines the Ethereum blockchain and the interplanetary file system (IPFS). We used an advanced encryption standard (AES) for encryption and the elliptic curve Diffie-Hellman key exchange protocol for secret key sharing between data owners and users. Also, the proof-of-work (PoW) consensus mechanism is replaced with a proof-of-authority (PoA) to minimize system transaction cost and boost system throughput. Additionally, our solution has been tested on the Ethereum official test network Rinkeby, and the results demonstrate that our approach is realistic and economical on the IoT data.
Mohammad Madine, Khaled Salah, Raja Jayaraman, Ammar Battah · 6 authors
Digital data has enabled organizations to anticipate future threats, opportunities, and trends. However, digital data owners do not know how their data is accessed, shared, and monitized. In this paper, we propose using blockchain technology and non-fungible tokens (NFTs) to enable time-bound access and monitization of private data. Our approach allows users to upload encrypted content and mint it into NFTs. Other users can access the NFTsâ content by requesting a purchase or a license. Purchasing content transfers the ownership of the NFTs to the buyer; whereas, licensing them permits accessing the private data for a limited period of time, after which the data gets automatically deleted. Our developed approach uses the decentralized application (DApp), proxy reencryption (PRE), InterPlanetary File System (IPFS), and trusted execution environment (TEE) for managing a fully decentralized and robust system. We implement a proof-of-concept system in an Ethereum-based environment, which is used for testing and vulnerability checks. We present the cost and security analyses and discuss the generalization aspect of the solution. Our smart contracts and testing scripts are publicly available under an open-source license.
In recent years, Blockchain is gaining prominence as a hot topic in academic research. However, the consensus mechanism of blockchain has been criticized in terms of energy consumption and performance. Although Proof-of-Authority (PoA) consensus mechanism, as a lightweight consensus mechanism, is more efficient than traditional Proof-of-Work (PoW) and Proof-of-Stake (PoS), it suffers from the problem of centralization. To this end, on account of analyzing the shortcomings of existing consensus mechanisms, this paper proposes a dynamic reputation-based consensus mechanism for blockchain. This scheme allows nodes with reputation value higher than a threshold apply to become a monitoring node, which can monitor the behavior of validators in case that validators with excessive power cause harm to the blockchain network. At the same time, the reputation evaluation algorithm is also introduced to select nodes with high reputation to become validators in the network, thus increasing the cost of malicious behavior. In each consensus cycle, validators and monitoring nodes are dynamically updated according to the reputation value. Through security analysis, it is demonstrated that the scheme can resist the attacks of malicious nodes in the blockchain network. By simulation experiments and analysis of the scheme, the result verifies that the mechanism can effectively improve the fault tolerance of the consensus mechanism, reduce the time of consensus to guarantee the security of the system.
Since public blockchains are permissionless, it is subject to passive adversarial attack. In 5irechain we have addressed the security problem related to this passive adversarial activity by applying 5ireHE, a homomorphic encryption technique that encrypts the transactional details using the receiverâs public key. Since the transaction is encrypted by the receiverâs public key, it is harder for other validators to validate the transaction in 5ire. In this paper, we introduce ZKP for validating the transaction in a sense that validator can check if the senderâs previous balance and the remaining balance are in harmony with the amount of the transaction despite the difference in public keys that are used for the encryption of transaction and the encryption of account balance.
By supporting decentralized applications (DApps), modern blockchains have become the technology of choice for the Web3, a decentralized way for people to interact with each other. As the popularity of DApps is growing, the challenge is now to allocate shard or subnetwork resources to face the associated demand of individual DApps. Unfortunately, most sharding proposals are inherently static as they cannot be adjusted at runtime. Given that blockchains are expected to run for years without interruption, these proposals are insufficient to cope with the upcoming demand. In this paper, we present dynamic blockchain sharding, a new way to create and close shards on-demand, and adjust their size at runtime without requiring to hard fork (i.e., creating duplicated instances of the same blockchain). The novel idea is to reconfigure sharding through dedicated smart contract invocations: not only does it strengthen the security of the sharding reconfiguration, it also makes it inherently transparent as any other blockchain data. Similarly to classic sharding, our protocol relies on randomness to cope with shard-takeover attacks and on rotating nodes to cope with the bribery of a slowly-adaptive adversary. By contrast, however, our protocol is ideally suited for open networks as it does not require fully synchronous communications. To demonstrate its efficiency, we deploy it in 10 countries over 5 continents and demonstrate that its performance increases quasi-linearly with the number of shards as it reaches close to 14,000 TPS on only 8 shards.
Omar Sefraoui, Afaf Bouzidi, Kamal Ghoumid, El Miloud Ar-Reyouchi
Nowadays, connected devices are growing exponen-tially; their produced data traffic has increased unprecedent-edly. Information systems security and cybersecurity are critical because data typically contain sensitive personal information, requiring high data protection. An authentication system manages and controls access to this data allowing the system to ensure the legitimacy of the access request. Most of the current identification and authentication systems are based on a centralized architec-ture. However, some concepts as Cloud computing and Blockchain use respectively distributed and decentralized architectures. Users without a central server will own platforms and applications of the next generation of Internet and Web3. This paper proposes AuSDiDe, a new authentication system for the distributed and decentralized structure. This solution aims to divide and share keys toward different and distributed nodes. The main objective of AuSDiDe is to securely store and manage passwords, private keys, and authentication based on the Shamir secret sharing algo-rithm. This new proposal significantly reinforces data protection in information security.