Context: Smart contracts are computer programs that are automatically executed on the blockchain. Vulnerabilities in their implementation have led to severe loss of cryptocurrency. Smart contracts become immutable when deployed to the Ethereum blockchain. Therefore, it is essential to understand the nature of vulnerabilities in Ethereum smart contracts to prevent them in the future. Existing classifications exist, but are limited in several ways. Objective: We aim to characterize vulnerabilities in Ethereum smart contracts written in Solidity, and unify existing classifications schemes. Method: We extracted 2143 vulnerabilities from public coding platforms and popular vulnerability databases and categorized them using a card sorting approach. We targeted the Ethereum blockchain in this paper, as it is the first and most popular blockchain to support the deployment of smart contracts, and Solidity as the most widely used language to implement smart contracts. We devised a classification scheme of smart contract vulnerabilities according to their error source and impact. Afterwards, we mapped existing classification schemes to our classification. Results: The resulting classification consists of 11 categories describing the error source of a vulnerability and 13 categories describing potential impacts. Our findings show that the language specific coding and the structural data flow categories are the dominant categories, but that the frequency of occurrence differs substantially between the data sources. Conclusions: Our findings enable researchers to better understand smart contract vulnerabilities by defining various dimensions of the problem and supporting our classification with mappings with literature-based classifications and frequency distributions of the defined categories.
With the rapid development of cloud servers, storing data on cloud servers has become a popular option. However, cloud servers are centralized. Storing data on centralized cloud servers may involve some risks. For example, the data access pattern may be revealed when accessing data on cloud servers. Therefore, protecting a user’s patterns has become a crucial concern. Oblivious RAM (ORAM) is a candidate solution to hide the data access pattern. However, it inherently induces some overhead of accessing data, and many blockchain-based applications also do not consider the access pattern leakage issues. In this paper, we address these issues above by proposing a decentralized database system with oblivious access in a (parallel) smart contract model. The interactions of oblivious access are asymmetric where the smart contract side is expected to put much effort into computation. The proposed system slightly reduces the overhead of ORAM and overcomes the issues stemming from the centralization of servers. The main techniques are to use the garbled circuits to reduce the cost of communication and to combine with the parallel smart contract model to (conceptually) improve the performance of smart contract execution on the blockchain.
With the rapid development of blockchain, big data, cloud computing, and artificial intelligence, the security of multisource data collaborative computing has become increasingly prominent. Secure multiparty computing has become the core technology of privacy collaborative computing. Millionaires’ problem is the cornerstone of secure multiparty computation. Firstly, this paper proposes a 0-1 coding rule, which is used to solve the millionaires’ problem under the semihonest model. Aiming at the possible malicious behaviors of the protocol under the semihonest model, the millionaires’ problem protocol under the malicious model based on the elliptic curve cryptography is designed by using cryptographic tools such as the zero-knowledge proof and the cut-choose method. This protocol not only can effectively solve the millionaires’ problem but also can safely and effectively prevent malicious behaviors. Meanwhile, the security ordering designed by the protocol can be effectively applied to a quality evaluation in the blockchain.
Digital document communication between an enterprise and a customer is becoming a primary form of communication rather than the traditional physical document communication. A PDF document, the most popular document format, provides an identical document layout regardless of OS or device and has a content integrity verification feature with a digital signature. However, it has a bad user experience, such as low readability on a mobile device. On the other hand, an HTML document has a weakness in verifying the content integrity even though it is the primary document format and provides a good user experience on mobile devices. There are certified document services using blockchain technology, but it is still vulnerable to verifying content integrity. Furthermore, research on the document HTML has proposed the trusted document generation technique by HTML conformance and digital signature; however, this research does not provide content delivery verification, and there is a file size overhead. In this paper, we have developed the chained document HTML by defining HTML conformance, digital signature, and blockchain technology. First, the chained document HTML has to embed all resources and does not allow loading content on-demand. Second, the file is signed by a digital signature, and the signature value is added in the file header. Lastly, the metadata to verify the content integrity is inserted in a blockchain node. We have created the chained document HTML generation and verification experiment environment by Ethereum and Python. We have confirmed that the chained document HTML provides content and delivery integrity verification in the research. We expect the chained document HTML will be widely used in document communication between an enterprise and a customer, especially if the document has sensitive personal information that might have a legal dispute.
User transactions on Ethereum's peer-to-peer network are at risk of being attacked. The smart contracts building decentralized finance (DeFi) have introduced a new transaction ordering dependency to the Ethereum blockchain. As a result, attackers can profit from front- and back-running transactions. Multiple approaches to mitigate transaction reordering manipulations have surfaced recently. However, the success of individual approaches in mitigating such attacks and their impact on the entire blockchain remains largely unstudied. In this systematization of knowledge (SoK), we categorize and analyze state-of-the-art transaction reordering manipulation mitigation schemes. Instead of restricting our analysis to a scheme's success at preventing transaction reordering attacks, we evaluate its full impact on the blockchain. Therefore, we are able to provide a complete picture of the strengths and weaknesses of current mitigation schemes. We find that currently no scheme fully meets all the demands of the blockchain ecosystem. In fact, all approaches demonstrate unsatisfactory performance in at least one area relevant to the blockchain ecosystem.
Cryptocurrencies are poised to revolutionize the modern economy by democratizing commerce. These currencies operate on top of blockchain-based distributed ledgers. Existing permissionless blockchain-based protocols offer unparalleled benefits like decentralization, anonymity, and transparency. However, these protocols suffer in performance which hinders their widespread adoption. In particular, high time-to-finality and low transaction rates keep them from replacing centralized payment systems such as the Visa network. Permissioned blockchain protocols offer attractive performance guarantees, but they are not considered suitable for deploying decentralized cryptocurrencies due to their centralized nature. Researchers have developed several multi-layered blockchain protocols that combine both permissioned and permissionless blockchain protocols to achieve high performance along with decentralization. The key idea with existing layered blockchain protocols in literature is to divide blockchain operations into two layers and use different types of blockchain protocols to manage each layer. However, many such works come with the assumptions of honest majority which may not accurately reflect the real world where the participants may be self-interested or rational. These assumptions may render the protocols susceptible to security threats in the real world, as highlighted by the literature focused on exploring game-theoretic attacks on these protocols. We generalize the "layered" approach taken by existing protocols in the literature and present a framework to analyze the system in the BAR Model and provide a generalized game-theoretic analysis of such protocols. Using our analysis, we identify the critical system parameters required for a distributed ledger's secure operation in a more realistic setting.
Searchable symmetric encryption (SSE) provides an effective way to search encrypted data stored on untrusted servers. When the server is not trusted, it is indispensable to verify the results returned by it. However, the existing SSE schemes either lack fairness in the verification of search results, or do not support the verification of multiple keywords. To address this, we designed a multi-keyword verifiable searchable symmetric encryption scheme based on blockchain, which provides an efficient multi-keyword search and fair verification of search results. We utilized bitmap to build a search index in order to improve search efficiency, and used blockchain to ensure fair verification of search results. The bitmap and hash function are combined to realize lightweight multi-keyword search result verification, compared with the existing verification schemes using public key cryptography primitives, our scheme reduces the verification time and improves the verification efficiency. In addition, our scheme supports the dynamic update of files and realizes the forward security in update. Finally, formal security analysis proves that our scheme is secure against Chosen-Keyword Attacks (CKA), experimental analysis demonstrations that our scheme is efficient and viable in practice.
As increasing clients tend to outsource massive multimedia data generated by Internet of Things (IoT) devices to the cloud, data auditing is becoming crucial, as it enables clients to verify the integrity of their outsourcing data. However, most existing data auditing schemes cannot guarantee 100% data integrity and cannot meet the security requirement of practical multimedia services. Moreover, the lack of fair arbitration leads to clients not receiving compensation in a timely manner when the outsourced data is corrupted by the cloud service provider (CSP). In this work, we propose an arbitrable data auditing scheme based on the blockchain. In our scheme, clients usually only need to conduct private audits, and public auditing by a smart contract is triggered only when verification fails in private auditing. This hybrid auditing design enables clients to save audit fees and receive compensation automatically and in a timely manner when the outsourced data are corrupted by the CSP. In addition, by applying the deterministic checking technique based on a bilinear map accumulator, our scheme can guarantee 100% data integrity. Furthermore, our scheme can prevent fraudulent claims when clients apply for compensation from the CSP. We analyze the security strengths and complete the prototype’s implementation. The experimental results show that our blockchain-based data auditing scheme is secure, efficient, and practical.
In this study, we propose a blockchain-based privacy-preserving vaccine passport system for the global prevention and control of infectious diseases. The system operates a double-chain framework which consists of a public blockchain and a consortium blockchain. Among them, the combination of the immutability of the public blockchain and Internet of Things (IoT) technology in the supply chain ensures the openness and transparency of the cold chain logistics records of the vaccines covering the stages from auditing to the target vaccination hospitals. The system adopts the consortium blockchain to achieve the balance between the protection of users’ vaccination privacy and auditing by the government departments. Specifically, a distributed system-based threshold signature is adopted in the vaccine qualification phase to resist collusion between the vaccine manufacturing company and vaccine approval institutions. The cryptographic tools such as the anonymous credentials, zero-knowledge protocols, and range proofs ensure that users do not disclose any private information other than proving that they have a legally valid vaccine passport when users display the vaccine passports to customs. At the same time, customs can apply various vaccine prevention policies based on the conditions on the specific vaccine passports. Regarding the security properties of the system, a formal security model is given along with the corresponding security proofs.
The blockchain-based smart contract lacks privacy since the contract state and instruction code are exposed to the public. Combining smart-contract execution with Trusted Execution Environments (TEEs) provides an efficient solution, called TEE-assisted smart contracts, for protecting the confidentiality of contract states. However, the combination approaches are varied, and a systematic study is absent. Newly released systems may fail to draw upon the experience learned from existing protocols, such as repeating known design mistakes or applying TEE technology in insecure ways. In this paper, we first investigate and categorize the existing systems into two types: the layer-one solution and layer-two solution. Then, we establish an analysis framework to capture their common lights, covering the desired properties (for contract services), threat models, and security considerations (for underlying systems). Based on our taxonomy, we identify their ideal functionalities and uncover the fundamental flaws and reasons for the challenges in each specification design. We believe that this work would provide a guide for the development of TEE-assisted smart contracts, as well as a framework to evaluate future TEE-assisted confidential contract systems.
Since FinTech was stimulated by the invention of blockchain, without the full realization of blockchain technologies in the following years, FinTech has not been fully realized. We discuss some myths and reasons for why blockchain technologies were not fully realized. The lack of distributed synchronization might be the most difficult challenge such that the trust provided by blockchain is not good enough for public use. We propose a mathematical solution with a new consensus mechanism based on general Proof-of-Work mining, called Proof-of-PowerTimestamp, to reach distributed synchronization and reduce power consumption to less than one billionth of Bitcoin. We also discuss related issues toward blockchain realization once the distributed synchronization and energy consumption problems are solved. Since the issues are mostly interdisciplinary or multidisciplinary, researchers are invited to cooperate to help blockchain realization as soon as possible.
Data security plays a major role in computer network. Because it helps to transmit data in secure way over the Internet. So we need to use strong security method for secure data transaction. Cryptography is a security tool which helps to transmit information from one place to another place over computer network. Cryptography follows encryption and decryption methods for data transmission. Cryptographic technique is completely based on key generation because it needs keys to transmit data between users. However cryptography works well in secure data transmission but it needs keys to provide security for data. In cryptography generation of keys taking more time than transmission of data. So in this paper we discuss about Zero-Knowledge Proof (ZKP) which is also based on cryptographic technique. ZKP is also useful in secure data transmission without sharing key values between users. This paper tells about overview of ZKP and how it is useful in data transmission.
Internet-of-Things (IoT) are increasingly operating in the zero-trust environments where any devices and systems may be compromised and hence untrusted. In addition, data collected by and sent from IoT devices may be shared with and processed by edge computing systems, in order to reduce the reliance on centralized (cloud) servers, leading to further security and privacy issues. To cope with these challenges, this paper proposes an innovative blockchain-enabled information sharing solution in zero-trust context to guarantee anonymity yet entity authentication, data privacy yet data trustworthiness, and participant stimulation yet fairness. This new solution is able to support filtering of fabricated information through smart contracts, effective voting, and consensus mechanisms, which can prevent unauthenticated participants from sharing garbage information. We also prove that the proposed solution is secure in the universal composability framework, and further evaluate its performance over an Ethereum-based blockchain platform to demonstrate its utility.
Electronic Health Records (EHRs) are essential in contemporary healthcare as they facilitate the storage and sharing of personal patient data. Traditional cloud-based EHR systems, though, are afflicted with centralized control, privacy threats, restricted interoperability, and susceptibility to data breaches. To alleviate these challenges, this paper suggests a blockchain-based, patient-centered EHR management system that uses Ethereum smart contracts, Decentralized Identifiers (DIDs), and InterPlanetary File System (IPFS) for safe, distributed, and effective handling of health data.The system put forward puts patients at the forefront of EHR access and control, allowing them to grant or withdraw permissions to healthcare providers, insurers, or researchers using fine-grained, attribute-based policies executed through smart contracts. DIDs remove the need for third-party identity providers, providing secure and verifiable user authentication directly on the blockchain. IPFS, on the other hand, provides cost-effective, tamper-proof off-chain storage of medical records, with metadata and access logs stored on-chain to minimize gas usage.Extensive testing on the Ethereum Goerli testnet proves that the system provides greater security, lower storage costs, efficient access control, and better interoperability than conventional models. This method not only solves existing shortcomings in EHR systems but also opens the door to scalable, transparent, and patient-enabled healthcare data management.
The Open Vote Network is a self-tallying decentralized e-voting protocol suitable for boardroom elections. Currently, it has two Ethereum-based implementations: the first, by McCorry et al., has a scalability issue since all the computations are performed on-chain. The second implementation, by Seifelnasr et al., solves this issue partially by assigning a part of the heavy computations to an off-chain untrusted administrator in a verifiable manner. As a side effect, this second implementation became not dispute-free; there is a need for a tally dispute phase where an observer interrupts the protocol when the administrator cheats, i.e., announces a wrong tally result. In this work, we propose a new smart contract design to tackle the problems in the previous implementations by (i) preforming all the heavy computations off-chain hence achieving higher scalability, and (ii) utilizing zero-knowledge Succinct Non-interactive Argument of Knowledge (zk-SNARK) to verify the correctness of the off-chain computations, hence maintaining the dispute-free property. To demonstrate the effectiveness of our design, we develop prototype implementations on Ethereum and conduct multiple experiments for different implementation options that show a trade-off between the zk-SNARK proof generation time and the smart contract gas cost, including an implementation in which the smart contract consumes a constant amount of gas independent of the number of voters.
Proof of Authority (PoA) is a type of permissioned consensus algorithm with a fixed committee. PoA has been widely adopted by communities and industries due to its better performance and faster finality. In this paper, we explore the \textit{unfairness} issue existing in the current PoA implementations. We have investigated 2,500+ \textit{in the wild} projects and selected 10+ as our main focus (covering Ethereum, Binance smart chain, etc.). We have identified two types of order manipulation attacks to separately break the transaction-level (a.k.a. transaction ordering) and the block-level (sealer position ordering) fairness. Both of them merely rely on honest-but-\textit{profitable} sealer assumption without modifying original settings. We launch these attacks on the forked branches under an isolated environment and carefully evaluate the attacking scope towards different implementations. To date (as of Nov 2021), the potentially affected PoA market cap can reach up to $681,087$ million USD. Besides, we further dive into the source code of selected projects, and accordingly, propose our recommendation for the fix. To the best of knowledge, this work provides the first exploration of the \textit{unfairness} issue in PoA algorithms.
Aarushi Goel, Matthew Green, Mathias Hall-Andersen, Gabriel Kaptchuk
Abstract Set membership proofs are an invaluable part of privacy preserving systems. These proofs allow a prover to demonstrate knowledge of a witness w corresponding to a secret element x of a public set, such that they jointly satisfy a given NP relation, i.e. ℛ( w, x ) = 1 and x is a member of a public set { x 1 , . . . , x 𝓁 }. This allows the identity of the prover to remain hidden, eg. ring signatures and confidential transactions in cryptocurrencies. In this work, we develop a new technique for efficiently adding logarithmic-sized set membership proofs to any MPC-in-the-head based zero-knowledge protocol (Ishai et al. [STOC’07]). We integrate our technique into an open source implementation of the state-of-the-art, post quantum secure zero-knowledge protocol of Katz et al. [CCS’18].We find that using our techniques to construct ring signatures results in signatures (based only on symmetric key primitives) that are between 5 and 10 times smaller than state-of-the-art techniques based on the same assumptions. We also show that our techniques can be used to efficiently construct post-quantum secure RingCT from only symmetric key primitives.
Abstract Traditional zero-knowledge protocols have been studied and optimized for the setting where a single prover holds the complete witness and tries to convince a verifier about a predicate on the witness, without revealing any additional information to the verifier. In this work, we study the notion of distributed-prover zero knowledge (DPZK) for arbitrary predicates where the witness is shared among multiple mutually distrusting provers and they want to convince a verifier that their shares together satisfy the predicate. We make the following contributions to the notion of distributed proof generation: (i) we propose a new MPC-style security definition to capture the adversarial settings possible for different collusion models between the provers and the verifier, (ii) we discuss new efficiency parameters for distributed proof generation such as the number of rounds of interaction and the amount of communication among the provers, and (iii) we propose a compiler that realizes distributed proof generation from the zero-knowledge protocols in the Interactive Oracle Proofs (IOP) paradigm. Our compiler can be used to obtain DPZK from arbitrary IOP protocols, but the concrete efficiency overheads are substantial in general. To this end, we contribute (iv) a new zero-knowledge IOP Graphene which can be compiled into an efficient DPZK protocol. The (D + 1)-DPZK protocol D-Graphene, with D provers and one verifier, admits O ( N 1 /c ) proof size with a communication complexity of O (D 2 ·( N 1−2 /c + N s )), where N is the number of gates in the arithmetic circuit representing the predicate and N s is the number of wires that depends on inputs from two or more parties. Significantly, only the distributed proof generation in D-Graphene requires interaction among the provers. D-Graphene compares favourably with the DPZK protocols obtained from the state-of-art zero-knowledge protocols, even those not modelled as IOPs.
Sana Amjad, Shahid Abbas, Zain Abubaker, Mohammed H. Alsharif · 6 authors
This paper proposes a blockchain-based node authentication model for the Internet of sensor things (IoST). The nodes in the network are authenticated based on their credentials to make the network free from malicious nodes. In IoST, sensor nodes gather the information from the environment and send it to the cluster heads (CHs) for additional processing. CHs aggregate the sensed information. Therefore, their energy rapidly depletes due to extra workload. To solve this issue, we proposed distance, degree, and residual energy-based low-energy adaptive clustering hierarchy (DDR-LEACH) protocol. DDR-LEACH is used to replace CHs with the ordinary nodes based on maximum residual energy, degree, and minimum distance from BS. Furthermore, storing a huge amount of data in the blockchain is very costly. To tackle this issue, an external data storage, named as interplanetary file system (IPFS), is used. Furthermore, for ensuring data security in IPFS, AES 128-bit is used, which performs better than the existing encryption schemes. Moreover, a huge computational cost is required using a proof of work consensus mechanism to validate transactions. To solve this issue, proof of authority (PoA) consensus mechanism is used in the proposed model. The simulation results are carried out, which show the efficiency and effectiveness of the proposed system model. The DDR-LEACH is compared with LEACH and the simulation results show that DDR-LEACH outperforms LEACH in terms of energy consumption, throughput, and improvement in network lifetime with CH selection mechanism. Moreover, transaction cost is computed, which is reduced by PoA during data storage on IPFS and service provisioning. Furthermore, the time is calculated in the comparison of AES 128-bit scheme with existing scheme. The formal security analysis is performed to check the effectiveness of smart contract against attacks. Additionally, two different attacks, MITM and Sybil, are induced in our system to show our system model's resilience against cyber attacks.
We present two attacks targeting the Proof-of-Stake (PoS) Ethereum consensus protocol. The first attack suggests a fundamental conceptual incompatibility between PoS and the Greedy Heaviest-Observed Sub-Tree (GHOST) fork choice paradigm employed by PoS Ethereum. In a nutshell, PoS allows an adversary with a vanishing amount of stake to produce an unlimited number of equivocating blocks. While most equivocating blocks will be orphaned, such orphaned `uncle blocks' still influence fork choice under the GHOST paradigm, bestowing upon the adversary devastating control over the canonical chain. While the Latest Message Driven (LMD) aspect of current PoS Ethereum prevents a straightforward application of this attack, our second attack shows how LMD specifically can be exploited to obtain a new variant of the balancing attack that overcomes a recent protocol addition that was intended to mitigate balancing-type attacks. Thus, in its current form, PoS Ethereum without and with LMD is vulnerable to our first and second attack, respectively.
As a recent decentralized business model, Distributed Autonomous Organization (DAO) challenges the management paradigms of conventional organizations and represents the future of democracy-based systems. However, DAOs are facing challenges that can be divided into two categories, including policy-based and technical challenges. Detecting misbehaving nodes is a crucial challenge that is considered in both categories. Designing mechanisms to report malicious behaviors while maintaining anonymity is essential for the survival and efficiency of DAOs. In this paper, we clarify the problem, and introduce Blockchain-Based Anonymous Reporting (BBAR) as a collective monitoring mechanism in DAOs with its requirements and implementation methods.
Adam Ibrahim Abdi, Fathy Eassa, Kamal Jambi, Khalid Ali Almarhabi · 7 authors
The rapid growth of the Internet of Things (IoT) and its attributes of constrained devices and a distributed environment make it difficult to manage such a huge and growing network of devices on a global scale. Existing traditional access-control systems provide security and management to the IoT system. However, these mechanisms are based on central authority management, which introduces issues such as a single point of failure, low scalability, and a lack of privacy. In order to address these problems, many researchers have proposed using blockchain technology to achieve decentralized access control. However, such models are still faced with problems such as a lack of scalability and high computational complexity. In this paper, we propose a light-weight hierarchical blockchain-based multi-chaincode access control to protect the security and privacy of IoT systems. A clustering concept with BC managers enables the extended scalability of the proposed system. The architecture of the proposed solution contains three main components: an Edge Blockchain Manager (EBCM), which is responsible for authenticating and authorizing constrained devices locally; an Aggregated Edge Blockchain Manager (AEBCM), which contains various EBCMs to control different clusters and manage ABAC policies, and a Cloud Consortium Blockchain Manager (CCBCM), which ensures that only authorized users access the resources. In our solution, smart contracts are used to self-enforce decentralized AC policies. We implement a proof of concept for our proposed system using the permissioned Hyperledger Fabric. The simulation results and the security analysis show the efficiency and effectiveness of the proposed solution.
Cong Deng, Lin You, Xianghong Tang, Gengran Hu · 5 authors
Zero-Knowledge Proof is widely used in blockchains. For example, zk-SNARK is used in Zcash as its core technology to identifying transactions without the exposure of the actual transaction values. Up to now, various range proofs have been proposed, and their efficiency and range-flexibility have also been improved. Bootle et al. used the inner product method and recursion to construct an efficient Zero-Knowledge Proof in 2016. Later, Benediky Bünz et al. proposed an efficient range proof scheme called Bulletproofs, which can convince the verifier that a secret number lies in [0,2κ−1] with κ being a positive integer. By combining the inner-product and Lagrange’s four-square theorem, we propose a range proof scheme called Cuproof. Our Cuproof can make a range proof to show that a secret number v lies in an interval [a,b] with no exposure of the real value v or other extra information leakage about v. It is a good and practical method to protect privacy and information security. In Bulletproofs, the communication cost is 6+2logκ, while in our Cuproof, all the communication cost, the proving time and the verification time are of constant sizes.