Daniel Conte de Leon, Antonius Q. Stalick, Ananth A. Jillepalli, Michael Haney · 5 authors
Purpose - The purpose of this article is to clarify current and widespread misconceptions about the properties of blockchain technologies and to describe challenges and avenues for correct and trustworthy design and implementation of distributed ledger system (DLS) or Technology (DLT). Design/methodology/approach - The authors contrast the properties of a blockchain with desired, however emergent, properties of a DLS, which is a complex and distributed system. They point out and justify, with facts and analysis, current misconceptions about the blockchain and DLSs. They describe challenges that these systems will need to address and possible solution avenues for achieving trustworthiness. Findings - Many of the statements that have appeared on the internet, news and academic articles, such as immutable ledger and exact copies, may be misleading. These are desired emergent properties of a complex system, not assured properties. It is well-known within the distributed systems and critical software community that it is extremely hard to prove that a complex system correctly and completely implements emergent properties. Further research and development for trustworthy DLS design and implementation is needed, both practical and theoretical. Research limitations/implications - This is the first known published attempt at describing current misconceptions about blockchain technologies. Further collaborative work, discussions, potential solutions, evaluations, resulting publications and verified reference implementations are needed to ensure DLTs are safe, secure, and trustworthy. Practical implications - Interdisciplinary teams with members from academia, business and industry, and from disciplines such as business, entrepreneurship, theoretical and practical computer science, cybersecurity, finance, mathematics and statistics, must be formed. Such teams must collaborate with the objective of developing strategies and techniques for ensuring the correctness and security of future DLSs in which our society may become dependent. Originality value - The value and originality of this article is twofold: the disproving, through fact collection and systematic analysis, of current misconceptions about the properties of the blockchain and DLSs, and the discussion of challenges to achieving adequate trustworthiness along with the proposal of general avenues for possible solutions.
Blockchain is one of the hottest topics in the discussion of technologies lately. As the enabling technology for Bitcoin, the pioneering cryptocurrency, blockchain is an append-only distributed ledger that is virtually impossible to attack given sufficient scale of participants. Hence, blockchain holds great promises as the fundamental technology to enable Internet-based electronic voting. However, Internet-based voting has additional requirements than monetary transactions. In this paper, we analyze these requirements, review existing proposed solutions, and outline possible improvements. Specifically, we propose to use live biometrics of the voter to perform secure and highly reliable remote authentication. We also propose a scheme to protect the secrecy of the ballots and eliminate the influence of votes already cast. Finally, we propose to impose a hierarchy to the voting infrastructure that aligns naturally with traditional voting, which enables parallel processing of multiple blockchains, to overcome the intrinsic scalability limitation of the blockchain technology.
The Internet of Things (IoT) has penetrated deeply into our lives and the number of IoT devices per person is expected to increase substantially over the next few years. Due to the characteristics of IoT devices (i.e., low power and low battery), usage of these devices in critical applications requires sophisticated security measures. Researchers from academia and industry now increasingly exploit the concept of blockchains to achieve security in IoT applications. The basic idea of the blockchain is that the data generated by users or devices in the past are verified for correctness and cannot be tampered once it is updated on the blockchain. Even though the blockchain supports integrity and non-repudiation to some extent, confidentiality and privacy of the data or the devices are not preserved. The content of the data can be seen by anyone in the network for verification and mining purposes. In order to address these privacy issues, we propose a new privacy-preserving blockchain architecture for IoT applications based on attribute-based encryption (ABE) techniques. Security, privacy, and numerical analyses are presented to validate the proposed model.
Preuves à divulgation nulle de connaissance pour le calcul sécurisé Dans cette thèse, nous étudions les preuves à divulgation nulle de connaissance, une primitive cryptographique permettant de prouver une assertion en ne révélant rien de plus que sa véracité, et leurs applications au calcul sécurisé. Nous introduisons tout d’abord un nouveau type de preuves à divulgation nulle, appelées arguments implicites à divulgation nulle, intermédiaire entre deux notions existantes, les preuves interactives et les preuves non interactives à divulgation nulle. Cette nouvelle notion permet d’obtenir les mêmes bénéfices en terme d’efficacité que les preuves non-interactives dans le contexte de la construction de protocoles de calcul sécurisé faiblement interactifs, mais peut être instanciée à partir des mêmes hypothèses cryptographiques que les preuves interactives, permettant d’obtenir de meilleures garanties d’efficacité et de sécurité. Dans un second temps, nous revisitons un système de preuves à divulgation nulle de connaissance qui est particulièrement utile dans le cadre de protocoles de calcul sécurisé manipulant des nombres entiers, et nous démontrons que son analyse de sécurité classique peut être améliorée pour faire reposer ce système de preuve sur une hypothèse plus standard et mieux connue. Enfin, nous introduisons une nouvelle méthode de construction de systèmes de preuves à divulgation nulle sur les entiers, qui représente une amélioration par rapport aux méthodes existantes, tout particulièrement dans un modèle de type client-serveur, où un client à faible puissance de calcul participe à un protocole de calcul sécurisé avec un serveur à forte puissance de calcul.
The adoption of blockchain-based distributed computation platforms is growing fast. Some of these platforms, such as Ethereum, provide support for implementing smart contracts, which are envisioned to have novel applications in a broad range of areas, including finance and Internet-of-Things. However, a significant number of smart contracts deployed in practice suffer from security vulnerabilities, which enable malicious users to steal assets from a contract or to cause damage. Vulnerabilities present a serious issue since contracts may handle financial assets of considerable value, and contract bugs are non-fixable by design. To help developers create more secure smart contracts, we introduce FSolidM, a framework rooted in rigorous semantics for designing con- tracts as Finite State Machines (FSM). We present a tool for creating FSM on an easy-to-use graphical interface and for automatically generating Ethereum contracts. Further, we introduce a set of design patterns, which we implement as plugins that developers can easily add to their contracts to enhance security and functionality.
The adoption of blockchain-based distributed computation platforms is growing\nfast. Some of these platforms, such as Ethereum, provide support for\nimplementing smart contracts, which are envisioned to have novel applications\nin a broad range of areas, including finance and Internet-of-Things. However, a\nsignificant number of smart contracts deployed in practice suffer from security\nvulnerabilities, which enable malicious users to steal assets from a contract\nor to cause damage. Vulnerabilities present a serious issue since contracts may\nhandle financial assets of considerable value, and contract bugs are\nnon-fixable by design. To help developers create more secure smart contracts,\nwe introduce FSolidM, a framework rooted in rigorous semantics for designing\ncon- tracts as Finite State Machines (FSM). We present a tool for creating FSM\non an easy-to-use graphical interface and for automatically generating Ethereum\ncontracts. Further, we introduce a set of design patterns, which we implement\nas plugins that developers can easily add to their contracts to enhance\nsecurity and functionality.\n
In this paper, we propose a zero-knowledge proof for a special case of the hidden subset sum problem. This problem was presented by [Boyko et al. 1998] as the underlying problem of methods for generating random pairs of the form (x, gx (mod p)) using precomputations. The proof we propose is an adaptation of a zero-knowledge protocol for the subset sum problem presented by [Blocki 2009].
At present, the cloud storage used in searchable symmetric encryption schemes (SSE) is provided in a private way, which cannot be seen as a true cloud. Moreover, the cloud server is thought to be credible, because it always returns the search result to the user, even they are not correct. In order to really resist this malicious adversary and accelerate the usage of the data, it is necessary to store the data on a public chain, which can be seen as a decentralized system. As the increasing amount of the data, the search problem becomes more and more intractable, because there does not exist any effective solution at present. In this paper, we begin by pointing out the importance of storing the data in a public chain. We then innovatively construct a model of SSE using blockchain(SSE-using-BC) and give its security definition to ensure the privacy of the data and improve the search efficiency. According to the size of data, we consider two different cases and propose two corresponding schemes. Lastly, the security and performance analyses show that our scheme is feasible and secure.
Muhammad Reza Rizky Fauzi, Surya Michrandi Nasution, Marisa W. Paryasto
The present study discusses the workings of blockchain bitcoin in the transactions sector, on the development of today's emerging computers in the financial sector of blockchain bitcoin traction. In this case the author analyzes how the transaction is running, as well as how blockchain bitcoin is doing work in transactions on the system to make transactions. Transaction is a data structure that encodes the transfer of values between users with in a bitcoin system. Every transaction is a public entry in this bitcoin blockchain. And become a large transaction bookkeeping global.
Decentralized digital currency systems known as cryptocurrencies are a breakthrough in electronic payments: the absence of a central authority can avoid the risk that a not fully reliable government seizes assets or causes hyperinflation, very small transactions can be made without incurring high costs and transactions can be traced, thus providing a tool to counter laundering and tax evasion. Furthermore, decentralization provides robustness against many attacks. Despite these advantages, cryptocurrencies have still not become mainstream solutions, because of scarce users’ inclination to adopt them as a privileged payment tool. This is mostly due to the absence of a structured form of control, which also prevents from having some credit insurance. Moreover, some present and future attacks, like quantum computer-based attacks, may threaten their security. In this paper we define new technical solutions to allow cryptocurrencies to become trusted tools for secure and verifiable digital transactions, and also for deposits, while preserving decentralization and users’ privacy. Based on a thorough security analysis, a new cryptocurrency model is first defined, exploiting a set of secure and post-quantum cryptographic primitives. Then, a secure supervision and authentication network is designed, which allows to control transactions, while guaranteeing users’ privacy. A robust reputation system for this context is also proposed, which helps to increase users’ trust and to reduce misconduct.
Divesh Aggarwal, Gavin K. Brennen, Troy Lee, Miklós Sántha · 5 authors
The key cryptographic protocols used to secure the internet and financial transactions of today are all susceptible to attack by the development of a sufficiently large quantum computer. One particular area at risk is cryptocurrencies, a market currently worth over 100 billion USD. We investigate the risk posed to Bitcoin, and other cryptocurrencies, by attacks using quantum computers. We find that the proof-of-work used by Bitcoin is relatively resistant to substantial speedup by quantum computers in the next 10 years, mainly because specialized ASIC miners are extremely fast compared to the estimated clock speed of near-term quantum computers. On the other hand, the elliptic curve signature scheme used by Bitcoin is much more at risk, and could be completely broken by a quantum computer as early as 2027, by the most optimistic estimates. We analyze an alternative proof-of-work called Momentum, based on finding collisions in a hash function, that is even more resistant to speedup by a quantum computer. We also review the available post-quantum signature schemes to see which one would best meet the security and efficiency requirements of blockchain applications.
Summary In a data sharing group, each user can upload, modify, and access group files and a user is required to generate a new signature for the modified file after modification. There is a situation that two or more users modify the same file at almost the same time, which should be avoided as it gives rise to a signature conflict. However, the existing schemes do not take it into consideration. In this paper, we proposed a new mechanism SeShare for data storing based on blockchain to realize signature uniqueness, which solves the problem of generating signatures for the same file meanwhile by different group users. Specifically, we record every signature of a file in a blockchain in chronological order, and only one user is allowed to add new signature at the end of the blockchain when modification conflicts occur. On the other hand, to provide a secure data sharing service, SeShare introduces an efficient public auditing scheme for file integrity verification when a group user leaves the group. We also prove the security of the proposed scheme and evaluate the performance at the end of this paper. Our experimental results demonstrate the efficiency of public auditing for user leaving.
Permissionless blockchains protocols such as Bitcoin are inherently limited in transaction throughput and latency. Current efforts to address this key issue focus on off-chain payment channels that can be combined in a Payment-Channel Network (PCN) to enable an unlimited number of payments without requiring to access the blockchain other than to register the initial and final capacity of each channel. While this approach paves the way for low latency and high throughput of payments, its deployment in practice raises several privacy concerns as well as technical challenges related to the inherently concurrent nature of payments that have not been sufficiently studied so far. In this work, we lay the foundations for privacy and concurrency in PCNs, presenting a formal definition in the Universal Composability framework as well as practical and provably secure solutions. In particular, we present Fulgor and Rayo. Fulgor is the first payment protocol for PCNs that provides provable privacy guarantees for PCNs and is fully compatible with the Bitcoin scripting system. However, Fulgor is a blocking protocol and therefore prone to deadlocks of concurrent payments as in currently available PCNs. Instead, Rayo is the first protocol for PCNs that enforces non-blocking progress (i.e., at least one of the concurrent payments terminates). We show through a new impossibility result that non-blocking progress necessarily comes at the cost of weaker privacy. At the core of Fulgor and Rayo is Multi-Hop HTLC, a new smart contract, compatible with the Bitcoin scripting system, that provides conditional payments while reducing running time and communication overhead with respect to previous approaches. Our performance evaluation of Fulgor and Rayo shows that a payment with 10 intermediate users takes as few as 5 seconds, thereby demonstrating their feasibility to be deployed in practice.
Ethan Cecchetti, Fan Zhang, Yan Ji, Ahmed E. Kosba · 6 authors
Blockchains and more general distributed ledgers are becoming increasingly popular as efficient, reliable, and persistent records of data and transactions. Unfortunately, they ensure reliability and correctness by making all data public, raising confidentiality concerns that eliminate many potential uses.
In this letter we propose Meta-key, a data-sharing mechanism that enables users share their encrypted data under a blockchain-based decentralized storage architecture. All the data-encryption keys are encrypted by the owner's public key and put onto the blockchain for safe and secure storage and easy key-management. Encrypted data are stored in dedicated storage nodes and proxy re-encryption mechanism is used to ensure secure data-sharing in the untrusted environment. Security analysis of our model shows that the proxy re-encryption adopted in our system is naturally free from collusion-attack due to the specific architecture of Meta-key.
Daniel Augot, Hervé Chabanne, Olivier Clémot, William R. George
The most fundamental purpose of blockchain technology is to enable\npersistent, consistent, distributed storage of information. Increasingly common\nare authentication systems that leverage this property to allow users to carry\ntheir personal data on a device while a hash of this data is signed by a\ntrusted authority and then put on a blockchain to be compared against. For\ninstance, in 2015, MIT introduced a schema for the publication of their\nacademic certificates based on this principle. In this work, we propose a way\nfor users to obtain assured identities based on face-to-face proofing that can\nthen be validated against a record on a blockchain. Moreover, in order to\nprovide anonymity, instead of storing a hash, we make use of a scheme of Brands\nto store a commitment against which one can perform zero-knowledge proofs of\nidentity. We also enforce the confidentiality of the underlying data by letting\nusers control a secret of their own. We show how our schema can be implemented\non Bitcoin's blockchain and how to save bandwidth by grouping commitments using\nMerkle trees to minimize the number of Bitcoin transactions that need to be\nsent. Finally, we describe a system in which users can gain access to services\nthanks to the identity records of our proposal.\n
David Froelicher, Patricia Egger, João Sá Sousa, Jean Louis Raisaro · 8 authors
Abstract Current solutions for privacy-preserving data sharing among multiple parties either depend on a centralized authority that must be trusted and provides only weakest-link security (e.g., the entity that manages private/secret cryptographic keys), or leverage on decentralized but impractical approaches (e.g., secure multi-party computation). When the data to be shared are of a sensitive nature and the number of data providers is high, these solutions are not appropriate. Therefore, we present U n L ynx , a new decentralized system for efficient privacy-preserving data sharing. We consider m servers that constitute a collective authority whose goal is to verifiably compute on data sent from n data providers. U n L ynx guarantees the confidentiality, unlinkability between data providers and their data, privacy of the end result and the correctness of computations by the servers. Furthermore, to support differentially private queries, U n L ynx can collectively add noise under encryption. All of this is achieved through a combination of a set of new distributed and secure protocols that are based on homomorphic cryptography, verifiable shuffling and zero-knowledge proofs. U n L ynx is highly parallelizable and modular by design as it enables multiple security/privacy vs. runtime tradeoffs. Our evaluation shows that U n L ynx can execute a secure survey on 400,000 personal data records containing 5 encrypted attributes, distributed over 20 independent databases, for a total of 2,000,000 ciphertexts, in 24 minutes.
Blockchain technology has evolved from being an immutable ledger of\ntransactions for cryptocurrencies to a programmable interactive the environment\nfor building distributed reliable applications. Although, blockchain technology\nhas been used to address various challenges, to our knowledge none of the\nprevious work focused on using blockchain to develop a secure and immutable\nscientific data provenance management framework that automatically verifies the\nprovenance records. In this work, we leverage blockchain as a platform to\nfacilitate trustworthy data provenance collection, verification, and\nmanagement. The developed system utilizes smart contracts and open provenance\nmodel (OPM) to record immutable data trails. We show that our proposed\nframework can efficiently and securely capture and validate provenance data,\nand prevent any malicious modification to the captured data as long as the\nmajority of the participants are honest.\n
Secret sharing is an important component of cryptography protocols and has a wide range of practical applications. However, the existing secret sharing schemes cannot apply to computationally weak devices and cannot efficiently guarantee fairness. In this study, a novel outsourcing secret sharing scheme is proposed. In the setting of outsourcing secret sharing, clients only need a small amount of decryption and verification operations, while the expensive reconstruction computation and verifiable computation can be outsourced to cloud service providers (CSP). The scheme does not require complex interactive argument or zero‐knowledge proof. The malicious behaviour of clients and CSP can be detected in time. Moreover, the CSP cannot get any useful information about the secret, and it is fair for every client to obtain the secret. At the end of this study, the authors prove the security of the proposed scheme and compare it with other secret sharing schemes.
A blockchain is a public ledger for recording transactions, maintained by<br> many nodes without central authority through a distributed cryptographic<br> protocol. All nodes validate the information to be appended to the<br> blockchain, and a consensus protocol ensures that the nodes agree on a<br> unique order in which entries are appended. Consensus protocols for<br> tolerating Byzantine faults have received renewed attention because they<br> also address blockchain systems. However, amid the current hype around<br> blockchains, cryptocurrencies, fintech startups, and novel consensus<br> mechanisms, it is sometimes overlooked that assessing and gaining<br> confidence in the resilience of a protocol is a difficult task. We argue that developing consensus protocols is similar to engineering<br> cryptographic systems, and that blockchain developers should look towards<br> the established experience in cryptography and security with building<br> trustworthy systems. Otherwise, it might be dangerous to entrust<br> financial value to new protocols. Public discussion, expert reviews,<br> broad validation, and standards recommendations should be employed,<br> following the established practice in cryptography and security.<br>
After more than eight years since the launch of Bitcoin, the decentralized transaction ledger functionality implemented through the blockchain technology is being used not only for cryptocurrencies, but to register, confirm and transfer any kind of contract and property. In this work, we analyze the most relevant functionalities and known issues of this technology, with the intent of pointing out the possible behaviours that are not as efficient and reliable as they should be when thinking with a broader outlook.
Open access
Blockchain Technology Applications and Security
Cryptography and Data Security
Advanced Steganography and Watermarking Techniques
Carlos Oliver, Alessandro Ricottone, Pericles Philippopoulos
We propose a proof-of-work algorithm that rewards blockchain miners for using computational resources to solve NP-complete puzzles. The resulting blockchain will publicly store and improve solutions to problems with real world applications while maintaining a secure and fully functional transaction ledger.
Paulo Matias, Pedro Barbosa, Thiago N.C. Cardoso, Diego M. Campos · 5 authors
Capture-the-flag (CTF) competitions are increasingly important for the Brazilian cybersecurity community as educational and professional tools. Unfortunately, CTF platforms may suffer from security issues, giving an unfair advantage to competitors. To mitigate this, we propose NIZKCTF, the first open-audit CTF platform based on noninteractive zero-knowledge proofs.
Tien Tuan Anh Dinh, Rui Liu, Meihui Zhang, Gang Chen · 6 authors
Blockchain technologies are gaining massive momentum in the last few years. Blockchains are distributed ledgers that enable parties who do not fully trust each other to maintain a set of global states. The parties agree on the existence, values, and histories of the states. As the technology landscape is expanding rapidly, it is both important and challenging to have a firm grasp of what the core technologies have to offer, especially with respect to their data processing capabilities. In this paper, we first survey the state of the art, focusing on private blockchains (in which parties are authenticated). We analyze both in-production and research systems in four dimensions: distributed ledger, cryptography, consensus protocol, and smart contract. We then present BLOCKBENCH, a benchmarking framework for understanding performance of private blockchains against data processing workloads. We conduct a comprehensive evaluation of three major blockchain systems based on BLOCKBENCH, namely Ethereum, Parity, and Hyperledger Fabric. The results demonstrate several trade-offs in the design space, as well as big performance gaps between blockchain and database systems. Drawing from design principles of database systems, we discuss several research directions for bringing blockchain performance closer to the realm of databases.