Follow blockchain research across journals, conferences, and preprint repositories.
2,350 results · page 92 of 98
Kevin Liao, Jonathan Katz
No abstract is available for this record.
Christian Cachin, Marko Vukolić
A blockchain is a distributed ledger for recording transactions, maintained by many nodes without central authority through a distributed cryptographic protocol. All nodes validate the information to be appended to the blockchain, and a consensus protocol ensures that the nodes agree on a unique order in which entries are appended. Consensus protocols for tolerating Byzantine faults have received renewed attention because they also address blockchain systems. This work discusses the process of assessing and gaining confidence in the resilience of a consensus protocols exposed to faults and adversarial nodes. We advocate to follow the established practice in cryptography and computer security, relying on public reviews, detailed models, and formal proofs; the designers of several practical systems appear to be unaware of this. Moreover, we review the consensus protocols in some prominent permissioned blockchain platforms with respect to their fault models and resilience against attacks.
Iddo Bentov, Pavel Hubáček, Tal Moran, Asaf Nadler
We propose Meshcash, a protocol for implementing a permissionless ledger (blockchain) via proofs of work, suitable for use as the underlying consensus mechanism of a cryptocurrency. Unlike most existing proof-of-work based consensus protocols, Meshcash does not rely on leader-election (e.g., the single miner who managed to extend the longest chain). Rather, we use ideas from traditional (permissioned) Byzantine agreement protocols in a novel way to guarantee convergence to a consensus from any starting state. Our construction combines a local “hare” protocol that guarantees fast consensus on recent blocks (but doesn’t, by itself, imply irreversibility) with a global “tortoise” protocol that guarantees irreversibility. Our global protocol also allows the ledger to “self-heal” from arbitrary violations of the security assumptions, reconverging to consensus after the assumptions hold again.
Emmanuelle Anceaume, Romaric Ludinard, Maria Potop-Butucaru, Frédéric Tronel
No abstract is available for this record.
Yang Li, Kai Zheng, Ying Yan, Qi Liu · 5 authors
No abstract is available for this record.
Bernardo David, Peter Gaži, Aggelos Kiayias, Alexander Russell
No abstract is available for this record.
Massimo Bartoletti, Stefano Lande, Alessandro Sebastian Podda
Although the transactions on the Bitcoin blockchain have the main purpose of recording currency transfers, they can also carry a few bytes of metadata. A sequence of transaction metadata forms a subchain of the Bitcoin blockchain, and it can be used to store a tamper-proof execution trace of a smart contract. Except for the trivial case of contracts which admit any trace, in general there may exist inconsistent subchains which represent incorrect contract executions. A crucial issue is how to make it difficult, for an adversary, to subvert the execution of a contract by making its subchain inconsistent. Existing approaches either postulate that subchains are always consistent, or give weak guarantees about their security (for instance, they are susceptible to Sybil attacks). We propose a consensus protocol, based on Proof-of-Stake, that incentivizes nodes to consistently extend the subchain. We empirically evaluate the security of our protocol, and we show how to exploit it as the basis for smart contracts on Bitcoin.
Allan Third, Ilaria Tiddi, Emanuele Bastianelli, Chris St. Valentine · 5 authors
No abstract is available for this record.
Ilya Sergey, Aquinas Hobor
In this paper, we explore remarkable similarities between multi-transactional behaviors of smart contracts in cryptocurrencies such as Ethereum and classical problems of shared-memory concurrency. We examine two real-world examples from the Ethereum blockchain and analyzing how they are vulnerable to bugs that are closely reminiscent to those that often occur in traditional concurrent programs. We then elaborate on the relation between observable contract behaviors and well-studied concurrency topics, such as atomicity, interference, synchronization, and resource ownership. The described contracts-as-concurrent-objects analogy provides deeper understanding of potential threats for smart contracts, indicate better engineering practices, and enable applications of existing state-of-the-art formal verification techniques.
Yossi Gilad, Rotem Hemo, Silvio Micali, Georgios Vlachos · 5 authors
Algorand is a new cryptocurrency that confirms transactions with latency on the order of a minute while scaling to many users. Algorand ensures that users never have divergent views of confirmed transactions, even if some of the users are malicious and the network is temporarily partitioned. In contrast, existing cryptocurrencies allow for temporary forks and therefore require a long time, on the order of an hour, to confirm transactions with high confidence. Algorand uses a new Byzantine Agreement (BA) protocol to reach consensus among users on the next set of transactions. To scale the consensus to many users, Algorand uses a novel mechanism based on Verifiable Random Functions that allows users to privately check whether they are selected to participate in the BA to agree on the next set of transactions, and to include a proof of their selection in their network messages. In Algorand's BA protocol, users do not keep any private state except for their private keys, which allows Algorand to replace participants immediately after they send a message. This mitigates targeted attacks on chosen participants after their identity is revealed. We implement Algorand and evaluate its performance on 1,000 EC2 virtual machines, simulating up to 500,000 users. Experimental results show that Algorand confirms transactions in under a minute, achieves 125x Bitcoin's throughput, and incurs almost no penalty for scaling to more users.
Sergi Delgado-Segura, Cristina Pérez‐Solà, Guillermo Navarro‐Arribas, Jordi Herrera‐Joancomartí
On-line commercial transactions involve an inherent mistrust between participant parties since, sometimes, no previous relation exists between them. Such mistrust may be a deadlock point in a trade transaction where the buyer does not want to perform the payment until the seller sends the goods and the seller does not want to do so until the buyer pays for the purchase. In this paper we present a fair protocol for data trading where the commercial deal, in terms of delivering the data and performing the payment, is atomic, since the seller cannot redeem the payment unless the buyer obtains the data and the buyer cannot obtain the data without performing the payment. The protocol is based on Bitcoin scripting language and the fairness of the protocol can be probabilistically enforced.
Massimo Bartoletti, Livio Pompianu
The Bitcoin protocol allows to save arbitrary data on the blockchain through a special instruction of the scripting language, called OP_RETURN. A growing number of protocols exploit this feature to extend the range of applications of the Bitcoin blockchain beyond transfer of currency. A point of debate in the Bitcoin community is whether loading data through OP_RETURN can negatively affect the performance of the Bitcoin network with respect to its primary goal. This paper is an empirical study of the usage of OP_RETURN over the years. We identify several protocols based on OP_RETURN, which we classify by their application domain. We measure the evolution in time of the usage of each protocol, the distribution of OP_RETURN transactions by application domain, and their space consumption.
Christian Badertscher, Ueli Maurer, Daniel Tschudi, Vassilis Zikas
Abstract Bitcoin is one of the most prominent examples of a distributed cryptographic protocol that is extensively used in reality. Nonetheless, existing security proofs are property-based, and as such they do not support composition. In this work, we put forth a universally composable treatment of the Bitcoin protocol. We specify the goal that Bitcoin aims to achieve as an instance of a parameterizable ledger functionality and present a UC abstraction of the Bitcoin blockchain protocol. Our ideal functionality is weaker than the first proposed candidate by Kiayias, Zhou, and Zikas [EUROCRYPT’16], but unlike the latter suggestion, which is arguably not implementable by the UC Bitcoin protocol, we prove that the one proposed here is securely UC-realized by the protocol assuming access to a global clock, to model time-based executions, a random oracle, to model hash functions, and an idealized network, to model message dissemination. We further show how known property-based approaches can be cast as special instances of our treatment and how their underlying assumptions can be cast in UC as part of the setup functionalities and without restricting the environment or the adversary.
Juan A. Garay, Aggelos Kiayias, Nikos Leonardos
No abstract is available for this record.
Ittay Eyal
The financial technology (FinTech) sector sees high potential value in cryptocurrency blockchain protocols, or distributed-ledger technology (DLT). However, the requirements and guarantees of blockchains for cryptocurrencies do not match those of FinTech-from transaction throughput to security primitives and privacy. The author explores how blockchain research beyond Bitcoin is closing these gaps and some of the challenges that remain.
Wenting Li, Sébastien Andreina, Jens-Matthias Bohli, Ghassan Karame
No abstract is available for this record.
Lakshmi Siva Sankar, M. Sindhu, M. Sethumadhavan
Blockchain is a distributed, transparent, immutable ledger. Consensus protocol forms the core of blockchain. They decide how a blockchain works. With the advent of new possibilities in blockchain technology, researchers are keen to find a well-optimized Byzantine fault tolerant consensus protocol. Creating a global consensus protocol or tailoring a cross-platform plug and play software application for implementation of various consensus protocols are ideas of huge interest. Stellar Consensus Protocol (SCP) is considered to be a global consensus protocol and promises to be Byzantine Fault Tolerant (BFT) by bringing with it the concept of quorum slices and federated byzantine fault tolerance. This consensus's working and its comparison with other protocols that were earlier proposed are analyzed here. Also, hyperledger an open-source project by Linux Foundation which includes implementing the concept of practical byzantine fault tolerance and also a platform where various other consensus protocols and blockchain applications can be deployed in a plug and play manner is also being discussed here. This paper focuses on analyzing these consensus protocols already proposed and their feasibility and efficiency in meeting the characteristics they propose to provide.
Christopher Natoli, Vincent Gramoli
In this paper, we identify a new form of attack, called the Balance attack, against proof-of-work blockchain systems. The novelty of this attack consists of delaying network communications between multiple subgroups of nodes with balanced mining power. Our theoretical analysis captures the precise tradeoff between the network delay and the mining power of the attacker needed to double spend in Ethereum with high probability. We quantify our probabilistic analysis with statistics taken from the R3 consortium, and show that a single machine needs 20 minutes to attack the consortium. Finally, we run an Ethereum private chain in a distributed system with similar settings as R3 to demonstrate the feasibility of the approach, and discuss the application of the Balance attack to Bitcoin. Our results clearly confirm that main proof-of-work blockchain protocols can be badly suited for consortium blockchains.
Johnny Dilley, Andrew Poelstra, Jonathan Wilkins, Marta Piekarska · 6 authors
Bitcoin, the first peer-to-peer electronic cash system, opened the door to permissionless, private, and trustless transactions. Attempts to repurpose Bitcoin's underlying blockchain technology have run up against fundamental limitations to privacy, faithful execution, and transaction finality. We introduce \emph{Strong Federations}: publicly verifiable, Byzantine-robust transaction networks that facilitate movement of any asset between disparate markets, without requiring third-party trust. \emph{Strong Federations} enable commercial privacy, with support for transactions where asset types and amounts are opaque, while remaining publicly verifiable. As in Bitcoin, execution fidelity is cryptographically enforced; however, \emph{Strong Federations} significantly lower capital requirements for market participants by reducing transaction latency and improving interoperability. To show how this innovative solution can be applied today, we describe \emph{\liquid}: the first implementation of \emph{Strong Federations} deployed in a Financial Market.
Ittai Abraham, Dahlia Malkhi, Kartik Nayak, Ling Ren · 5 authors
The decentralized cryptocurrency Bitcoin has experienced great success but also encountered many challenges. One of the challenges has been the long confirmation time. Another challenge is the lack of incentives at certain steps of the protocol, raising concerns for transaction withholding, selfish mining, etc. To address these challenges, we propose Solida, a decentralized blockchain protocol based on reconfigurable Byzantine consensus augmented by proof-of-work. Solida improves on Bitcoin in confirmation time, and provides safety and liveness assuming the adversary control less than (roughly) one-third of the total mining power.
Ittai Abraham, Dahlia Malkhi, Kartik Nayak, Ling Ren · 5 authors
No abstract is available for this record.
Joshua Lind, Ittay Eyal, Peter Pietzuch, Emin Gün Sirer
Blockchain protocols are inherently limited in transaction throughput and latency. Recent efforts to address performance and scale blockchains have focused on off-chain payment channels. While such channels can achieve low latency and high throughput, deploying them securely on top of the Bitcoin blockchain has been difficult, partly because building a secure implementation requires changes to the underlying protocol and the ecosystem. We present Teechan, a full-duplex payment channel framework that exploits trusted execution environments. Teechan can be deployed securely on the existing Bitcoin blockchain without having to modify the protocol. It: (i) achieves a higher transaction throughput and lower transaction latency than prior solutions; (ii) enables unlimited full-duplex payments as long as the balance does not exceed the channel's credit; (iii) requires only a single message to be sent per payment in any direction; and (iv) places at most two transactions on the blockchain under any execution scenario. We have built and deployed the Teechan framework using Intel SGX on the Bitcoin network. Our experiments show that, not counting network latencies, Teechan can achieve 2,480 transactions per second on a single channel, with sub-millisecond latencies.
Adiseshu Hari, T. V. Lakshman
Existing security mechanisms for managing the Internet infrastructural resources like IP addresses, AS numbers, BGP advertisements and DNS mappings rely on a Public Key Infrastructure (PKI) that can be potentially compromised by state actors and Advanced Persistent Threats (APTs). Ideally the Internet infrastructure needs a distributed and tamper-resistant resource management framework which cannot be subverted by any single entity. A secure, distributed ledger enables such a mechanism and the blockchain is the best known example of distributed ledgers.
Andrew Miller, Yu Xia, Kyle Croman, Elaine Shi · 5 authors
The surprising success of cryptocurrencies has led to a surge of interest in deploying large scale, highly robust, Byzantine fault tolerant (BFT) protocols for mission-critical applications, such as financial transactions. Although the conventional wisdom is to build atop a (weakly) synchronous protocol such as PBFT (or a variation thereof), such protocols rely critically on network timing assumptions, and only guarantee liveness when the network behaves as expected. We argue these protocols are ill-suited for this deployment scenario. We present an alternative, HoneyBadgerBFT, the first practical asynchronous BFT protocol, which guarantees liveness without making any timing assumptions. We base our solution on a novel atomic broadcast protocol that achieves optimal asymptotic efficiency. We present an implementation and experimental results to show our system can achieve throughput of tens of thousands of transactions per second, and scales to over a hundred nodes on a wide area network. We even conduct BFT experiments over Tor, without needing to tune any parameters. Unlike the alternatives, HoneyBadgerBFT simply does not care about the underlying network.