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2,611 results · page 96 of 109
Yashvanth Kondi, Arpita Patra
No abstract is available for this record.
Rami Khalil, Arthur Gervais
Scaling the transaction throughput of decentralized blockchain ledgers such as Bitcoin and Ethereum has been an ongoing challenge. Two-party duplex payment channels have been designed and used as building blocks to construct linked payment networks, which allow atomic and trust-free payments between parties without exhausting the resources of the blockchain. \n \nOnce a payment channel, however, is depleted (e.g., because transactions were mostly unidirectional) the channel would need to be closed and re-funded to allow for new transactions. Users are envisioned to entertain multiple payment channels with different entities, and as such, instead of refunding a channel (which incurs costly on-chain transactions), a user should be able to leverage his existing channels to rebalance a poorly funded channel. \n \nTo the best of our knowledge, we present the first solution that allows an arbitrary set of users in a payment channel network to securely rebalance their channels, according to the preferences of the channel owners. Except in the case of disputes (similar to conventional payment channels), our solution does not require on-chain transactions and therefore increases the scalability of existing blockchains. In our security analysis, we show that an honest participant cannot lose any of its funds while rebalancing. We finally provide a proof of concept implementation and evaluation for the Ethereum network.
Svetlana Abramova, Pascal Schöttle, Rainer Böhme
No abstract is available for this record.
Syeda Sumbul Hossain, Samen Anjum Arani, Md. Tanvir Rahman, Touhid Bhuiyan · 6 authors
In every nation, democratic elections are a momentous and weighty occurrence, and the voting system that is now in place requires the use of ballots or electronic voting machines (EVM). Transparency, poor turnout, vote manipulation, distrust of electoral organizations, fabrication of unique IDs (voting party IDs), and delays in posting results are some of the issues that arise as a result of these procedures. The matter of safety is of the utmost importance. When considering the installation of a computerized voting system, voter confidentiality has always been one of the most important concerns. There is no question regarding the system's capability to secure itself in contrast to prospective assaults and safeguard data in the face of such big choices. Utilization of blockchain technology is one approach that might be taken to resolve security concerns. The blockchain technology has an endless number of different uses that might be implemented. The technology known as blockchain is a distributed ledger that makes it possible for peer-to-peer networks all over the world to handle digital assets. In this context, distributed ledger technology represents an intriguing development. A grouping of all transactions is referred to as a block. Immutability, decentralisation, security, transparency, and anonymity are some of the outstanding properties offered by blockchain technology. The combination of blockchain technology with smart contracts has shown promise as a viable option for the development of trustworthy and open-source electronic voting systems. In this article, we demonstrate how to use blockchain technology with the help of a wallet and the Solidity programming language to build an electronic voting application. The programme was designed as a smart contract for the Ethereum network. In order to avoid having the same person vote twice, the user's wallet will only hold a certain number of tokens (gas), which will be depleted each time the user casts a vote. This article talks about the pros and cons of using blockchain technology. It also shows a practical solution in the form of a web app for voting and analyses its limits.
Muoi Tran, Loi Luu, Min Suk Kang, Iddo Bentov · 5 authors
Bitcoin provides only pseudo-anonymous transactions, which can be exploited to link payers and payees -- defeating the goal of anonymous payments. To thwart such attacks, several Bitcoin mixers have been proposed, with the objective of providing unlinkability between payers and payees. However, existing Bitcoin mixers can be regarded as either insecure or inefficient. We present Obscuro, a highly efficient and secure Bitcoin mixer that utilizes trusted execution environments (TEEs). With the TEE's confidentiality and integrity guarantees for code and data, our mixer design ensures the correct mixing operations and the protection of sensitive data (i.e., private keys and mixing logs), ruling out coin theft and address linking attacks by a malicious service provider. Yet, the TEE-based implementation does not prevent the manipulation of inputs (e.g., deposit submissions, blockchain feeds) to the mixer, hence Obscuro is designed to overcome such limitations: it (1) offers an indirect deposit mechanism to prevent a malicious service provider from rejecting benign user deposits; and (2) scrutinizes blockchain feeds to prevent deposits from being mixed more than once (thus degrading anonymity) while being eclipsed from the main blockchain branch. In addition, Obscuro provides several unique anonymity features (e.g., minimum mixing set size guarantee, resistant to dropping user deposits) that are not available in existing centralized and decentralized mixers. Our prototype of Obscuro is built using Intel SGX and we demonstrate its effectiveness in Bitcoin Testnet. Our implementation mixes 1000 inputs in just 6.49 seconds, which vastly outperforms all of the existing decentralized mixers.
Bingqing Xia, Dongyao Ji, Gang Yao
No abstract is available for this record.
Rafaël del Pino, Vadim Lyubashevsky, Gregory Neven, Gregor Seiler
We propose a lattice-based electronic voting scheme, EVOLVE (Electronic Voting from Lattices with Verification), which is conjectured to resist attacks by quantum computers. Our protocol involves a number of voting authorities so that vote privacy is maintained as long as at least one of the authorities is honest, while the integrity of the result is guaranteed even when all authorities collude. Furthermore, the result of the vote can be independently computed by any observer. At the core of the protocol is the utilization of a homomorphic commitment scheme with strategically orchestrated zero-knowledge proofs: voters use approximate but efficient "Fiat-Shamir with Aborts" proofs to show the validity of their vote, while the authorities use amortized exact proofs to show that the commitments are well-formed. We also present a novel efficient zero-knowledge proof that one of two lattice-based statements is true (so-called OR proof) and a new mechanism to control the size of the randomness when applying the homomorphism to commitments. We give concrete parameter choices to securely instantiate and evaluate the efficiency of our scheme. Our prototype implementation shows that the voters require $8$ milliseconds to submit a vote of size about $20$KB to each authority and it takes each authority $0.15$ seconds per voter to create a proof that his vote was valid. The size of the vote share that each authority produces is approximately $15$KB per voter, which we believe is well within the practical bounds for a large-scale election.
Foteini Baldimtsi, Jan Camenisch, Maria Dubovitskaya, Anna Lysyanskaya · 7 authors
Membership revocation is essential for cryptographic applications, from traditional PKIs to group signatures and anonymous credentials. Of the various solutions for the revocation problem that have been explored, dynamic accumulators are one of the most promising. We propose Braavos, a new, RSA-based, dynamic accumulator. It has optimal communication complexity and, when combined with efficient zero-knowledge proofs, provides an ideal solution for anonymous revocation. For the construction of Braavos we use a modular approach: we show how to build an accumulator with better functionality and security from accumulators with fewer features and weaker security guarantees. We then describe an anonymous revocation component (ARC) that can be instantiated using any dynamic accumulator. ARC can be added to any anonymous system, such as anonymous credentials or group signatures, in order to equip it with a revocation functionality. Finally, we implement ARC with Braavos and plug it into Idemix, the leading implementation of anonymous credentials. This work resolves, for the first time, the problem of practical revocation for anonymous credential systems.
Sarah Meiklejohn, Rebekah Mercer
Cryptocurrencies allow users to securely transfer money without relying on a trusted intermediary, \nand the transparency of their underlying ledgers also enables public verifiability. This openness, \nhowever, comes at a cost to privacy, as even though the pseudonyms users go by are not linked to their \nreal-world identities, all movement of money among these pseudonyms is traceable. In this paper, \nwe present M¨obius, an Ethereum-based tumbler or mixing service. M¨obius achieves strong notions of \nanonymity, as even malicious senders cannot identify which pseudonyms belong to the recipients to \nwhom they sent money, and is able to resist denial-of-service attacks. It also achieves a much lower \noff-chain communication complexity than all existing tumblers, with senders and recipients needing \nto send only two initial messages in order to engage in an arbitrary number of transactions.
Núria Costa, Ramiro Martínez, Paz Morillo
No abstract is available for this record.
Yi Liu, Qi Wang
No abstract is available for this record.
Bastian Fredriksson
The thesis investigates how a blockchain can be used to build a decentralised public key infrastructure for the web, by proposing a custom federation blockchain relying on honest majority. Our main contribution is the design of a Proof of Stake protocol based on a stake tree, which builds upon an idea called follow-the-satoshi used in previous papers. Digital identities are stored in an authenticated self-balancing tree maintained by blockchain nodes. Our back-of-the-envelope calculations, based on the size of the domain name system, show that the block size must be set to at least 5.2 MB, while each blockchain node with a one-month transaction history would need to store about 243 GB. Thin clients would have to synchronise about 13.6 MB of block headers per year, and download an additional 3.7 KB of proof data for every leaf certificate which is to be checked.
Maged Hamada Ibrahim
No abstract is available for this record.
Benoît Libert, San Ling, Khoa Nguyen, Huaxiong Wang
No abstract is available for this record.
Paul Cruz Jason, Yuichi Kaji
No abstract is available for this record.
Louise Axon, Michael Goldsmith
Conventional public-key infrastructure (PKI) designs using certificate authorities and web-of-trust are not optimal and have security flaws. The properties afforded by the Bitcoin blockchain are a natural solution to some of the problems with PKI - in particular, certificate transparency and elimination of single points-offailure. Proposed blockchain-based PKI designs are built as public ledgers linking identity with public key, providing no privacy. We consider cases requiring privacy-aware PKIs, which do not link identity with public key. We show that blockchain technology can be used to construct a privacy-aware PKI while eliminating some of the problems of conventional PKI, and present PB-PKI, a privacy-aware blockchain-based PKI.
Svein Ølnes, Arild Jansen
No abstract is available for this record.
Cecilia Boschini, Jan Camenisch, Gregory Neven
Advanced cryptographic protocols such as anonymous credentials, voting schemes, and e-cash are typically constructed by suitably combining signature, commitment, and encryption schemes with zero-knowledge proofs. Indeed, a large body of protocols have been constructed in that manner from Camenisch-Lysyanskaya signatures and generalized Schnorr proofs. In this paper, we build a similar framework for lattice-based schemes by presenting a signature and commitment scheme that are compatible with Lyubashevsky’s Fiat-Shamir proofs with abort, currently the most efficient zero-knowledge proofs for lattices. The latter proofs provide a weaker, relaxed form of soundness, i.e., the witnesses that the knowledge extractor can obtain are guaranteed to lie only in a domain that is larger than the one from which the inputs of honest provers need to come. To cope with this soundness problem, we define corresponding notions of relaxed signature and commitment schemes. We demonstrate the flexibility and efficiency of our new primitives by constructing a new lattice-based anonymous attribute token scheme and providing concrete parameters to securely instantiate this scheme.
Zhiqiang Liu, Shuyang Tang, Sherman S. M. Chow, Zhen Liu · 5 authors
Abstract Bitcoin and its underlying blockchain mechanism have been attracting much attention. One of their core innovations, Proof-of-Work (PoW), is notoriously inefficient which potentially motivates a centralization of hash power, defeating the original goal of decentralization. Proof-of-Stake (PoS) is later proposed to replace PoW. However, both PoW and PoS have different inherent advantages and disadvantages, so does Proof-of-Activity (PoA) of Bentov et al. (SIGMETRICS 2014) which only offers limited hybrids of two mechanisms. On the other hand, the hybrid consensus protocol of Pass and Shi (DISC 2017) aims to improve the efficiency by dynamically maintaining a rotating committee. Yet, there are unsatisfactory issues including chain forks and fair committee election. In this paper, we firstly devise a generalized variant of PoW. After that, we leverage our generalized PoW to construct a fork-free hybrid consensus protocol. We further combine our fork-free hybrid consensus mechanism with PoS for a flexible version of PoA with tunable parameters between PoW and PoS. Compared with Bentov et al.’s PoA, our “flexible PoA” improves the efficiency, leading to a more applicable consensus protocol.
Keundug Park, ChangOh Kim, Heung-Youl Youm
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.
Alexander Chepurnoy, Tuyet Duong, Lei Fan, Hong-Sheng Zhou
No abstract is available for this record.
Till Neudecker, Hannes Hartenstein
No abstract is available for this record.
Giulia Fanti, Pramod Viswanath
Recent attacks on Bitcoin's peer-to-peer (P2P) network demonstrated that its transaction-flooding protocols, which are used to ensure network consistency, may enable user deanonymization---the linkage of a user's IP address with her pseudonym in the Bitcoin network. In 2015, the Bitcoin community responded to these attacks by changing the network's flooding mechanism to a different protocol, known as diffusion. However, it is unclear if diffusion actually improves the system's anonymity. In this paper, we model the Bitcoin networking stack and analyze its anonymity properties, both pre- and post-2015. The core problem is one of epidemic source inference over graphs, where the observational model and spreading mechanisms are informed by Bitcoin's implementation; notably, these models have not been studied in the epidemic source detection literature before. We identify and analyze near-optimal source estimators. This analysis suggests that Bitcoin's networking protocols (both pre- and post-2015) offer poor anonymity properties on networks with a regular-tree topology. We confirm this claim in simulation on a 2015 snapshot of the real Bitcoin P2P network topology.