Emerging smart contract systems over decentralized cryptocurrencies allow mutually distrustful parties to transact safely without trusted third parties. In the event of contractual breaches or aborts, blockchain ensures that honest obtain commensurate compensation. Existing systems, however, lack transactional privacy. All transactions, including flow money between pseudonyms and amount transacted, are exposed on blockchain. We present Hawk, a system does not store financial transactions in...

Bit coin has emerged as the most successful cryptographic currency in history. Within two years of its quiet launch 2009, grew to comprise billions dollars economic value despite only cursory analysis system's design. Since then a growing literature identified hidden-but-important properties system, discovered attacks, proposed promising alternatives, and singled out difficult future challenges. Meanwhile large vibrant open-source community deployed numerous modifications extensions. We...

Visual information pervades our environment. Vision is used to decide everything from what we want eat at a restaurant and which bus route take whether clothes match how long until the milk expires. Individually, inability interpret such visual nuisance for blind people who often have effective, if inefficient, work-arounds overcome them. Collectively, however, they can make less independent. Specialized technology addresses some problems in this space, but automatic approaches cannot yet...

The lack of access to visual information like text labels, icons, and colors can cause frustration decrease independence for blind people. Current technology uses automatic approaches address some problems in this space, but the is error-prone, limited scope, quite expensive. In paper, we introduce VizWiz, a talking application mobile phones that offers new alternative answering questions nearly real-time - asking multiple people on web. To support quickly, general approach intelligently...

Selfish mining, originally discovered by Eyal et al. [9], is a well-known attack where selfish miner, under certain conditions, can gain disproportionate share of reward deviating from the honest behavior. In this paper, we expand mining strategy space to include novel "stubborn" strategies that, for large range parameters, earn miner more revenue. Consequently, show that not (in general) optimal. Further, how further amplify its non-trivially composing attacks with network-level eclipse...

Bit coin is widely regarded as the first broadly successful e-cash system. An oft-cited concern, though, that mining coins wastes computational resources. Indeed, coin's underlying mechanism, which we call a scratch-off puzzle (SOP), involves continuously attempting to solve puzzles have no intrinsic utility. We propose modification repurposes its resources achieve more useful goal: distributed storage of archival data. our new scheme Perm coin. Unlike and proposed alternatives, requires...

Abstract Monero is a privacy-centric cryptocurrency that allows users to obscure their transactions by including chaff coins, called “mixins,” along with the actual coins they spend. In this paper, we empirically evaluate two weaknesses in Monero’s mixin sampling strategy. First, about 62% of transaction inputs one or more mixins are vulnerable “chain-reaction” analysis - is, real input can be deduced elimination. Second, sampled such way easily distinguished from age distribution; short,...

Ethereum, the second-largest cryptocurrency valued at a peak of $138 billion in 2018, is decentralized, Turing-complete computing platform. Although stability and security Ethereum---and blockchain systems general---have been widely-studied, most analysis has focused on application level features these such as cryptographic mining challenges, smart contract semantics, or block operators. Little attention paid to underlying peer-to-peer (P2P) networks that are responsible for information...

Blind people face a number of challenges when interacting with their environments because so much information is encoded visually. Text pervasively used to label objects, colors carry special significance, and items can easily become lost in surroundings that cannot be quickly scanned. Many tools seek help blind solve these problems by enabling them query for additional information, such as color or text shown on the object. In this paper we argue many useful may better solved directly...

An implicit goal of Bitcoin's reward structure is to diffuse network influence over a diverse, decentralized population individual participants. Indeed, security claims rely on no single entity wielding sufficiently large portion the network's overall computational power. Unfortunately, rather than participating independently, most Bitcoin miners join coalitions called mining pools in which central pool administrator largely directs pool's activity, leading consolidation Recently, largest...

The Nintendo Wii Remote (Wiimote) has served as an input device in 3D user interfaces (3DUIs) but differs from the general-purpose hardware typically found research labs and commercial applications. Despite this, no one systematically evaluated terms of what it offers 3DUI designers. Experience with Wiimote indicates that it's imperfect harbinger a new class spatially convenient devices, classified spatial data, functionality, commodity design. This tutorial presents techniques for using...

This study evaluates the effectiveness of an AR-based context-aware assembly support system with AR visualization modes proposed in object assembly. Although many systems have been proposed, few keep track status real-time and automatically recognize error completion states at each step. Naturally, such remains unexplored. Our test-bed displays guidance information detection corresponding to recognized context building block (LEGO) A user wearing a head mounted display (HMD) can intuitively...

Recent work has demonstrated significant anonymity vulnerabilities in Bitcoin's networking stack. In particular, the current mechanism for broadcasting Bitcoin transactions allows third-party observers to link IP addresses that originated them. This lays groundwork low-cost, large-scale deanonymization attacks. this work, we present Dandelion++, a first-principles defense against attacks with near-optimal information-theoretic guarantees. Dandelion++ builds upon recent proposal called...

An authenticated data structure (ADS) is a whose operations can be carried out by an untrusted prover, the results of which verifier efficiently check as authentic. This done having prover produce compact proof that along with each operation's result. ADSs thus support outsourcing maintenance and processing tasks to servers without loss integrity. Past work on has focused particular structures (or limited classes structures), one at time, often only for operations.

We present cryptocurrency-based lottery protocols that do not require any collateral from the players. Previous for this task required a security deposit is O(N2) times larger than bet amount, where N number of Our are based on tournament bracket construction, and only O(logN) rounds. thus represent significant improvement, both because they allow players with little money to participate, time value money. The Ethereum-based implementation our highly efficient. Bitcoin requires an O(2N)...