Follow blockchain research across journals, conferences, and preprint repositories.
9,005 results · page 321 of 376
FC 2017 Sliema, Michael 1974- Brenner, Kurt Rohloff, Joseph Bonneau · 12 authors
No abstract is available for this record.
Jonathan Bootle, Andrea Cerulli, Pyrros Chaidos, Jens Groth
No abstract is available for this record.
Ari Juels, Ahmed E. Kosba, Elaine Shi
Thanks to their anonymity (pseudonymity) and elimination of trusted intermediaries, cryptocurrencies such as Bitcoin have created or stimulated growth in many businesses and communities. Unfortunately, some of these are criminal, e.g., money laundering, illicit marketplaces, and ransomware. Next-generation cryptocurrencies such as Ethereum will include rich scripting languages in support of smart contracts, programs that autonomously intermediate transactions. In this paper, we explore the risk of smart contracts fueling new criminal ecosystems. Specifically, we show how what we call criminal smart contracts (CSCs) can facilitate leakage of confidential information, theft of cryptographic keys, and various realworld crimes (murder, arson, terrorism). We show that CSCs for leakage of secrets (a la Wikileaks) are efficiently realizable in existing scripting languages such as that in Ethereum. We show that CSCs for theft of cryptographic keys can be achieved using primitives, such as Succinct Non-interactive ARguments of Knowledge (SNARKs), that are already expressible in these languages and for which efficient supporting language extensions are anticipated. We show similarly that authenticated data feeds, an emerging feature of smart contract systems, can facilitate CSCs for realworld crimes (e.g., property crimes). Our results highlight the urgency of creating policy and technical safeguards against CSCs in order to realize the promise of smart contracts for beneficial goals.
Massimo Bartoletti, Roberto Zunino
An active research trend is to exploit the consensus mechanism of cryptocurrencies to secure the execution of distributed applications. In particular, some recent works have proposed fair lotteries which work on Bitcoin. These protocols, however, require a deposit from each player which grows quadratically with the number of players. We propose a fair lottery on Bitcoin which only requires a constant deposit.
Melissa Chase, Chaya Ganesh, Payman Mohassel
Practical anonymous credential systems are generally built around sigma-protocol ZK proofs. This requires that credentials be based on specially formed signatures. Here we ask whether we can instead use a standard say, RSA, or ECDSA signature that includes formatting and hashing messages, as a credential, and still provide privacy. Existing techniques do not provide efficient solutions for proving knowledge of such a signature: On the one hand, ZK proofs based on garbled circuits Jawurek et al. 2013 give efficient proofs for checking formatting of messages and evaluating hash functions. On the other hand they are expensive for checking algebraic relations such as RSA or discrete-log, which can be done efficiently with sigma protocols. We design new constructions obtaining the best of both worlds: combining the efficiency of the garbled circuit approach for non-algebraic statements and that of sigma protocols for algebraic ones. We then discuss how to use these as building-blocks to construct privacy-preserving credential systems based on standard RSA and ECDSA signatures. Other applications of our techniques include anonymous credentials with more complex policies, the ability to efficiently switch between commitments and signatures in different groups, and secure two-party computation on committed/signed inputs.
Broadbent Anne, Zhengfeng Ji, Song Fang, Watrous John
Prior work has established that all problems in NP admit classical zero-knowledge proof systems, and under reasonable hardness assumptions for quantum computations, these proof systems can be made secure against quantum attacks. We prove a result representing a further quantum generalization of this fact, which is that every problem in the complexity class QMA has a quantum zero-knowledge proof system. More specifically, assuming the existence of an unconditionally binding and quantum computationally concealing commitment scheme, we prove that every problem in the complexity class QMA has a quantum interactive proof system that is zero-knowledge with respect to efficient quantum computations. Our QMA proof system is sound against arbitrary quantum provers, but only requires an honest prover to perform polynomial-time quantum computations, provided that it holds a quantum witness for a given instance of the QMA problem under consideration. The proof system relies on a new variant of the QMA-complete local Hamiltonian problem in which the local terms are described by Clifford operations and standard basis measurements. We believe that the QMA-completeness of this problem may have other uses in quantum complexity.
Aggelos Kiayias, Ioannis Konstantinou, Alexander Russell, Bernardo David · 5 authors
No abstract is available for this record.
WacĆaw Banasik, Stefan Dziembowski, Daniel Malinowski
No abstract is available for this record.
Rachid El Bansarkhani, Jan Egbert Sturm
No abstract is available for this record.
Ilias Giechaskiel, Cas Cremers, Kasper Rasmussen
No abstract is available for this record.
Fan Zhang, Ethan Cecchetti, Kyle Croman, Ari Juels · 5 authors
Smart contracts are programs that execute autonomously on blockchains. Their key envisioned uses (e.g. financial instruments) require them to consume data from outside the blockchain (e.g. stock quotes). Trustworthy data feeds that support a broad range of data requests will thus be critical to smart contract ecosystems. We present an authenticated data feed system called Town Crier (TC). TC acts as a bridge between smart contracts and existing web sites, which are already commonly trusted for non-blockchain applications. It combines a blockchain front end with a trusted hardware back end to scrape HTTPSenabled websites and serve source-authenticated data to relying smart contracts. TC also supports confidentiality. It enables private data requests with encrypted parameters. Additionally, in a generalization that executes smart-contract logic within TC, the system permits secure use of user credentials to scrape access-controlled online data sources. We describe TCâs design principles and architecture and report on an implementation that uses Intelâs recently introduced Software Guard Extensions (SGX) to furnish data to the Ethereum smart contract system. We formally model TC and define and prove its basic security properties in the Universal Composability (UC) framework. Our results include definitions and techniques of general interest relating to resource consumption (Ethereumâs âgasâ fee system) and TCB minimization. We also report on experiments with three example applications. We plan to launch TC soon as an online public service.
Loi Luu, Duc-Hiep Chu, Hrishi Olickel, Prateek Saxena · 5 authors
Cryptocurrencies record transactions in a decentralized data structure called a blockchain. Two of the most popular cryptocurrencies, Bitcoin and Ethereum, support the feature to encode rules or scripts for processing transactions. This feature has evolved to give practical shape to the ideas of smart contracts, or full-fledged programs that are run on blockchains. Recently, Ethereum's smart contract system has seen steady adoption, supporting tens of thousands of contracts, holding millions dollars worth of virtual coins. In this paper, we investigate the security of running smart contracts based on Ethereum in an open distributed network like those of cryptocurrencies. We introduce several new security problems in which an adversary can manipulate smart contract execution to gain profit. These bugs suggest subtle gaps in the understanding of the distributed semantics of the underlying platform. As a refinement, we propose ways to enhance the operational semantics of Ethereum to make contracts less vulnerable. For developers writing contracts for the existing Ethereum system, we build a symbolic execution tool called Oyente to find potential security bugs. Among 19, 336 existing Ethereum contracts, Oyente flags 8, 833 of them as vulnerable, including the TheDAO bug which led to a 60 million US dollar loss in June 2016. We also discuss the severity of other attacks for several case studies which have source code available and confirm the attacks (which target only our accounts) in the main Ethereum network.
Yonatan Sompolinsky, Yoad Lewenberg, Aviv Zohar
No abstract is available for this record.
Joseph Bonneau
No abstract is available for this record.
Karl WĂŒst, Arthur Gervais
No abstract is available for this record.
Nicola Atzei, Massimo Bartoletti, Tiziana Cimoli
No abstract is available for this record.
Jordi HerreraâJoancomartĂ, Cristina PĂ©rezâSolĂ
No abstract is available for this record.
Malte Möser, Ittay Eyal, Emin GĂŒn Sirer
No abstract is available for this record.
Tim Ruffing, Pedro Moreno-SĂĄnchez, Aniket Kate
Author(s): Tim Ruffing, Pedro Moreno-Sanchez, Aniket Kate Download: Paper (PDF) Date: 27 Feb 2017 Document Type: Reports Additional Documents: Slides Video Associated Event: NDSS Symposium 2017 Abstract: Starting with Dining Cryptographers networks (DC-nets), several peer-to-peer (P2P) anonymous communication protocols have been proposed. However, despite their strong anonymity guarantees, none of them have been employed in practice so far: Most ⊠Continued
Alin Tomescu, Srinivas Devadas
© 2017 IEEE. We present Catena, an efficiently-verifiable Bitcoinwitnessing scheme. Catena enables any number of thin clients, such as mobile phones, to efficiently agree on a log of application-specific statements managed by an adversarial server. Catenaimplements a log as an OP-RETURN transaction chain andprevents forks in the log by leveraging Bitcoin's security againstdouble spends. Specifically, if a log server wants to equivocate ithas to double spend a Bitcoin transaction output. Thus, Catenalogs are as hard to fork as the Bitcoin blockchain: an adversarywithout a large fraction of the network's computational powercannot fork Bitcoin and thus cannot fork a Catena log either. However, different from previous Bitcoin-based work, Catenadecreases the bandwidth requirements of log auditors from 90GB to only tens of megabytes. More precisely, our clients onlyneed to download all Bitcoin block headers (currently less than35 MB) and a small, 600-byte proof for each statement in a block. We implement Catena in Java using the bitcoinj library and use itto extend CONIKS, a recent key transparency scheme, to witnessits public-key directory in the Bitcoin blockchain where it can beefficiently verified by auditors. We show that Catena can securemany systems today, such as public-key directories, Tor directoryservers and software transparency schemes.
Rosario Gennaro, Steven Goldfeder, Arvind Narayanan
No abstract is available for this record.
Ethan Heilman, Foteini Baldimtsi, Sharon Goldberg
Although Bitcoin is often perceived to be an anonymous currency, research has shown that a userâs Bitcoin transactions can be linked to compromise the userâs anonymity. We present solutions to the anonymity problem for both transactions on Bitcoinâs blockchain and off the blockchain (in so called micropayment channel networks). We use an untrusted third party to issue anonymous vouchers which users redeem for Bitcoin. Blind signatures and Bitcoin transaction contracts (aka smart contracts) ensure the anonymity and fairness during the bitcoin â voucher exchange. Our schemes are practical, secure and anonymous.
Roman Beck, Jacob Stenum Czepluch, Nikolaj Lollike, Simon Malone
No abstract is available for this record.
Giuseppe Ateniese, Bernardo Magri, Daniele Venturi, Ewerton R. Andrade
We put forward a new framework that makes it possible to re-write or compress the content of any number of blocks in decentralized services exploiting the blockchain technology. As we argue, there are several reasons to prefer an editable blockchain, spanning from the necessity to remove inappropriate content and the possibility to support applications requiring re-writable storage, to "the right to be forgotten." Our approach generically leverages so-called chameleon hash functions (Krawczyk and Rabin, NDSS '00), which allow determining hash collisions efficiently, given a secret trapdoor information. We detail how to integrate a chameleon hash function in virtually any blockchain-based technology, for both cases where the power of redacting the blockchain content is in the hands of a single trusted entity and where such a capability is distributed among several distrustful parties (as is the case with Bitcoin). We also report on a proof-of-concept implementation of a redactable blockchain, building on top of Nakamoto's Bitcoin core. The prototype only requires minimal changes to the way current client software interprets the information stored in the blockchain and to the current blockchain, block, or transaction structures. Moreover, our experiments show that the overhead imposed by a redactable blockchain is small compared to the case of an immutable one.