Follow blockchain research across journals, conferences, and preprint repositories.
9,005 results · page 311 of 376
Robert K. Cunningham, Benjamin Fuller, Sophia Yakoubov
No abstract is available for this record.
Zhongxiang Zheng, Chunhuan Zhao, Haining Fan, Xiaoyun Wang
No abstract is available for this record.
Lei Xu, Lin Chen, Nolan Shah, Zhimin Gao · 6 authors
Since Internet based applications have become the norm for most users, security has become a bigger concern than ever before, especially for applications like social networking and cloud based storage. Access control is one of the key techniques that can mitigate security concerns for web based applications. However, most existing access control mechanisms require a trusted party, which are vulnerable to many threats including malicious insiders and single point failure. In response to these challenges, we propose DL-BAC, a novel access control system based on the distributed ledger. DL-BAC robustly enforces access control policies without depending on a single trusted party. We also provide an extension of DL-BAC that is privacy respecting and evaluate the performance of DL-BAC to show its practicability.
Gorjan Alagic, Yfke Dulek, Christian Schaffner, Florian Speelman
Fully-homomorphic encryption (FHE) enables computation on encrypted data while maintaining secrecy. Recent research has shown that such schemes exist even for quantum computation. Given the numerous applications of classical FHE (zero-knowledge proofs, secure two-party computation, obfuscation, etc.) it is reasonable to hope that quantum FHE (or QFHE) will lead to many new results in the quantum setting. However, a crucial ingredient in almost all applications of FHE is circuit verification. Classically, verification is performed by checking a transcript of the homomorphic computation. Quantumly, this strategy is impossible due to no-cloning. This leads to an important open question: can quantum computations be delegated and verified in a non-interactive manner? In this work, we answer this question in the affirmative, by constructing a scheme for QFHE with verification (vQFHE). Our scheme provides authenticated encryption, and enables arbitrary polynomial-time quantum computations without the need of interaction between client and server. Verification is almost entirely classical; for computations that start and end with classical states, it is completely classical. As a first application, we show how to construct quantum one-time programs from classical one-time programs and vQFHE.
Yashvanth Kondi, Arpita Patra
No abstract is available for this record.
Rishab Goyal, Vipul Goyal
Blockchain technology has the potential to disrupt how cryptography is done. In this work, we propose to view blockchains as an “enabler”, much like indistinguishability obfuscation [5, 23, 46] or one-way functions, for building a variety of cryptographic systems. Our contributions in this work are as follows: 1. A Framework for Proof-of-Stake based Blockchains: We provide an abstract framework for formally analyzing and defining useful security properties for Proof-of-Stake (POS) based blockchain protocols. Interestingly, for some of our applications, POS based protocols are more suitable. We believe our framework and assumptions would be useful in building applications on top of POS based blockchain protocols even in the future. 2. Blockchains as an Alternative to Trusted Setup Assumptions in Cryptography: A trusted setup, such as a common reference string (CRS) has been used to realize numerous systems in cryptography. The paragon example of a primitive requiring trusted setup is a non-interactive zero-knowledge (NIZK) system. We show that already existing blockchains systems including Bitcoin, Ethereum etc. can be used as a foundation (instead of a CRS) to realize NIZK systems. The novel aspect of our work is that it allows for utilizing an already existing (and widely trusted) setup rather than proposing a new one. Our construction does not require any additional functionality from the miners over the already existing ones, nor do we need to modify the underlying blockchain protocol. If an adversary can violate the security of our NIZK, it could potentially also take over billions of dollars worth of coins in the Bitcoin, Ethereum or any such cryptocurrency! We believe that such a “trusted setup” represents significant progress over using CRS published by a central trusted party. Indeed, NIZKs could further serve as a foundation for a variety of other cryptographic applications such as round efficient secure computation [33, 36]. 3. One-time programs and pay-per use programs: Goldwasser et al. [29] introduced the notion of one time program and presented a construction using tamper-proof hardware. As noted by Goldwasser et al. [29], clearly a one-time program cannot be solely software based, as software can always be copied and run again. While there have been a number of follow up works [4, 6, 30], there are indeed no known constructions of one-time programs which do not rely on self destructing tamper-proof hardware (even if one uses trusted setup or random oracles). Somewhat surprisingly, we show that it is possible to base one-time programs on POS based blockchain systems without relying on trusted hardware. Our ideas do not seem to translate over to Proof-of-Work (POW) based blockchains. We also introduce the notion of pay-per-use programs which is simply a contract between two parties — service provider and customer. A service provider supplies a program such that if the customer transfers a specific amount of coins to the provider, it can evaluate the program on any input of its choice once, even if the provider is offline. This is naturally useful in a subscription based model where your payment is based on your usage.
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.
Wentao Zhang, Qianhong Wu, Bo Qin, Tianxu Han · 7 authors
No abstract is available for this record.
Sanjam Garg, Akshayaram Srinivasan
In this paper, we initiate the study of garbled protocols — a generalization of Yaos garbled circuits construction to distributed protocols. More specifically, in a garbled protocol construction, each party can independently generate a garbled protocol component along with pairs of input labels. Additionally, it generates an encoding of its input. The evaluation procedure takes as input the set of all garbled protocol components and the labels corresponding to the input encodings of all parties and outputs the entire transcript of the distributed protocol.We provide constructions for garbling arbitrary protocols based on standard computational assumptions on bilinear maps (in the common random string model). Next, using garbled protocols we obtain a general compiler that compresses any arbitrary round multiparty secure computation protocol into a two-round UC secure protocol. Previously, two-round multiparty secure computation protocols were only known assuming witness encryption or learning-with errors. Benefiting from our generic approach we also obtain protocols (i) for the setting of random access machines (RAM programs) while keeping communication and computational costs proportional to running times, while (ii) making only a black-box use of the underlying group, eliminating the need for any expensive non-black-box group operations. Our results are obtained by a simple but powerful extension of the non-interactive zero-knowledge proof system of Groth, Ostrovsky and Sahai [Journal of ACM, 2012].
ASIACRYPT 2017 Hongkong, Tsuyoshi Takagi, Thomas Peyrin
No abstract is available for this record.
Roberto Metere, Changyu Dong
Aiming for strong security assurance, recently there has been an increasing interest in formal verification of cryptographic constructions. This paper presents a mechanised formal verification of the popular Pedersen commitment protocol, proving its security properties of correctness, perfect hiding, and computational binding. To formally verify the protocol, we extended the theory of EasyCrypt, a framework which allows for reasoning in the computational model, to support the discrete logarithm and an abstraction of commitment protocols. Commitments are building blocks of many cryptographic constructions, for example, verifiable secret sharing, zero-knowledge proofs, and e-voting. Our work paves the way for the verification of those more complex constructions.
Patrick McCorry, Ethan Heilman, Andrew Miller
No abstract is available for this record.
Areej M. Abduldaim
Innovative idea using ring theory is raised to build a new algorithm for zero knowledge (ZK) cryptosystem. In this paper we introduce an algorithm for zero knowledge protocol based on a specific kind of rings named weak Armendariz. On the other hand, the aim of this paper focuses on the category of noncommutative algebraic structures to describe a new algebraic scheme of zero knowledge proof using weak Armendariz rings. As a result, we employ for the first time weak Armendariz rings in the science of cryptographic which regards as a new application of this class of rings. Finally, we present a novel idea combining between abstract algebra and cryptography.
Jorge Bernal Bernabé, José L. Hernández-Ramos, Antonio Skármeta
Security and privacy concerns are becoming an important barrier for large scale adoption and deployment of the Internet of Things. To address this issue, the identity management system defined herein provides a novel holistic and privacy-preserving solution aiming to cope with heterogeneous scenarios that requires both traditional online access control and authentication, along with claim-based approach for M2M (machine to machine) interactions required in IoT. It combines a cryptographic approach for claim-based authentication using the Idemix anonymous credential system, together with classic IdM mechanisms by relying on the FIWARE IdM (Keyrock). This symbiosis endows the IdM system with advanced features such as privacy-preserving, minimal disclosure, zero-knowledge proofs, unlikability, confidentiality, pseudonymity, strong authentication, user consent, and offline M2M transactions. The IdM system has been specially tailored for the Internet of Things bearing in mind the management of both users’ and smart objects’ identity. Moreover, the IdM system has been successfully implemented, deployed, and tested in the scope of SocIoTal European research project.
Dominik Harz
Blockchains address trust through cryptography and consensus. Bitcoin is the first digital currency without trusted agents. Ethereum extends this technology by enabling agents on a blockchain, via smart contracts. However, a systemic trust model for smart contracts in blockchains is missing. This thesis describes the ecosystem of smart contracts as an open multi-agent system. A trust model introduces social control through deposits and review agents. Trust-related attributes are quantified in 2,561 smart contracts from GitHub. Smart contracts employ a mean of three variables and functions and one in ten has a security-related issue. Moreover, blockchains restrict computation tasks. Resolving these restrictions while maintaining trust requires verifiable computation. An algorithm for verifiable computation is developed and implemented in Solidity. It uses an arbiter enforcing the algorithm, computation services providing and verifying solutions, and a judge assessing solutions. Experiments are performed with 1000 iterations for one to six verifiers with a cheater prior probability of 30%, 50%, and 70%. The algorithm shows linear complexity for integer multiplication. The verification depends on cheater prior probability and amount of verifiers. In the experiments, six verifiers are sufficient to detect all cheaters for the three prior probabilities.
A Outchakoucht H Es-Samaali, Nn Van, R Nakagawa S Kodama
No abstract is available for this record.
Sean Bowe, Ariel Gabizon, Matthew Green
Recent efficient constructions of zero-knowledge Succinct Non-interactive Arguments of Knowledge (zk-SNARKs), require a setup phase in which a common-reference string (CRS) with a certain structure is generated. This CRS is sometimes referred to as the public parameters of the system, and is used for constructing and verifying proofs. A drawback of these constructions is that whomever runs the setup phase subsequently possesses trapdoor information enabling them to produce fraudulent pseudoproofs.
Yuqin Xu, Shangli Zhao, Lanju Kong, Yongqing Zheng · 6 authors
No abstract is available for this record.
Jesper Buus Nielsen
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.
Rafaël del Pino, Vadim Lyubashevsky
For a linear function f, a vector \(\mathbf{x}\) with small coefficients, and a vector \(y=f(\mathbf{x})\), we would like to be able to give a zero-knowledge proof for the knowledge of an \(\mathbf{x}'\) with small coefficients that satisfies \(f(\mathbf{x}')=y\). This is a common scenario in lattice-based cryptography, and there is currently no satisfactory solution for this problem. All known protocols are built via the repetition of a basic protocol that only has constant (1/2 or 2/3) soundness error. This implies that the communication complexity of the final protocol will be at least a factor of k larger than that of the basic one, where k is the security parameter.
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.
Hitoshi Okada, Shigeichiro Yamasaki, Vanessa Bracamonte
The potential of blockchain technology has received attention in the area of FinTech - the combination of finance and technology. Blockchain technology was first introduced as the technology behind the Bitcoin decentralized virtual currency, but there is the expectation that its characteristics of accurate and irreversible data transfer in a decentralized P2P network could make other applications possible. Although a precise definition of blockchain technology has not yet been given, it is important to consider how to classify different blockchain systems in order to better understand their potential and limitations. The goal of this paper is to add to the discussion on blockchain technology by proposing a classification based on two dimensions external to the system: (1) existence of an authority (without an authority and under an authority) and (2) incentive to participate in the blockchain (market-based and non-market-based). The combination of these elements results in four types of blockchains. We define these dimensions and describe the characteristics of the blockchain systems belonging to each classification.
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.