Proceedings of the ACM Workshop on Blockchain, Cryptocurrencies and Contracts最新文献

{"title":"Unraveling Blockchain based Crypto-currency System Supporting Oblivious Transactions: a Formalized Approach","authors":"Lin Chen, Lei Xu, Nolan Shah, Nour Diallo, Zhimin Gao, Yang Lu, W. Shi","doi":"10.1145/3055518.3055528","DOIUrl":"https://doi.org/10.1145/3055518.3055528","url":null,"abstract":"User privacy is an important issue in a blockchain based transaction system. Bitcoin, being one of the most widely used blockchain based transaction system, fails to provide enough protection on users' privacy. Many subsequent studies focus on establishing a system that hides the linkage between the identities (pseudonyms) of users and the transactions they carry out in order to provide a high level of anonymity. Examples include Zerocoin, Zerocash and so on. It thus becomes an interesting question whether such new transaction systems do provide enough protection on users' privacy. In this paper, we propose a novel and effective approach for de-anonymizing these transaction systems by leveraging information in the system that is not directly related, including the number of transactions made by each identity and time stamp of sending and receiving. Combining probability studies with optimization tools, we establish a model which allows us to determine, among all possible ways of linking between transactions and identities, the one that is most likely to be true. Subsequent transaction graph analysis could then be carried out, leading to the de-anonymization of the system. To solve the model, we provide exact algorithms based on mixed integer linear programming. Our research also establishes interesting relationships between the de-anonymization problem and other problems studied in the literature of theoretical computer science, e.g., the graph matching problem and scheduling problem.","PeriodicalId":248708,"journal":{"name":"Proceedings of the ACM Workshop on Blockchain, Cryptocurrencies and Contracts","volume":"146 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124886216","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Basic Properties of the Blockchain: (Invited Talk)","authors":"J. Garay","doi":"10.1145/3055518.3055519","DOIUrl":"https://doi.org/10.1145/3055518.3055519","url":null,"abstract":"As the first decentralized cryptocurrency, Bitcoin [1] has ignited much excitement, not only for its novel realization of a central bank-free financial instrument, but also as an alternative approach to classical distributed computing problems, such as reaching agreement distributedly in the presence of misbehaving parties, as well as to numerous other applications-contracts, reputation systems, name services, etc. The soundness and security of these applications, however, hinges on the thorough understanding of the fundamental properties of its underlying blockchain data structure, which parties (\"miners\") maintain and try to extend by generating \"proofs of work\" (POW, aka \"cryptographic puzzle\"). In this talk we follow the approach introduced in [2], formulating such fundamental properties of the blockchain, and then showing how applications such as consensus and a robust public transaction ledger can be built ``on top'' of them. The properties are as follows, assuming the adversary's hashing power (our analysis holds against arbitrary attacks) is strictly less than ½ and high network synchrony: Common prefix: The blockchains maintained by the honest parties possess a large common prefix. More specifically, if two honest parties \"prune\" (i.e., cut off) k blocks from the end of their local chains, the probability that the resulting pruned chains will not be mutual prefixes of each other drops exponentially in the that parameter. Chain quality: We show a bound on the ratio of blocks in the chain of any honest party contributed by malicious parties. In particular, as the adversary's hashing power approaches ½, we show that blockchains are only guaranteed to have few, but still some, blocks contributed by honest parties. Chain growth: We quantify the number of blocks that are added to the blockchain during any given number of rounds during the execution of the protocol. (N.B.: This property, which in [2] was proven and used directly in the form of a lemma, was explicitly introduced in [3]. Identifying it as a separate property enables modular proofs of applications' properties.) The above properties hold assuming that all parties-honest and adversarial-\"wake up\" and start computing at the same time, or, alternatively, that they compute on a common random string (the \"genesis\" block) only made available at the exact time when the protocol execution is to begin. In this talk we also consider the question of whether such a trusted setup/behavioral assumption is necessary, answering it in the negative by presenting a Bitcoin-like blockchain protocol that is provably secure without trusted setup, and, further, overcomes such lack in a scalable way-i.e., with running time independent of the number of parties [4]. A direct consequence of our construction above is that consensus can be solved directly by a blockchain protocol without trusted setup assuming an honest majority (in terms of computational power).","PeriodicalId":248708,"journal":{"name":"Proceedings of the ACM Workshop on Blockchain, Cryptocurrencies and Contracts","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124729918","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Rethinking Permissioned Blockchains","authors":"M. Vukolic","doi":"10.1145/3055518.3055526","DOIUrl":"https://doi.org/10.1145/3055518.3055526","url":null,"abstract":"Current blockchain platforms, especially the recent permissioned systems, have architectural limitations: smart contracts run sequentially, all node executes all smart contracts, consensus protocols are hard-coded, the trust model is static and not flexible, and non-determinism in smart-contract execution poses serious problems. Overcoming these limitations is critical for improving both functional properties of blockchains, such as confidentiality and consistency, as well as their non-functional properties, such as performance and scalability. We discuss these limitations in the context of permissioned blockchains, including an early version of the Hyperledger Fabric blockchain platform, and how a re-design of Hyperledger Fabric's architecture addresses them.","PeriodicalId":248708,"journal":{"name":"Proceedings of the ACM Workshop on Blockchain, Cryptocurrencies and Contracts","volume":"52 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127153034","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"DecReg: A Framework for Preventing Double-Financing using Blockchain Technology","authors":"Hidde Lycklama à Nijeholt, Joris Oudejans, Z. Erkin","doi":"10.1145/3055518.3055529","DOIUrl":"https://doi.org/10.1145/3055518.3055529","url":null,"abstract":"Factoring is an important financial instrument for SMEs to solve liquidity problems, where the invoice is cashed to avoid late buyer payments. Unfortunately, this business model is risky as it relies on human interaction and involved actors (factors in particular) suffer from information asymmetry. One of the risks involved is 'double-financing': the event that an SME extracts funds from multiple factors. To reduce this asymmetry and increase the scalability of this important instrument, we propose a framework, DecReg, based on blockchain technology. We provide the protocols designed for this framework and present performance analysis. This framework will be deployed in practice as of February 2017 in the Netherlands.","PeriodicalId":248708,"journal":{"name":"Proceedings of the ACM Workshop on Blockchain, Cryptocurrencies and Contracts","volume":"1B 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127723437","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Proceedings of the ACM Workshop on Blockchain, Cryptocurrencies and Contracts","authors":"S. Lokam, S. Ruj, K. Sakurai","doi":"10.1145/3055518","DOIUrl":"https://doi.org/10.1145/3055518","url":null,"abstract":"It is our pleasure to welcome you to The 1st ACM Workshop on Blockchain, Cryptocurrencies and Contracts (BCC'17) held in conjunction with The 12th ACM Asia Conference on Computer and Communications Security (AsiaCCS'17) during April 2-6, at Abu Dhabi, UAE. Blockchain is an emerging technology currently being used for a variety of applications such as cryptocurrencies and other financial transactions, smart properties, credential management, Internet-of-Things, supply chain management and many more. The theme of this workshop is to understand the foundations of blockchain technology and the design of new blockchain applications using smart contracts. \u0000 \u0000The call for papers attracted 17 submissions from Asia, Europe, and North America. The program committee accepted 5 papers based on their overall quality and novelty. Apart from the research papers, there are two keynote talks by Dr. Juan Garay and Dr. Marko Vukolic. We are grateful to the keynote speakers for accepting our invitations and to the authors of all the papers for submitting their work to this workshop. We thank the members of the program committee and external reviewers for their valuable service in evaluating the submissions. We hope these proceedings will serve as a valuable reference for researchers and practitioners in the field of blockchain technologies.","PeriodicalId":248708,"journal":{"name":"Proceedings of the ACM Workshop on Blockchain, Cryptocurrencies and Contracts","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132044372","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Towards Scalable and Private Industrial Blockchains","authors":"Wenting Li, Alessandro Sforzin, S. Fedorov, Ghassan O. Karame","doi":"10.1145/3055518.3055531","DOIUrl":"https://doi.org/10.1145/3055518.3055531","url":null,"abstract":"The blockchain emerges as an innovative tool that has the potential to positively impact the way we design a number of online applications today. In many ways, the blockchain technology is, however, still not mature enough to cater for industrial standards. Namely, existing Byzantine tolerant permission-based blockchain deployments can only scale to a limited number of nodes. These systems typically require that all transactions (and their order of execution) are publicly available to all nodes in the system, which comes at odds with common data sharing practices in the industry, and prevents a centralized regulator from overseeing the full blockchain system. In this paper, we propose a novel blockchain architecture devised specifically to meet industrial standards. Our proposal leverages the notion of satellite chains that can privately run different consensus protocols in parallel - thereby considerably boosting the scalability premises of the system. Our solution also accounts for a hands-off regulator that oversees the entire network, enforces specific policies by means of smart contracts, etc. We implemented our solution and integrated it with Hyperledger Fabric v0.6.","PeriodicalId":248708,"journal":{"name":"Proceedings of the ACM Workshop on Blockchain, Cryptocurrencies and Contracts","volume":"43 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132432302","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"SCPKI: A Smart Contract-based PKI and Identity System","authors":"Mustafa Al-Bassam","doi":"10.1145/3055518.3055530","DOIUrl":"https://doi.org/10.1145/3055518.3055530","url":null,"abstract":"The Public Key Infrastructure (PKI) in use today on the Internet to secure communications has several drawbacks arising from its centralised and non-transparent design. In the past there has been instances of certificate authorities publishing rogue certificates for targeted attacks, and this has been difficult to immediately detect as certificate authorities are not transparent about the certificates they issue. Furthermore, the centralised selection of trusted certificate authorities by operating system and browser vendors means that it is not practical to untrust certificate authorities that have issued rogue certificates, as this would disrupt the TLS process for many other hosts. SCPKI is an alternative PKI system based on a decentralised and transparent design using a web-of-trust model and a smart contract on the Ethereum blockchain, to make it easily possible for rogue certificates to be detected when they are published. The web-of-trust model is designed such that an entity or authority in the system can verify (or vouch for) fine-grained attributes of another entity's identity (such as company name or domain name), as an alternative to the centralised certificate authority identity verification model.","PeriodicalId":248708,"journal":{"name":"Proceedings of the ACM Workshop on Blockchain, Cryptocurrencies and Contracts","volume":"428 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115932097","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Enabling the Sharing Economy: Privacy Respecting Contract based on Public Blockchain","authors":"Lei Xu, Nolan Shah, Lin Chen, Nour Diallo, Zhimin Gao, Yang Lu, W. Shi","doi":"10.1145/3055518.3055527","DOIUrl":"https://doi.org/10.1145/3055518.3055527","url":null,"abstract":"Blockchain is a novel way to construct fully distributed systems and has the potential to disrupt many businesses including Uber and Airbnb within the sharing economy. Specifically, blockchain provides a method to enforce the agreement between a user and the physical property owner without using any trusted party, e.g., if a user pays the agreed money, the blockchain guarantees that he/she has access to the property. While a blockchain based system has many desirable features, it may leak privacy information of involved parties due to its openness to the public. To mitigate the privacy concern, we propose a privacy respecting approach for blockchain-based sharing economy applications, which leverages a zero-knowledge scheme. We also analyze the security features and performance of the proposed approach to demonstrate its effectiveness in these applications.","PeriodicalId":248708,"journal":{"name":"Proceedings of the ACM Workshop on Blockchain, Cryptocurrencies and Contracts","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122541653","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}