区块链用户匿名与可追踪技术

区块链具有透明性、数据完整性、防篡改等优点,在金融、政府、军事等领域有重要应用价值。目前有越来越多的工作研究区块链的隐私保护问题,典型的包括门罗币、Zerocash, Mixcoin等等。这些隐私保护方法可以用于保护区块链上用户的身份和交易的金额。隐私保护方案是双刃剑,一方面是对合法用户隐私的完善保护,另一方面如果完全脱离监管,则是对洗钱、勒索等违法犯罪行为的姑息和纵容。针对区块链上各种层出不穷的隐私保护方案,监管也要与时俱进。该文研究区块链用户身份的隐私保护和监管方法,提出了用户匿名和可追踪的技术,旨在推动区块链在实际中的应用。     

区块链技术在信息技术安全与隐私保护中的应用

随着网络和移动设备用户数量的增长,信息安全和隐私保护变得越来越重要。文中提出了一种基于区块链的解决方案,即隐私保护型区块链系统,以保护用户数据的安全性和隐私性。此外,设计并实施了一种利用区块链不可篡改性和分布式特性的系统,以确保数据的完整性和防止未经授权的访问。通过仿真实验,验证了该系统的有效性和效率。实验结果表明,该系统在提高用户数据安全性和隐私性方面表现优异,是一种值得推广的新型数据保护策略。     

一种完全匿名和公平高效的拍卖协议

为了保护电子拍卖过程中投标者的隐私,以及防止投标者中标后反悔,本文从利用签名技术和位承诺协议, 提出了一个安全有效的匿名拍卖协议。该协议不仅保证了标价的保密性和可验证性,投标者对所投标价的不可否认 性和匿名性,而且保证了在整个拍卖过程中,无人可以操纵其他人的投标。即使某一投标者与拍卖代理相互勾结, 也不会影响协议的安全性和有效性。更为重要的是,该协议遵循第二价位原理,从而使商品分配达到最优。与先前 的工作相比,该协议具有更好的扩展性和效率,适合于分布式的网上拍卖。     

Attribute-Based Worker Selection Scheme by Using Blockchain in Decentralized Crowdsourcing Scenario

Traditional crowdsourcing based on cen-tralized management platform is vulnerable to Distributed denial of service (DDoS) attack and single point of failure. Combining blockchain technology with crowdsourcing can well solve the above problems, enabling users to realize peer-to-peer transactions and collaboration based on decentralized trust in distributed systems where nodes do not need to trust each other. Although the current methods have solved the above problems, task publishers select workers based on their reputation values, which has two disadvantages: subjectivity and difficulty in initial value setting. Due to the complexity of crowdsourcing network, there will be malicious users in the network. The requirement for anonymity protects both legitimate and malicious users. In order to solve these problems, we propose an attribute-based worker selection scheme using the private set intersection technology. Our scheme also realizes the malicious user identity disclosure function. A concrete example of our scheme is given.     

基于联邦学习的本地化差分隐私机制研究

联邦学习与群体学习作为当前热门的分布式机器学习范式,前者能够保护用户数据不被第三方获得的前提下在服务器中实现模型参数共享计算,后者在无中心服务器的前提下利用区块链技术实现所有用户同等地聚合模型参数。但是,通过分析模型训练后的参数,如深度神经网络训练的权值,仍然可能泄露用户的隐私信息。目前,在联邦学习下运用本地化差分隐私(LDP)保护模型参数的方法层出不穷,但皆难以在较小的隐私预算和用户数量下缩小模型测试精度差。针对此问题,该文提出正负分段机制(PNPM),在聚合前对本地模型参数进行扰动。首先,证明了该机制满足严格的差分隐私定义,保证了算法的隐私性;其次分析了该机制能够在较少的用户数量下保证模型的精度,保证了机制的有效性;最后,在3种主流图像分类数据集上与其他最先进的方法在模型准确性、隐私保护方面进行了比较,表现出了较好的性能。     

Smart contract applications within blockchain technology: A systematic mapping study

With the advent of blockchain, smart contracts have become one of the most sought-after technologies because of the high customisability they add to transactions. This has given rise to many smart contract applications in areas ranging from financial services, life sciences and healthcare to energy resources and voting. However, due to their infancy, smart contracts still pose many challenges that encumber the stakeholders who interact with them: users, developers and the organisations that are built on top of smart contracts. This study aims to contribute to the body of knowledge of smart contracts within blockchain technology. Based on a systematic mapping study, we offer a broad perspective on their problems and corresponding solutions, present the research trends within the area and compile the 64 papers identified, grouped by top publication sources, channels, methods and approaches. We conclude that, since 2016, there has been an increasing trend towards the publication of blockchain-based smart contract articles at conferences and journals, mainly reflecting experiments and presenting methods, tools and models. According to the results, the most commonly discussed problems and solutions in the literature are related to the security, privacy and scalability of blockchain and the programmability of smart contracts.     

基于无证书的多方合同签署协议

线上合同签署在电子商务中日益普及,在互不信任的签署方之间签署一份合同并不是一件简单的事情,各方就合同签署问题提出过许多合同签署协议。其中较多的协议是带有第三方参与的,但是在效率方面并不占优势,且易出现安全问题。现有借助区块链技术取代第三方参与的合同签署协议中,区块链的公开验证对不管是签署方还是待签署合同的敏感信息又发起了挑战。且大多协议针对于双方合同签署,随着签署方数量的增加,协议的通信成本和复杂度都在急剧增加。该文结合现有协议,提出一个高效的多方合同签署协议,协议中通过基于无证书的高效聚合签名方案,用于提高区块链下签署方签名验证效率,在区块链上仅公开签署方的临时密钥以减少系统开销。该协议满足正确性、安全性、公平性、私密性以及高效性。     

Defense against misbehavior in anonymous vehicular ad hoc networks

Vehicular ad hoc network (VANET) can offer various services and benefits to VANET users and thus deserves deployment effort. Misusing such network could cause destructive consequences. It is therefore necessary to discourage misbehavior and defend VANET systems against it, in order to ensure correct and smooth operations of the network. In this paper, we review the techniques for handling misbehavior in VANETs, particularly where anonymous communications are desired to conserve user privacy since it adds more complexity to the defense against misbehavior. A new scheme is proposed to punish misbehaving users and can be employed in both inter-vehicle and vehicle-to-infrastructure anonymous communications. Our scheme leverages some threshold authentication technique that dynamically revokes a user’s credential, while providing the flexibility of whether to reveal the user’s identity and tolerating unintentional misbehavior such as hardware malfunctioning.     

区块链隐私众包中的数据验证与可控匿名方案

针对隐私众包场景下出现的数据验证、匿名作恶检测和跨平台资源交互等需求,该文基于区块链技术,并结合零知识证明与环签名技术,提出一种联盟链架构下的隐私众包方案。该方案依靠零知识证明实现对加密数据的验证,依靠链接可撤销环签名改进方案实现工人身份的可控匿名,引入联盟链架构实现众包实体之间的资源交互。在完成众包完整流程的同时,实现隐私众包所需的数据保护与身份保护。安全性分析表明,该方案具有隐私性、可验证性、可控匿名性与公平性。实验结果验证了方案在效率与性能方面的有效性。     

区块链技术在数字身份验证中的可行性研究

文中探讨了区块链技术在数字身份验证中的应用及其可行性。随着数字化进程的加速,传统的身份验证机制面临着日益严峻的挑战,包括数据安全、隐私保护、用户体验等。区块链技术以其独特的去中心化特性、不可篡改的数据记录以及高度的透明性和安全性,为解决这些问题提供了新的途径。     

Ring Signatures: Stronger Definitions, and Constructions without Random Oracles

Ring signatures, first introduced by Rivest, Shamir, and Tauman, enable a user to sign a message so that a ring of possible signers (of which the user is a member) is identified, without revealing exactly which member of that ring actually generated the signature. In contrast to group signatures, ring signatures are completely “ad-hoc” and do not require any central authority or coordination among the various users (indeed, users do not even need to be aware of each other); furthermore, ring signature schemes grant users fine-grained control over the level of anonymity associated with any particular signature. This paper has two main areas of focus. First, we examine previous definitions of security for ring signature schemes and suggest that most of these prior definitions are too weak, in the sense that they do not take into account certain realistic attacks. We propose new definitions of anonymity and unforgeability which address these threats, and give separation results proving that our new notions are strictly stronger than previous ones. Second, we show the first constructions of ring signature schemes in the standard model. One scheme is based on generic assumptions and satisfies our strongest definitions of security. Two additional schemes are more efficient, but achieve weaker security guarantees and more limited functionality. An extended abstract of this paper appeared in the 3rd Theory of Cryptography Conference, March 4–7 2006, New York, NY, USA (Lecture Notes in Computer Science, vol. 3876, pp. 60–79, 2006). Supported in part by NSF Trusted Computing Grants #0310499 and #0310751, NSF-ITR #0426683, and NSF CAREER award #0447075. Supported by NSF Trusted Computing Grant #0310499 and NSF-ITR #0426683.