Networking, consensus, and security of blockchain applications

区块链技术还远未成熟。我们的提案侧重于需要进一步发展的三个关键领域：基于分布式区块链的分类账的网络性能优化、共识机制以及存储在区块链中的数据的安全性和隐私性。我们将研究网络特征对系统性能的影响，特别是对块传播和确认时间，分叉概率和分类账不一致时间的影响。我们将设计、开发和评估先进的机制、协议和消息格式，以限制分叉等不一致性的可能性，并减少带宽使用。拟议的变化将有助于提高账本数据的一致性、处理速度和准确性，从而减少基于区块链的系统的攻击面。我们计划专注于限制延迟并保证最终性的混合共识方法，就像PBFT（实用拜占庭容错）等集中式共识算法一样，但也提供了分布式，无许可环境中的简单性和易用性，就像比特币中使用的Nakamoto共识一样。我们将开发创新的机制，以实现这两个有点冲突的要求之间的最佳权衡，使用灵活的成员和旋转的共识领导者的分布式范例。最后，我们将研究区块链技术的使用，为安全和隐私至关重要的垂直行业开发尖端应用程序，特别是在物联网（IoT）和电子医疗系统中。物联网系统构成了一个挑战，因为大量的设备具有有限的计算和通信能力，无法维护完整的区块链。因此，区块链将用于物联网设备和物联网网关的相互认证，或者更有可能用于边缘或云服务器，并有助于数据聚合和后续验证。 由于用户数量庞大，个人需要控制对其医疗数据的访问，医疗保健系统面临着巨大的挑战。我们设想区块链技术将用于支持基本的安全功能，但由于其规模，不会收集或存储实际数据。相反，区块链将保存用户身份验证信息，数据所有者的访问授权以及（可能）这些授权的后续验证，并且（最重要的是）它将记录有关必须根据访问时有效的授权执行的每个数据访问的信息。我们还将研究分片技术，该技术允许用户在本地存储中仅维护全局区块链的一部分，以便于访问，同时保持与全局区块链的同步。

Blockchain technology is still far from maturity. Our proposal focuses on three crucial areas in need of further development: network performance optimization for distributed blockchain-based ledgers, consensus mechanisms, and security and privacy of data stored in the blockchain. We will investigate the impact of network characteristics on system performance, in particular on block propagation and confirmation time, probability of forking, and ledger inconsistency time. We will devise, develop, and evaluate advanced mechanisms, protocols, and message formats that will restrict the potential for inconsistencies such as forking and reduce bandwidth usage. The proposed changes will contribute to increased consistency, processing rate, and accuracy of ledger data and, thus, reduce the attack surface of blockchain-based systems. We plan to focus on hybrid consensus approaches that limit latency and guarantee finality, as is the case with centralized consensus algorithms such as PBFT (Practical Byzantine Fault Tolerance) but also offer the simplicity and ease of use in a distributed, permissionless environment, as is the case with the Nakamoto consensus used in Bitcoin. We will develop innovative mechanisms to achieve the best tradeoff between the two somewhat conflicting requirements, using the distributed paradigm with flexible membership and a rotating consensus leader. Finally, we will investigate the use of blockchain technology to develop cutting edge applications for vertical industries where security and privacy is of paramount importance, in particular in Internet of Things (IoT) and e-healthcare systems. IoT systems pose a challenge due to the large number of devices with restricted computational and communication capabilities that cannot maintain a full blown blockchain. Thus blockchain will be used for mutual authentication of IoT devices and IoT gateways or, more likely, edge or cloud servers, and also to assist in data aggregation and subsequent verification.  Healthcare systems pose a big challenge on account of the large number of users and the need for individuals to control access to their healthcare data. We envisage that blockchain technology will be used to support basic security functions but not collect or store actual data due to its size. Instead, blockchain will hold user authentication information, access authorizations by data owners and (possibly) subsequent revocations of those authorizations, and (most importantly) it will record information about each and every data access that must be executed in accordance with the authorization valid at the moment of access. We will also look into sharding techniques that allow users to maintain only a portion of the global blockchain in their local storage for easy access whilst maintaining synchronism with the global blockchain.