To implement a blockchain, we need a blockchain protocol for all the nodes to follow. To design a blockchain protocol, we need a block publisher selection mechanism and a chain selection rule. In Proof-of-Stake (PoS) based blockchain protocols, block publisher selection mechanism selects the node to publish the next block based on the relative stake held by the node. However, PoS protocols, such as Ouroboros v1, may face vulnerability to fully adaptive corruptions. In this paper, we propose a novel PoS-based blockchain protocol, QuickSync, to achieve security against fully adaptive corruptions while improving on performance. We propose a metric called block power, a value defined for each block, derived from the output of the verifiable random function based on the digital signature of the block publisher. With this metric, we compute chain power, the sum of block powers of all the blocks comprising the chain, for all the valid chains. These metrics are a function of the block publisher's stake to enable the PoS aspect of the protocol. The chain selection rule selects the chain with the highest chain power as the one to extend. This chain selection rule hence determines the selected block publisher of the previous block. When we use metrics to define the chain selection rule, it may lead to vulnerabilities against Sybil attacks. QuickSync uses a Sybil attack resistant function implemented using histogram matching. We prove that QuickSync satisfies common prefix, chain growth, and chain quality properties and hence it is secure. We also show that it is resilient to different types of adversarial attack strategies. Our analysis demonstrates that QuickSync performs better than Bitcoin by an order of magnitude on both transactions per second and time to finality, and better than Ouroboros v1 by a factor of three on time to finality.

翻译：为实现区块链，需要所有节点遵循的区块链协议；设计协议时需包含区块发布者选择机制与链选择规则。在基于权益证明（PoS）的区块链协议中，区块发布者选择机制根据节点持有的相对权益来挑选下一区块的发布节点。然而，诸如Ouroboros v1等PoS协议可能面临完全自适应腐败攻击的脆弱性。本文提出一种新型PoS区块链协议QuickSync，在提升性能的同时抵御完全自适应腐败攻击。我们定义区块能量（block power）作为每个区块的度量值，该值基于区块发布者数字签名的可验证随机函数输出计算得出。通过该度量计算所有有效链的链能量（chain power），即链中所有区块能量之和。这些度量是区块发布者权益的函数，以实现协议的PoS特性。链选择规则选取链能量最高的链作为扩展对象，从而确定上一区块的选定发布者。当使用度量定义链选择规则时，可能引发针对女巫攻击的脆弱性。QuickSync采用基于直方图匹配的抗女巫攻击函数实现。我们证明了QuickSync满足公共前缀、链增长与链质量属性，因此具有安全性；同时证明其对多种敌对攻击策略具有弹性。分析表明，QuickSync在每秒交易数与最终确认时间方面均比比特币高出一个数量级，且最终确认时间比Ouroboros v1快三倍。