在Tezos权益证明中防御恶意Reorg
Defending Against Malicious Reorgs in Tezos Proof-of-Stake
摘要：
区块链的目的是不可变的，因此能够通过链重组（恶意重组）删除交易的攻击者可以执行有利可图的双重花费攻击。我们研究了攻击者可以在Tezos权益证明协议中执行reorgs的速率。例如，具有40%的抵押权的攻击者能够以平均每天一次的速度执行20个块的恶意重组，并且随着抵押权增长超过40%，攻击概率超线性地增加。此外，Tezos协议的攻击者提前知道何时会出现攻击机会，并可以使用此知识来安排交易以进行双重花费。我们表明，在特定情况下，Tezos协议可以进行调整，以防止深度reorgs。例如，我们证明了协议参数，减少了两个数量级的长度为20重组机会的40%的攻击者。我们还观察到优化深度重新组织的鲁棒性（可能是净利润的昂贵偏差，因为它们可以实现双重支出）和自私挖掘的鲁棒性（即使没有双重支出，通常也会导致短期重新组织的挖掘偏差）之间的权衡。也就是说，能够最好地抵御一种攻击的参数会使另一种攻击变得容易。最后，我们开发了一种方法，仅使用公开可用的信息来监控Tezos区块链的健康状况。
英文摘要：
Blockchains are intended to be immutable, so an attacker who is able to delete transactions through a chain reorganization (a malicious reorg) can perform a profitable double-spend attack. We study the rate at which an attacker can execute reorgs in the Tezos Proof-of-Stake protocol. As an example, an attacker with 40% of the staking power is able to execute a 20-block malicious reorg at an average rate of once per day, and the attack probability increases super-linearly as the staking power grows beyond 40%. Moreover, an attacker of the Tezos protocol knows in advance when an attack opportunity will arise, and can use this knowledge to arrange transactions to double-spend. We show that in particular cases, the Tezos protocol can be adjusted to protect against deep reorgs. For instance, we demonstrate protocol parameters that reduce the rate of length-20 reorg opportunities for a 40% attacker by two orders of magnitude. We also observe a trade-off between optimizing for robustness to deep reorgs (costly deviations that may be net profitable because they enable double-spends) and robustness to selfish mining (mining deviations that result in typically short reorgs that are profitable even without double-spends). That is, the parameters that optimally protect against one make the other attack easy. Finally, we develop a method that monitors the Tezos blockchain health with respect to malicious reorgs using only publicly available information.
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