[论文解读] Hijacking Bitcoin: Routing Attacks on Cryptocurrencies

Maria Apostolaki, Aviv Zohar+1 more|arXiv (Cornell University)|May 24, 2016

Blockchain Technology Applications and Security参考文献 28被引用 9

一句话总结

本文表明，通过BGP劫持和中间人干扰，比特币易受路由攻击，攻击者仅需操纵不足100个BGP前缀即可隔离矿池或延迟区块传播。研究显示，此类攻击可使50%的算力中断，区块传播延迟最高达20分钟，且通过真实世界的路由和比特币拓扑数据验证了其实际可行性。

ABSTRACT

As the most successful cryptocurrency to date, Bitcoin constitutes a target of choice for attackers. While many attack vectors have already been uncovered, one important vector has been left out though: attacking the currency via the Internet routing infrastructure itself. Indeed, by manipulating routing advertisements (BGP hijacks) or by naturally intercepting traffic, Autonomous Systems (ASes) can intercept and manipulate a large fraction of Bitcoin traffic. This paper presents the first taxonomy of routing attacks and their impact on Bitcoin, considering both small-scale attacks, targeting individual nodes, and large-scale attacks, targeting the network as a whole. While challenging, we show that two key properties make routing attacks practical: (i) the efficiency of routing manipulation; and (ii) the significant centralization of Bitcoin in terms of mining and routing. Specifically, we find that any network attacker can hijack few (<100) BGP prefixes to isolate ~50% of the mining power---even when considering that mining pools are heavily multi-homed. We also show that on-path network attackers can considerably slow down block propagation by interfering with few key Bitcoin messages. We demonstrate the feasibility of each attack against the deployed Bitcoin software. We also quantify their effectiveness on the current Bitcoin topology using data collected from a Bitcoin supernode combined with BGP routing data. The potential damage to Bitcoin is worrying. By isolating parts of the network or delaying block propagation, attackers can cause a significant amount of mining power to be wasted, leading to revenue losses and enabling a wide range of exploits such as double spending. To prevent such effects in practice, we provide both short and long-term countermeasures, some of which can be deployed immediately.

研究动机与目标

• 分析针对比特币对等网络基础设施的路由级别攻击的可行性和影响。
• 研究自治系统（AS）级别的对手如何利用路由集中化来分割比特币节点或延迟区块传播。
• 使用实时BGP和比特币全节点数据，量化此类攻击在现实世界中的有效性。
• 提出实用的短期和长期缓解对策，以减轻这些威胁。
• 证明即使小规模的路由操纵，由于比特币的路由和挖矿集中化，也能导致显著的网络中断。

提出的方法

• 构建了针对比特币的路由攻击分类法，区分了分区攻击与延迟攻击。
• 收集了真实世界的BGP路由数据和比特币全节点流量，以映射网络拓扑并识别易受攻击的自治系统（AS）。
• 通过模拟BGP前缀劫持，隔离目标比特币节点，并测量其对网络分区的影响。
• 通过修改关键比特币消息（如区块传播）实施中间人干扰，延迟消息传输，而无需更改消息内容。
• 使用UDP心跳和多连接区块请求，评估比特币客户端对部分拦截的弹性。
• 提出并评估了包括随机端口、加密控制通道和心跳机制在内的缓解对策，以检测和防止操纵。

实验结果

研究问题

• RQ1 AS级别的对手在多大程度上可通过BGP劫持分割比特币网络？
• RQ2 需要多少个BGP前缀才能隔离比特币挖矿算力的显著比例？
• RQ3 中间人攻击者能否在不被察觉的情况下延迟区块传播，延迟程度如何？
• RQ4 挖矿池和路由基础设施的集中化如何放大路由攻击的影响？
• RQ5 有哪些可立即部署的实用缓解对策可降低此类攻击的风险？

主要发现

• 攻击者仅需劫持少于100个BGP前缀，即可隔离约50%的比特币挖矿算力，即使在多宿主矿池的情况下也成立。
• 中间人攻击者可通过选择性修改少量关键比特币消息，将区块传播延迟最高达20分钟。
• 该攻击在实践中可行，已通过比特币全节点和BGP路由表的真实数据得到验证。
• 比特币依赖默认端口8333且缺乏加密控制通道，使其极易遭受流量识别和拦截。
• 比特币节点和挖矿池在自治系统（AS）层面的集中化显著增加了基于路由的攻击面。
• 可部署的缓解对策，如随机端口、UDP心跳和多连接区块请求，能有效降低未被察觉的操纵风险。