防止NTP广播模式下的时间同步
Preventing Time Synchronization in NTP's Broadcast Mode
摘要：
网络时间协议（NTP）是目前Internet上数以百万计的主机用来同步时钟的协议。时钟同步是许多网络应用程序正常运行所必需的。不同步的时钟可能会导致各种核心互联网服务的失败，包括DNS和基于RPKI的域间路由，并为更复杂的攻击打开通道。在本文中，我们描述了一种新的攻击，它可以防止配置在NTP的广播模式的客户端同步其时钟与服务器。我们在真实网络中进行了测试，并表明它是有效的认证和非认证的NTP广播/组播模式。我们还进行了实验，通过扫描整个IPv4地址空间来测量整体攻击面，并显示NTP广播模式正在被几个低层（高精度）主机使用。我们还提出了一些对策，以减轻拟议的攻击。
英文摘要：
Network Time Protocol (NTP) is used by millions of hosts in Internet today to synchronize their clocks. Clock synchronization is necessary for many network applications to function correctly. Unsynchronized clock may lead to failure of various core Internet services including DNS and RPKI based interdomain routing and opens path for more sophisticated attacks. In this paper, we describe a new attack which can prevent a client configured in NTP's broadcast mode from synchronizing its clock with the server. We test the attack in real networks and show that it is effective in both authenticated and unauthenticated broadcast/multicast modes of NTP. We also perform experiments to measure the overall attack surface by scanning the entire IPv4 address space and show that NTP broadcast mode is being used in the wild by several low stratum (highly accurate) hosts. We also suggest few countermeasures to mitigate the proposed attack.
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