This document specifies an extension to the NTPv4 client, named Khronos, which is used as a “watchdog” alongside NTPv4, and provides improved security against time shifting attacks. Khronos involves changes to the NTP client’s system process only. Since it does not affect the wire protocol, the Khronos mechanism is applicable to any current or future time protocol.
We present Chronos, a new NTP client that achieves good synchronization even in the presence of powerful attackers who are in direct control of a large number of NTP servers. Importantly, Chronos is backwards compatible with legacy NTP and involves no changes whatsoever to NTP servers.