| Summary: | 碩士 === 國立臺灣科技大學 === 資訊工程系 === 103 === The clock skew, or the physical ticking rate of the clock, of a device is potential to serve as the fingerprint in identification/authentication purpose. However, it remains an open issue on detecting clock skew replication attacks realized by sending fake timestamps. In this research, it is confirmed that an attacker may fake any target skew with errors in the range of ±1ppm. On the other hand, it is also observed that the values of fake timestamps are affected by the resolution of the system time clock. When the resolution is 1ms or lower, there exists regularly the so-called jump points between consecutive offsets. The scale of each jump is theoretically the very resolution of the system clock. We utilized this characteristic to develop a filtering method on the detection of fake timestamps. When regular jumps are detected, the filter module would abandon the scale of jumps to recover the origin clock skews. Experiment results on 15.6ms and 1ms time resolutions have shown that the developed method is effective on detecting replication attacks, and the recovered clock skews are no more than 1ppm away from the real skews of attackers’ devices.
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