Covert channels in network protocols are a technique aiming to hide the very existence of secret communication in computer networks. In this work we present a systematic in-depth analysis of covert channels by modification for the Network Time Protocol (NTP). Our analysis results in the identification of 49 covert channels, by applying a covert channel pattern-based taxonomy. The summary and comparison based on nine selected key attributes show that NTP is a plausible carrier for covert channels. The analysis results are evaluated in regards to common behavior of NTP implementations in six major operating systems. Two channels are selected and implemented to be evaluated in network test-beds. By hiding encrypted high entropy data in a high entropy field of NTP we show in our first assessment that practically undetectable channels can be implemented in NTP, motivating the required further research.
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Hielscher et al. (2021) studied this question.
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