Covert storage caches using the NTP protocol

Abstract

Recently, new methods were discovered to secretly store information in network protocol caches by exploiting functionalities of ARP and SNMP. Such a covert storage cache is referred to as a "Dead Drop". In our present research, we demonstrate that hidden information can also be stored on systems with an active NTP service. We present one method based upon ephemeral associations and one method based upon the most recently used (MRU) list and measure their storage duration and capacity. Our approach improves over the previous approach with ARP as it allows to transport hidden information across the internet and thus outside of local area networks. The preliminary results for both Dead Drops indicate that more than 100 entries with secret data can persist for several hours. Finally, we discuss the detectability and countermeasures of the proposed methods as well as their limitations.