Covert Channels through External Interference

This paper introduces interference channels, a new kind of covert channel that works by creating external interference on a shared communications medium (such as a wireless network). Unlike previous covert channels, here the covert sender does not need to compromise an authorized sender or require the ability to send messages on the network, but only needs the ability to jam traffic for short intervals. We describe an implementation of a wireless interference channel for 802.11 networks that can be used to superimpose low bandwidth messages over data streams, even when the network is encrypted or has other access controls. This channel is particularly well suited to watermarking VoIP flows, without compromising any routers or endpoint hosts.