Hybrid Covert Channel an Obliterate for Information Hiding

Abstract

In a prisoners’ problem there are two individuals attempt to communicate covertly without alerting a “warden” who controls the communications channel. This problem becomes more or less difficult because of various assumptions or requirements. One assumption which makes the problem considerably more manageable is that the participants are allowed to share some secret information such as an encryption key prior to imprisonment. Another assumption, which makes the problem much more difficult, is that the warden be allowed to modify as well as read the messages sent between the prisoners. This paper describes Hybrid Covert Channel techniques, in which no secret information needs to be shared before imprisonment. In this case if the warden is not allowed to modify the contents of the channel, a modification of an existing protocol will be shown to admit pure steganography. Then, a technique is described that allows pure steganography between two prisoners in the presence of an active content-modifying warden. This technique is possible through the use of two distinct channels rather than one: the subliminal channel for steganographic communication which is augmented by a supraliminal channel, one in which information is not hidden from the warden but cannot be modified.