Covert Channel

The covert channel got it’s name because it is concealed within the medium of a genuine communications medium. They generally manipulate specific areas of the medium in an unexpected way in order to transmit data without being detected. While covert channels absorb unauthorized bandwidth from legitimate channels, that bandwidth often goes unused anyway, allowing the covert channel to remain concealed. For instance, steganography uses low-order bits of data for each pixel of an image to transmit information for the covert channel, while other bits carry the genuine message. This may result in a slight change of the image but is likely to go unnoticed. While completely eliminating covert channels is almost impossible, they can be drastically reduced by design. This can be done by using characteristics of a communications medium that is uncontrolled by a legitimate user. Since it is very unlikely that users will search for patterns of file tampering, the channel can remain undetected for a long period of time and limit the possibility of being victimized.