Covert Channels in Computer Networks

The idea behind covert channels is to hide 'illegitimate' communication channels in 'legitimate' communication channels so that any observer is unaware of the hidden communication.The problem was first published by Lampson in 1973. He defined covert channels as "channels, [...] not intended for information transfer at all". In 1985 the US DoD defined the concept of covert channels as follows: "A covert channel is any communication channel that can be exploited by a process to transfer information in a manner that violates the system'ssecurity policy". 

Covert channels in general have been the topic of research for over three decades. More recently covert channels have been researched in computer network protocols. The idea was initially proposed by Girling in 1987 and illustrated with some examples. Some research was done during the 90's but there are only few publications. Only recently (since 2002) this topic seemed to have sparked significant interest in the networking and security research community.

Covert channels are part of the wider area of information hiding. A closely related topic is steganography (meaning covered writing in greek), which is the hiding of information in audio, pictures and video. Hence some people also refer to covert channels in network protocols as protocol or Internet steganography.

Subliminal channels proposed by Simmons in 1983 are covert channels embedded in digital signatures.

This web page focusses on covert channels in computer network protocols but also contains some information about subliminal channels, covert channels in general, steganography etc. I started this page when I did the literature survey for my PhD. Many thanks to a number of people who contributed by sending me additional references!

Publications on Covert Channels in Computer Network Protocols

Publications on Subliminal Channels

More general publications on Covert Channels

Covert Channels in Computer Networks Tools

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