Covert Channel - Data Hiding in OSI Model

Data Hiding in OSI Model

As Handel and Sanford take a broader perspective and focus on covert channels within the general design of network communication protocols. They employ the OSI model as a basis for their development in which they characterize system elements having potential to be used for data hiding. The adopted approach has advantages over these are because standards opposed to specific network environments or architectures are considered. Foolproof steganographic schemes are not devised.

Rather, basic principles for data hiding in each of seven OSI layers are established. Besides suggesting the use of the reserved fields of protocols headers (that are easily detectable) at higher network layers, Handel and Sanford also propose the possibility of timing channels involving CSMA/CD manipulation at the physical layer.

The work by them identifies covert channel merit such as:

• Detectability: Covert channel must be measurable by the intended recipient only.
• Indistinguishability: Covert channel must lack identification.
• Bandwidth: number of data hiding bits per channel use.

The covert channel analysis presented here, however does not consider issue such as interoperability of these data hiding techniques with other network nodes, covert channel capacity estimation, effect of data hiding on the network in terms of complexity and compatibility. Moreover, the generality of the techniques cannot be fully justified in practice since the OSI model does not exist per se in functional systems.