  Covert channel techniques are used by attackers to transfer data in a way
prohibited by the security policy. There are two main categories of covert
channels: timing channels and storage channels. This paper introduces a new
storage channel technique called a protocol channel. A protocol channel
switches one of at least two protocols to send a bit combination to a
destination. The main goal of a protocol channel is that packets containing
covert information look equal to all other packets within a network, what makes
a protocol channel hard to detect.
