A covert channel is a type of communication method which allows for the transfer of data by exploiting resources that are commonly available on a computer system. Covert channels are types of communication that are invisible to the eyes of the system administrators or other authorized users. Covert channels are within a computer or network system, but are not legitimate or sanctioned forms of communication. They may be used to transfer data in a clandestine fashion.
Examples of covert channels include:
Embedding data in the headers of packets - The covert data is embedded in the headers of normal packets and sent over a protocol related to the normal activities of the computer system in question.
Data piggybacked on applications - Malicious applications are piggybacked with legitimate applications used on the computer system, sending confidential data.
Time-based channel - The timing of certain actions or transmissions is used to encode data.
Covert storage channel - Data is stored within a computer system on disk or in memory and is hidden from the system's administrators.
Data diddling - This involves manipulating data to contain malicious code or messages.
Steganography - This is a process of hiding messages within other types of media such as images and audio files.
Covert channels are commonly used for malicious purposes, such as the transmission of sensitive data or the execution of malicious code on a computer system. They can also be used for legitimate purposes, however, such as creating an encrypted communication channel.