Survey on Network-based Covert Communication Techniques

Covert communications is the act of transmitting messages in a hidden or disguised manner. They have been utilized throughout history for a variety of purposes, ranging from espionage to personal privacy. Covert communication channels are intra-system channels that allow for the transmission of data without other parties knowing of their existence. The key concept is to hide the communication channel itself. Most channels leverage components of network protocols to increase the capacity of secret information sent. However, advanced monitoring and machine learning-based detection have made it increasingly difficult to conceal data. This means that to successfully set up covert communication channels, the sender and receiver have to be creative about how they encode and decode secret data. Many researchers have developed different covert channel schemes based on timing and storage techniques leveraging network protocols. This paper aims to investigate all recent network covert communication schemes in accordance with criteria and scrutinize their weaknesses and detection methods. We find that a storage-based approach with custom encoding and leveraging recommended protocol produces the best results when designing a covert channel scheme.