A Preliminary Study on the Creation of a Covert Channel with HTTP Headers

Steganography conceals confidential information within seemingly innocuous data and has evolved with technological advancements. In network steganography, data is hidden in packets exchanged at different levels (e.g., Ethernet, IP, TCP, etc.). This paper considers the HTTP protocol for setting up a covert channel between two endpoints: the main motivation is that creating ad-hoc HTTP packet headers does not require superuser privileges, while TCP segment headers, for example, require them. This simplifies the execution of tools implementing the channel. Moreover, HTTP/HTTPS traffic is usually allowed to flow to/from a local network and is often not modified (if not automatically proxied). Therefore, we propose a detailed exploration of a covert channel protocol by modulating standard fields in the HTTP headers for unidirectional communication, i.e., from a sender to a receiver.