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Due to the widespread adoption of the internet and its services, protocols have been established and new ones arise every year. Either for securing connections, ciphering information or service authentication, protocols place an important part in network communications. The TCP/IP has become one of the ubiquitous protocol suites for secure communication, and therefore, a desirable target for covert information encapsulation. In this article, we will discuss the art of unauthorized data transfer - covert techniques - for data encapsulation in protocol data packets, emphasizing headers fields manipulation.