Researchers from Warsaw University of Technology have found a new way to hide secret messages in internet traffic by manipulating the back-and-forth sequence and messages exchanged each time an internet packet is sent.
What is RSTEG?
RSTEG (Retransmission Steganography) is a network application of steganography, which is the science of hiding messages in documents. The methods are based on the fact that after an internet packet is received successfully the computer sends a confirmation. RSTEG deliberately withholds the acknowledgment, which then prompts the packet to be resent.
“In the context of RSTEG, a sender replaces original payload with a steganogram instead of sending the same packet again,” the paper, authored by Wojciech Mazurczyk, Miłosz Smolarczyk, and Krzysztof Szczypiorski, states. “When the re-transmitted packet reaches the receiver, he/she can then extract hidden information.”
RSTEG works only with TCP, but the principle can be applied to other protocols as well, including those for wireless networks. Read more about RSTEG in this PDF paper.