  This paper presents a new steganographic method called WiPad (Wireless
Padding). It is based on the insertion of hidden data into the padding of
frames at the physical layer of WLANs (Wireless Local Area Networks). A
performance analysis based on a Markov model, previously introduced and
validated by the authors in [10], is provided for the method in relation to the
IEEE 802.11 a/g standards. Its results prove that maximum steganographic
bandwidth for WiPad is as high as 1.1 Mbit/s for data frames and 0.44 Mbit/s
for acknowledgment (ACK) frames. To the authors' best knowledge this is the
most capacious of all the known steganographic network channels.
