Aniello Castiglione Alfredo De Santis Ugo Fiore Francesco Palmieri E-mail-Based Covert Channels for Asynchronous Message Steganography. 503-508 2011 IMIS http://dx.doi.org/10.1109/IMIS.2011.133 conf/imis/2011 db/conf/imis/imis2011.html#CastiglioneSFP11