Got a secret message to send? Say it with silence. A new technique can embed secret data during a phone call on Skype. “There are concerns that Skype calls can be intercepted and analysed,” says Wojciech Mazurczyk at the Institute of Telecommunications in Warsaw, Poland. So his team’s SkypeHide system lets users hide extra, non-chat messages during a call.
Mazurczyk and his colleagues Maciej Kara? and Krysztof Szczypiorski analysed Skype data traffic during calls and discovered an opportunity in the way Skype “transmits” silence. Rather than send no data between spoken words, Skype sends 70-bit-long data packets instead of the 130-bit ones that carry speech.