Got a secret message to send? Say it with silence. A new technique can embed secret data during a phone call on Skype. 鈥淭here are concerns that Skype calls can be ,鈥� says Wojciech Mazurczyk at the Institute of Telecommunications in Warsaw, Poland. So his team鈥檚 SkypeHide system lets users hide extra, non-chat messages during a call.
Mazurczyk and his colleagues Maciej Kara艣 and Krzysztof Szczypiorski analysed Skype data traffic during calls and discovered an opportunity in the way Skype 鈥渢ransmits鈥� 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.
The team hijacks these silence packets, injecting encrypted message data into some of them. The Skype receiver simply ignores the secret-message data, but it can nevertheless be decoded at the other end, the team has found. 鈥淭he secret data is indistinguishable from silence-period traffic, so detection of SkypeHide is very difficult,鈥� says Mazurczyk. They found they could transmit secret text, audio or video during Skype calls at a rate of almost 1 kilobit per second alongside phone calls.
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The team aims to present SkypeHide at a steganography conference in Montpellier, France, in June. They have .
