Silent Skype calls can hide secret messages
Silent Skype calls can hide secret messages
Mazurczyk and his colleagues Maciej Kara? and Krzysztof 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.
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. "The secret data is indistinguishable from silence-period traffic, so detection of SkypeHide is very difficult," 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.
The team aims to present SkypeHide at a steganography conference in Montpellier, France, in June.