Hiding Secret Messages In Skype Silences 79
Orome1 writes "A group of researchers from the Institute of Telecommunications of the Warsaw University of Technology have devised a way to send and receive messages hidden in the data packets used to represent silences during a Skype call. After learning that Skype transmits voice data in 130-byte packets and the silences in 70-byte packets, the researchers came upon the idea of using the latter to conceal the sending and receiving of additional messages."
Re:Eloquent silence (Score:4, Interesting)
Exactly what I was thinking.
You would think that a packet specifying X seconds of simulated silence could be packed into a few bits, so maybe two bytes should suffice.
Clearly there is something else going on, or they would not have designed such a large packet to "represent silence".
That one can distinguish the silence packets from the voice packets doesn't speak too well of the encryption that Skype has always claimed they use.
If the Skype client didn't send packets during 'silence', then the client on the receiving end of an extended silent session wouldn't know whether there was silence on the other end or a network problem. That's why the client keeps sending packets even during "silence" rather than just timing silent sections then sending out a packet at the end of the silence saying "It was silent for the past 10 seconds, so that's why you didn't receive any data from me".
Re:Eloquent silence (Score:2, Interesting)
My guess is they even added in the 38 byte ethernet overhead. Yielding 66 bytes. Add 4 bytes for the codec and its fairly reasonable.
Of course they probably didn't use the 8021q ethernet overhead which is 42 bytes, or they wouldn't have any payload at all! (I suppose its possible... an empty payload is intuitively about as "silent" as you can get)