Silence Turned Into Secret Skype Messages


A team of encryption specialists has figured out a way to communicate with each other using silence. No, it’s not a Cold War era spy trick, but it’s still very tricky. Welcome to SkypeHide.

The group that created the technique for SkypeHide was led by Wojciech Mazurczyk, an assistant professor of computer networks and switching at the Warsaw University of Technology. Mazurczyk and his colleagues specialize in network steganography. Spy nerds know that’s the science of hiding information and messages within computer networks.

SkypeHide works using something called “packet hijacking.” Mazurczyk, along with Maciej Karaś and Krzysztof Szczypiorski, found that whenever we use Skype, the program keeps sending 70-bit data packets during the silences that occur within a conversation. So the computer scientists put their own secret messages into those data packets, according to Nancy Owano at

Mazurczyk told Owano, “The secret data is indistinguishable from silence-period traffic, so detection of SkypeHide is very difficult.” This opens up the potential to transmit secret text, audio files and even video during a red herring conversation that’s happening. At best, the speed for transmitting these secret messages was 1 kilobit per second, which isn’t superfast but could be fast enough to communicate something important.

Spy techniques can backfire, though. What if this technique gets into the wrong hands? Hopefully that long pause between birthday greetings doesn’t end up being an ideal time for terrorists to touch base. If secret messages are discovered and have a criminal connection, a law enforcement entity could compel Skype to share messages stored temporarily on its server.

Skype does tells its users to be careful. As much as the site tries to protect users, the site can’t guarantee their safeguards “will prevent every unauthorized attempt to access, use or disclose personal information.”

More answers may be forthcoming later this summer, when the Warsaw University of Technology group plans to present SkypeHide at the ACM Workshop on Information Hiding and Multimedia Security in Montpellier, France. In the meantime, if you want to send some secret spy messages, there’s always the classics: a red flag in the flowerpot or the chalk mark on the mailbox.

Photo Credit: Hotblack

Invalid Email