By JR Raphael
Contributing Writer, [GAS]

A couple of Polish scientists have come up with a way to encode secret messages within the data of internet-based VoIP calls.

The men, from the Institute of Telecommunications in Warsaw, designed a steganographic system — a special kind of code that allows content to be encrypted inside of other content, unbeknownst to anyone else. The idea has been used before to encode information within an image that can then be detected using specialized software, but the scientists say their work would be the first time encryption has been used in an audio-based phone call.

One of the researchers explained the process to New Scientist Magazine (subscription required):

“You replace some of the voice data packets that you are sending with the hidden message. This is possible because VoIP uses a data transmission routine called the User Datagram Protocol (UDP). Unlike the more familiar TCP, which delivers web pages and emails, UDP does not guarantee that packets will arrive in the same order they were sent. They may arrive out of order, be duplicated, or simply go missing. The fact that the voice message can survive when VoIP packets are lost means that some of them can be used for another message: the hidden one.”

The pair is now working to further control the effect the hidden messages have on the call’s audio quality to make sure the process stays undetected. So how would this technology be used? The scientists say it’s open to interpretation.

“Whether we treat VoIP covert channels as a potential threat to network security or as a mean to improve VoIP functionality, we must accept the fact that the number of information that we can covertly transfer is significant,” the researchers concluded.