In the 5th Century BCE, the Greek tyrant Histiaeus devised a clever new way to send hidden messages. He shaved the head of one of his servants, tattooed the missive on his head, and waited for his hair to grow back before sending the messenger out. When the courier arrive, his head was shaved and the message was read, giving information about upcoming Persian attacks.
Though Histiaeus may not have known as much, he was one of the early practitioners of steganography, the practice of hiding one message inside another, innocent-looking message. Later on, secret inks were used, and Morse code messages were woven into a sweater was worn by a courier. Now, thanks to VoIP and applications like Skype, steganography is undergoing another revolution,* IEEE Spectrum *reports.
As communication turned to bits and bytes rather than paper and ink, steganography followed suit. Binary codes could be hidden in an image file, or an mp3 audio file, and then decoded using simple software. But this practice had limits: the file’s size would grow with the messages embedded, and long messages would make files so large they’d raise a red flag.
Internet Protocol, commonly known as IP, governs the way information is sent around the Web. IP breaks the information into tiny parts, known as packets, and then routes them all to the desired destination. When the packets arrive with the receiver, they’re out of order—IP puts the information back together, and delivers it the final step. A few standards were changed, and Voice Over Internet Protocol, VoIP, became the de facto way of facilitating voice and video.
VoIP uses a series of protocols to essentially create an open, unmediated link between two computers. VOIP applications also provide a way to make sure the packets are ordered quickly and correctly -- and deal with latencies in the network. Information flows more quickly and fluidly. And that's a goldmine for anyone trying to send hidden messages.
There’s only the smallest possible time for interception to happen since all data is stored locally rather than redirected through a central server. Plus, since so much data is being sent back and forth, large messages can be sent without causing any alarm. Unlike an image or video, which can be downloaded and analyzed at anytime, there’s no way to get at and store files sent with VoIP.
IEEE Spectrum found three different ways that messages could be encrypted and sent via VoIP, with little or no possibility for detection or interception. By delaying specific packets, corrupting packets, or changing the identification information of packets, users can sort out their message, which is then easily decoded by freely available software. In the course of a Skype call that only lasts a few minutes, massive amounts of data can be sent—without any detection or permanent record.
Steganography has positive implications – concealing sources for journalists, talking without government censorship – but it’s also a potential hiding point for terrorists. A 2001 USA Today* *article described fake eBay listings in which routinely altered pictures of a sewing machine contained malevolent cargo.“ Which side VoIP helps more, remains to be seen.
[Photo: via Southern Polytechnic]
