Polish researchers have developed a range of steganographic techniques which would enable a hacker to hide information in VoIP traffic.
Steganography has been in existence for a considerable time, but it has been mainly used to hide information in standard data traffic.
The researchers, Wojciech Mazurczyk and Krzysztof Szczypiorski, have proposed three techniques for hiding information in voice traffic. Like traditional steganography, their techniques can be dangerous to organisations because of the risk of leakage of confidential information.
Mazurczyk and Szczypiorski, both network security researchers at the Warsaw University of Technology, revealed their findings in an article written exclusively for SC Magazine (see related articles). They are dubbing their techniques "steganophony": the combination of steganography and telephony.
Their techniques are called LACK, HICCUPS and security mechanism steganography.
LACK conveys the hidden information in intentionally delayed voice packets. Because VoIP receivers discard delayed packets, the hidden information should get through undetected.
HICCUPS can be used in voice over wireless LAN deployments and uses corrupted frames with bad checksums to avoid detection.
Security mechanism steganography alters security data, such as authentication tags, in each RTP packet in order to facilitate hidden information. The researchers argue that this technique will evade active wardens, which are systems or processes trying to detect hidden packets.
"Because the number of steganographic methods is high, and there is no single method to detect them, we should consider steganography in VoIP as a threat to organisations' security," the researchers wrote.
Up to 1.3Mbps of information can be hidden in VoIP traffic in each direction, they found.