A New Data-Hiding Approach for IP Telephony Applications with Silence Suppression

Even if information hiding can be used for licit purposes, it is increasingly exploited by malware to exfiltrate data or to coordinate attacks in a stealthy manner. Therefore, investigating new methods for creating covert channels is fundamental to completely assess the security of the Internet. Since the popularity of the carrier plays a major role, this paper proposes to hide data within VoIP traffic. Specifically, we exploit Voice Activity Detection (VAD), which suspends the transmission during speech pauses to reduce bandwidth requirements. To create the covert channel, our method transforms a VAD-activated VoIP stream into a non-VAD one. Then, hidden information is injected into fake RTP packets generated during silence intervals. Results indicate that steganographically modified VAD-activated VoIP streams offer a good trade-off between stealthiness and steganographic bandwidth.