Covert VoIP Communication based on Audio Steganography

Abstract

Voice over Internet Protocol (VoIP) is a popular and important internet protocol for real-time voice calling. It is used in several software applications such as Skype, WhatsApp, and Google Talk. However, communications over the internet can easily be exposed to hacking and eavesdropping. In secret communication, a private channel with robust encryption can provide the required protection for the communications. But private channels have more constraints than the public channel, such as specific communication devices and specific regions to cover. On the other hand, public communications such as VoIP can be done from anywhere without extra costs. This paper proposes a real-time covert communication approach that generates a secret speech channel inside a public speech channel based on audio steganography. The process requires high embedding capacity in a real-time manner. Therefore, the proposed approach encodes the secret speech using Internet Low Bit Rate Codec (iLBC) that can be used as a VoIP source Codec to compress the secret input speech with auto-correction for speech quality degradation over a lossy channel. Also, the cover speech is compressed by G.711 encoder at synchronous time periods (for each 20 ms) with respect to the secret speech to meet the requirements of the VoIP. Subsequently, the secret data hides in compressed cover speech data in real-time. The embedding procedure employs the only high strength data to maintain the quality of the cover data after embedding at greater than 40 dB in terms of signal-to-noise ratio (S NR). The secret data is 100% retrieved without error in the case of a lossless channel. This approach can be used in secure communications such as military and government communications.