Abstract
Steganography based on bits-modification of speech frames is a kind of commonly used method, which targets at RTP payloads and offers covert communications over voice-over-IP (VoIP). However, direct modification on frames is often independent of the inherent speech features, which may lead to great degradation of speech quality. A novel frame-bitrate-change based steganography is proposed in this work, which discovers a novel covert channel for VoIP and introduces less distortion. This method exploits the feature of multi-rate speech codecs that the practical bitrate of speech frame is identified only by speech decoder at receiving end. Based on this characteristic, two steganography strategies called bitrate downgrading (BD) and bitrate switching (BS) are provided. The first strategy substitutes high bit-rate speech frames with lower ones to embed secret message, which introduces very low distortion in practice, and much less than other bits-modification based methods with the same embedding capacity. The second one encodes secret message bits into different types of speech frames, which is an alternative choice for supplement. The two strategies are implemented and tested on our covert communication system StegVoIP. The experiment results show that our proposed method is effective and fulfills the real-time requirement of VoIP communication.
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Foundation item: Project(2011CB302305) supported by National Basic Research Program (973 Program) of China; Projects(61232004, 61302094) supported by National Natural Science Foundation of China; Project(ZQN-PY115) supported by Promotion Program for Young and Middle-aged Teacher in Science and Technology Research of Huaqiao University, China; Project(JA13012) supported by Education Science Research Program for Young and Middle-aged Teacher of Fujian Province of China; Project(2014J01238) supported by Natural Science Foundation of Fujian Province of China
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Liu, J., Tian, H. & Zhou, K. Frame-bitrate-change based steganography for voice-over-IP. J. Cent. South Univ. 21, 4544–4552 (2014). https://doi.org/10.1007/s11771-014-2459-5
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DOI: https://doi.org/10.1007/s11771-014-2459-5