Steganography in vector quantization process of linear predictive coding for low-bit-rate speech codec

In this paper, we focus on quantization-index-modulation (QIM) steganography in low-bit-rate speech codec and contribute to improve its steganalysis resistance. A novel QIM steganography is proposed based on the replacement of quantization index set in linear predictive coding (LPC). In this method, each quantization index set is seen as a point in quantization index space. Steganography is conducted in such space. Comparing with other methods, our algorithm significantly improves the embedding efficiency. One quantization index needs to be changed at most when three binary bits are hidden. The number of alterations introduced by the proposed approach is much lower than that of the current methods with the same embedding rate. Due to the fewer cover changes, the proposed steganography is less detectable. Moreover, a division strategy based on the genetic algorithm is proposed to reduce the additional distortion introduced by replacements. In our experiment, ITU-T G.723.1 is selected as the codec, and the experimental results show that the proposed approach outperforms the state-of-the-art LPC-based approach in low-bit-rate speech codec with respect to both steganographic capacity and steganalysis resistance.