A Steganographic Method Based on High Bit Rates Speech Codec of G.723.1

摘要

With compressed speech codecs having been widely used as the key technology for VoIP and mobile communications, steganography based on compressed speech streams has been flourishing in recent years. In this paper, based on the codec's characteristic features, we present a steganographic method using the excitation pulse positions of the high bit rate speech codec of ITU-T G.723.1. In the proposed method, the codes of excitation pulse-positions in the speech codec (i.e., codebook positions) are finely modulated according to the secret information that is being hidden. Sensitive data may thus be transmitted in secret without affecting the transmission quality of the normal speech data. Using the algorithm developed in this work and with the all-odd/even characteristics of pulse code positions being utilized, steganography experiments at high bit rates (6.3 Kbit/s) ware conducted on four kinds of voices: male or female voices speaking Mandarin or English. By using the proposed approach, an embedding rate of 2.6% and secret information transfer rate of 166 bits/s resulted in <5.0% degradations of the Perceptual Evaluation of Speech Quality (PESQ) score. And when the data hiding capacity reached 8.8% and the rate of secret information transfer came to 566 bits/s, the PESQ score was still reduced by <12.1%. The experiments show that our algorithm performs a higher degree of secrecy and steganographic efficacy compared with existing similar algorithms.