A Cryptic Encoding Method for G.729 Using Variation in Bit‐reversal Sensitivity

We propose a method of keeping conversations secret using the differences in the amount of degradation (bit-reversal sensitivity) in decoded speech when reversing the bits in the ITU-T standard 8-kbit/s sound encoding method G.729. In communications using the Internet or other open networks, there is a risk of eavesdropping by third parties, so the content of communications should be hidden using appropriate methods. In this paper we analyze the bit-reversal sensitivity in G.729 and propose an efficient method for creating secrecy based on these results. In the proposed method, the decoded speech is greatly distorted and secrecy is achieved by converting and operating on only 10 of 80 bits in the G.729 synthesis filter and excitation source. Using objective values we evaluated the efficiency of each operation and using subjective evaluations we confirmed that our method is good at maintaining secrecy. (C) 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(2): 63-71, 2007;