Securing digital voice communication using non-autonomous modulated chaotic signal

In this paper, we present an encryption approach for voice communication systems based on direct chaotic modulation (non-autonomous modulation), in which voice is injected into one variable of the master system (using either Lorenz chaotic flow or Qi hyperchaotic flow) without changing the value of any control parameter. This approach is based on the change of chaotic signal by injecting voice samples into one variable in chaotic system and hence generating a new chaotic signal. The voice signal is then extracted from the chaotic signal in the receiver side. Furthermore, we use a high dimension chaotic flow which increases the security of the encrypted signal. Non-autonomous modulation technique is suitable for secure real-time applications. We also presented a comparative study between the two approaches with their conventional chaotic masking counterparts. Experimental results show that non-autonomous methods give better performance than their chaotic masking counterparts when they are analyzed against Signal-to-Noise-Ratio (−38.55 dB vs. 38.51 dB and 59.22 dB vs. 58.11 dB), Segmental signal-to-Noise-Ratio (38.91 dB vs. 38.84 dB and 54.20 dB vs. 53.16 dB), Log-Likelihood Ratio (0.88 vs. 0.80 and 1.59 vs. 1.50), and Correlation Coefficient Analysis (0.0345 vs. 0.021 and 0.0002 vs. 0.01012). Statistical analyses show that the second proposed approach has the best results for the encrypted signal. Modifying conventional chaotic approaches increases the security of the encryption system.