Speech encryption algorithm using FFT and 3D-Lorenz–logistic chaotic map

In this paper a new speech encryption method using Fast Fourier Transform (FFT) and multiple chaotic maps has been developed for secured speech communication. In order to improve the drawbacks namely residual intelligibility in encrypted signal, poor quality in decrypted signal, low key space and high computational complexity that prevail in the exist speech encryption methods, a novel speech encryption algorithm based on a three dimension (3D) Lorenz-Logistic map has been developed. A new 3D Lorenz-Logistic map has been introduced by feeding Logistic map in 3D Lorenz map to obtain three different random number sequences. Totally eight initial and controlling parameters of 3D Lorenz-Logistic map are used as key values. The behavior of chaotic map is totally changed by changing the key values which generates highly randomized number sequence. Permutation and substitution plays vital role in this method. The input speech is applied to FFT to obtain real as well as imaginary values. Two random number sequences of the 3D Lorenz-Logistic map are used to permute the real and imaginary values of input speech signal. Remaining one random number sequence is used to permute a reference speech sample which is used for substitution of permuted real values of speech signal. The reverse process of permutation and substitution is used for recovering the desired signal. The Inverse Fast Fourier Transform (IFFT) is applied to reconstruct the original signal. The performance of the proposed method is verified using histogram analysis, spectrogram analysis, correlation analysis, signal to noise ratio analysis, NSCR (Number of Samples Changing Rate) and UACI (Unified Averaged Changed Intensity) analysis, key space and key sensitivity analysis, computational complexity measure, Perceptual Evaluation of Speech Quality (PESQ) analysis and subjective evaluation of speech quality. The results evidence that the proposed speech encryption method provides better security system with robust decryption quality.