This paper introduces a speech encryption approach, which is based on permutation of speech segments using chaotic Baker map and substitution using masks in both time and transform domains. Two parameters are extracted from the main key used in the generation of mask. Either the Discrete Cosine Transform (DCT) or the Discrete Sine Transform (DST) can be used in the proposed cryptosystem to remove the residual intelligibility resulting from permutation and masking in time domain. Substitution with Masks is used in this cryptosystem to fill the silent periods within speech conversation and destroy format and pitch information. Permutation with chaotic Baker map is used in to maximize the benefits of the permutation process in encryption by using large-size blocks to allow more audio segments to be permutated. The proposed cryptosystem has a low complexity, small delay, and high degree of security. Simulation results prove that the proposed cryptosystem is robust to the presence of noise.

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This paper introduces a new speech cryptosystem, which is based on permutation and masking of speech segments using multiple secret keys in both time and transform domains. The main key is generated, randomly, using a Pseudo Noise (PN) sequence generator, and two other keys are generated from the main key to be used in the subsequent rounds of encryption. Either the Discrete Cosine Transform (DCT) or the Discrete Sine Transform (DST) can be used in the proposed cryptosystem to remove the residual intelligibility resulting from permutation and masking in the time domain. In the proposed cryptosystem, the permutation process is performed with circular shifts calculated from the key bits. The utilized mask is also generated from the secret key by circular shifts. The proposed cryptosystem has a low complexity, small delay, and high degree of security. Simulation results prove that the proposed cryptosystem is robust to the presence of noise.

This paper presents an analog speech cryptosystem based on permutation and substitution of speech segments. Permutations processes and substitutions masks are variables which changed with changing the secret key. The main target of proposed system is to get non standard processes to decrease the complexity and diffusion of the system without affecting its security and depend on different security aspects like hidden block size and algorithm. We present a security analysis for the proposed cryptosystem against the brute-force and the statistical attacks from a strict cryptographic viewpoint. Experimental results verify and prove that the proposed speech cryptosystem is highly secure from the cryptographic viewpoint. It is shown that the permutations and substitutions induced by the new algorithm behave as typical random processes and can't be predicted without the knowledge of the secret key. The results prove that this proposed cryptosystem has a very powerful diffusion mechanism to its secret key and increases robust to noise.