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In this paper, we present a very simple and efficient hybrid encryption algorithm based on block and stream ciphers using chaotic systems. Due to the specific characteristics of chaotic systems which are described by a set of nonlinear deterministic dynamic equations, chaos-based encryption achieves a very high level of security. The chaotic system used in this algorithm is Chirikov Standard Map, which is chosen in order to further minimize the encryption time. The proposed scheme adopts two main operations one to generate pseudorandom data block that will be used for stream cipher, and the second to create substitution and permutation tables in initial step and perform rounds for confusion and diffusion processes in block cipher. Some cryptographic tests and metrics are applied to measure the degree of security and analyze the performance of the encryption scheme. The evaluation and simulation analysis indicate that our proposal possesses excellent cryptographic properties; it is extremely sensitive to the small change in secret key, resists against common cryptanalytic attacks, has a high speed and easy to implement.

This paper presents a very simple and efficient encryption scheme based on controlled chaotic maps and ADPCM (Adaptive Differential Pulse Code Modulation) coding, in order to secure the real-time voice communication for operating at 16, 24, 32 or 40 kbps. This encryption algorithm adopts three main operations one to generate chaotic values using two chaotic logistic maps starting from independent initial conditions, the second to transform them into binary words using random encoding tables and the third to execute some basic operations and substitutions. It has important properties of randomness that can pass NIST batteries of tests. The evaluation and simulation analysis indicate that our proposal possesses an excellent statistical and cryptographic properties; it provides low correlation between adjacent samples in encryption speech, extremely sensitive encryption keys and has a large key space which is sufficient to protect against brute-force attack. As an illustrative example, an application on a commonly-encoder type used in communications, standard ITU-T G.726, is presented.

We propose to incorporate encryption procedure into the lossy compression of voice data PCM(Pulse Code Modulation) based on the A-law approximation quantization. The proposed codec CPCM (Chaotic Pulse Code Modulaion) will join the encryption to the compression of the voice data. This scheme provides the same compression ratio given by the PCM codec, but with an unintelligible content. Comparisons with many used schemes have been made to highlight the proposed method in terms of security and rapidity. CPCM codec can be a better alternative to Compress-then-encrypt classical methods which is a time and resource consuming and non suitable for real-time multimedia secure transmission.

This paper presents a new secure variant of ADPCM encoders that are adopted by the CCITT as Adaptive Differential Pulse Code Modulation. This version provides encryption and decryption of voice simultaneously with operations ADPCM encoding and decoding. The evaluation of the scheme showed better performance in terms of speed and security.