The images transmission become more and more widely used in everyday life and even have been known to be vulnerable to interception and unauthorized access. The security of their transmission became necessary. In this paper an improved version of the Achterbahn-128 for image encryption and decryption have been proposed. The proposed design is based on seventeen binary primitive nonlinear feedback shift registers (NLFSRs) whose polynomials are primitive and a nonlinear Boolean function. The outputs of seventeen registers are combined by the nonlinear Boolean function to produce keysteam sequence. The proposed scheme is compared to a Achterbahn-128. The results of several experimental, statistical analysis and sensitivity analysis show that the proposed image encryption scheme is better than Achterbahn-128 and provides an efficient and secure way for image encryption and transmission.

The aim of this contribution is to enhance the security of encrypted image and decrease the execution time. The proposed cryptosystem based on the keystream generator (KSG) inspired from achterbahn-128 characterized by some good properties used for generating the key. The scan pattern is utilized for the mapping of the image encryption. After the generation of the keystream, the image is encrypted vertically using the scan pattern partition, and then the encrypted image is permuted and rescanned horizontally. Several tests are done using MATLAB software in order to prove performances of the system, including the statistical tests, the sensitivity analysis, and the security analysis. The proposed technique is simple to implement and has high encryption rate.

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