Encryption is a very important way to secure data in storage and communication, and it is a process of encoding messages or information in such a manner that only authorised persons can access it. Different techniques are used to protect confidential image data against illicit access. In image encryption using chaotic systems, most authors use or design algorithms to generate the initial parameters’ values from the secret key. However, as the key size depends on the number of these parameters, the used algorithms show little sensitivity to small changes in the key. To enhance both security and sensitivity in the choice of the initial parameters, this work combines the use of the Grain-128a stream cipher algorithm with two-dimensional Zaslavsky chaotic map. Firstly, the Grain-128a algorithm is applied to generate the required parameters of Zaslavsky's chaotic map from a fixed length 256-bit secret key. Secondly, the sequences generated by the chaotic map are used to encrypt the image using a bit confusion and diffusion process. The simulation results on greyscale, colour, binary, indexed, and medical images together with the scores obtained in the evaluation of the algorithm show that the proposed method is very sure and effective in encrypting images of any size and any type.

中文翻译：

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结合使用Grain-128a算法和Zaslavsky混沌图进行图像加密

加密是保护数据在存储和通信中的一种非常重要的方式，它是对消息或信息进行编码的过程，只有授权人员才能访问它。使用不同的技术来保护机密图像数据免遭非法访问。在使用混沌系统的图像加密中，大多数作者使用或设计算法从秘密密钥生成初始参数的值。但是，由于密钥大小取决于这些参数的数量，因此所使用的算法对密钥的细微变化几乎不敏感。为了提高初始参数选择的安全性和敏感性，这项工作结合了使用Grain-128a流密码算法和二维Zaslavsky混沌图。首先，应用Grain-128a算法从固定长度的256位密钥生成Zaslavsky混沌图的所需参数。其次，混沌映射生成的序列用于通过位混淆和扩散过程对图像进行加密。在灰度，彩色，二进制，索引和医学图像上的仿真结果以及在算法评估中获得的分数表明，所提出的方法在加密任何大小和任何类型的图像方面都是非常可靠和有效的。