The security, efficiency, and storage of image data are global issues while transmitting images over the Internet. In this paper, we have fabricated a novel approach for security of multiple-color images utilizing asymmetric RSA cryptosystem, reality preserving fractional discrete cosine transform and Arnold transform. In our approach, three indexed images are obtained from three $\mathsf{RGB}$ color images by extracting their color maps. These three indexed images are taken as red, green and blue components of an $\mathsf{RGB}$ color image. Each element of an $\mathsf{RGB}$ image is first encrypted using RSA cryptosystem. The fractional discrete cosine transform is applied on the partially encrypted image which transforms the image data from the time domain to the frequency domain. Finally, Arnold transform dislocates the processed image. The security of the similar encryption schemes available in literature depends upon the secret keys only. If the secret keys are leaked, the encryption scheme is no more secure. Also, these schemes are secure either in the time domain or in the frequency domain. However, the security of our approach depends upon secret keys and their proper arrangements. The proposed method is secure in the time domain as well as in the frequency domain. Due to a single encrypted image, it is easy for storage and transmission over the Internet. Simulation analysis is done with standard examples to conclude that the proposed approach is robust.

在通过Internet传输图像时，图像数据的安全性，效率和存储是全球性的问题。在本文中，我们利用非对称RSA密码系统，保真度分数离散余弦变换和Arnold变换，构造了一种用于保护多色图像的新颖方法。在我们的方法中，从三个位置获得三个索引图像$\mathsf{RGB}$通过提取颜色图来对它们进行彩色处理。这三个索引图像分别作为红色，绿色和蓝色分量的$\mathsf{RGB}$彩色图像。每个元素$\mathsf{RGB}$首先使用RSA密码系统对图像进行加密。分数离散余弦变换应用于部分加密的图像，该图像将图像数据从时域转换到频域。最后，Arnold变换使处理后的图像移位。文献中可用的类似加密方案的安全性仅取决于秘密密钥。如果密钥泄露，则加密方案将不再安全。而且，这些方案在时域或频域中都是安全的。但是，我们方法的安全性取决于秘密密钥及其适当的安排。所提出的方法在时域和频域中都是安全的。由于具有单个加密图像，因此很容易在Internet上进行存储和传输。