In this paper, an asymmetric cryptosystem with unequal modulus decomposition in the Fourier domain is presented. The input-colour image is decomposed into its red, green, and blue components. Each component is bounded with random phase mask and undergoes Fourier Transform followed by unequal modulus decomposition. One of resulting masks acts as first private key and other one is again Fourier Transformed and undergoes unequal modulus decomposition. Further two masks are obtained, where one acts as second private key and other is phase truncated to obtain encrypted image. Encrypted image is attenuated by a factor and appended with host image to obtain watermarked image. Numerical simulations on MATLAB are performed for authenticating and validating proposed scheme. Statistical, correlation distribution, information entropy and histogram analyses are performed to demonstrate scheme efficacy. The results illustrate that the scheme resists classical cryptographic, special and occlusion attacks. The proposed scheme is also highly sensitive to its private keys and attenuation factor.

在本文中，提出了一种在傅里叶域中具有不等模分解的非对称密码系统。输入彩色图像被分解为红色、绿色和蓝色分量。每个分量都以随机相位掩模为界，并经过傅立叶变换，然后进行不等模分解。生成的掩码之一充当第一私钥，另一个掩码再次进行傅立叶变换并进行不等模分解。获得另外两个掩码，其中一个充当第二私钥，另一个被相位截断以获得加密图像。加密后的图像经过一个因子衰减后附加宿主图像，得到带水印的图像。在 MATLAB 上进行数值模拟以验证和验证所提出的方案。统计，相关分布，执行信息熵和直方图分析以证明方案的有效性。结果表明，该方案能够抵抗经典密码、特殊和遮挡攻击。所提出的方案也对其私钥和衰减因子高度敏感。