在虚拟光学数据加密理论的基础上,基于光学4f系统及迭代傅里叶变换算法(IFTA),提出利用多个相位板进行分级图像加密的方法,将不同密级的图像分别加密到不同的相位板中,给出其理论原理和实现方法,并通过计算机模拟验证了该方法的有效性。在解密过程中,利用不同数目的相位板可以得到不同图像,相位板越多,得到的图像也就越多。随着相位板数目的增加,要想得到正确的解密图像,相位板放置的次序也有严格要求,系统的安全性也因此大大提高。此方法可将信息进行分级加密,用于对不同权限级别的用户开放,也可用于安全认证和准入检查系统。

A novel approach - multiple phase encoding for hierarchical security by use of a 4f optical system and iterative Fourier transform algorithm (IFTA) is presented, which is based on the methodology of virtual optics. Two or more phase masks produced by multiple IFTA are used in this hierarchical security system, in which different target images can be retrieved by use of different numbers of phase masks. The more numbers of phase masks the user has, the more images he can get. In addition to numbers of the phase masks, the sequential order of the phase masks is introduced to increase the system security. Simulation results are demonstrated to verify the proposed method.