Encryption and decryption using a sandwich phase diffuser made by using two speckle patterns and placed in the Fourier plane: Simulation results

In the present paper, we describe the encryption and decryption of two-dimensional images. The encryption is done by employing a sandwich phase diffuser made by using two elongated speckle patterns, and placed in the Fourier plane of a double random phase encoding system. After encryption, the two constituent phase diffusers of such a sandwich diffuser are separated. During decryption, if the conjugate of either of the two elongated phase speckle patterns is used, the image cannot be retrieved. Correct decryption is also not possible if a sandwich diffuser with any of the phase speckle patterns is shifted in position with respect to the other. For decryption, the encrypted image is Fourier transformed and multiplied by the conjugate of the sandwich diffuser, and then the product is further Fourier transformed. It is possible to generate the image only if both the elongated phase speckle patterns are matched point-to-point and then the proper conjugate is made. The use of elongated speckle patterns in constituting a sandwich phase diffuser makes the system less complicated as compared to the use of a sandwich diffuser made with normal speckle patterns, enabling an easy alignment of the random phase diffuser at the time of rejoining the constituent diffusers for making the right key. The ease of alignment is due to the reduction of the requirement of 360° scanning at the time of rejoining these diffusers with little reduction in the security of the system. Simulation results are presented in support of the proposed idea. For optical implementation, the decrypted image may be obtained by generating a phase conjugate wave by the phase conjugation technique, and passing through the same sandwich phase diffuser. To evaluate the reliability of the technique, mean square error (MSE) between the decrypted and original image has been calculated.     

基于级联相位恢复算法的光学图像加密

在虚拟光学数据加密理论模型的基础上,提出了一种光学图像加密的可视化密码构造算法。该加密算法基于自由空间传播的光学系统,利用级联迭代角谱相位恢复算法把待加密图像分别编码到两块相位模板之中,从而实现图像的加密。该加密技术不但可通过同时调整两块相位模板的相位分布的搜索策略来扩大搜索空间,提高安全强度,而且扩大了系统密钥空间,使系统获得更高的安全性,且能通过简单的数值运算或光学实验装置得到质量非常高的解密图像,还从理论上分析了该算法的时间复杂度。计算机模拟结果表明,该加密算法的收敛速度快,能迅速找到非常好的近似解,解密图像质量高且系统安全性良好。     

双随机相位图像加密的实值编码研究

提出了一种基于双随机相位的图像实值编码方法,该方法可应用于光学图像加密.要编码的纯相位图像分别在空间域和频域加入随机相位掩膜,其中在频域将编码范围扩大4倍,经过光学系统的变换,将生成的图像取实部作为编码图像.实值编码的图像利用与编码过程类似的方法进行解码,可以准确地重建原图像.该编译码方法简单,编码图像是一个近似随机噪声的实值图像,便于数字图像的传输与输出.     

基于随机相位实值编码的光学图像加密

提出了一种用于图像加密的随机相位实值编码方法,待编码的纯相位图像与一个随机相位掩膜一起作傅里叶变换,取其实部作为编码图像.已编码的图像和随机相位掩膜的傅里叶变换相加作傅里叶反变换,反变换的光强可以准确地重建原图像.该编译码方法简单,编码图像是一个实值图像,便于计算机打印或显示输出.     

Establishing the broadcast efficiency of the Subset Difference Revocation Scheme

When an organisation chooses a system to make regular broadcasts to a changing user base, there is an inevitable trade off between the number of keys a user must store and the number of keys used in the broadcast. The Complete Subtree and Subset Difference Revocation Schemes were proposed as efficient solutions to this problem. However, all measurements of the broadcast size have been in terms of upper bounds on the worst-case. Also, the bound on the latter scheme is only relevant for small numbers of revoked users, despite the fact that both schemes allow any number of such users. Since the broadcast size can be critical for limited memory devices, we aid comparative analysis of these important techniques by establishing the worst-case broadcast size for both revocation schemes.      

A variant of Boneh-Franklin IBE with a tight reduction in the random oracle model

The first practical identity based encryption (IBE) scheme was published by Boneh and Franklin at Crypto 2001, based on the elliptic curve pairing. Since that time, many other IBE schemes have been published. In this paper, we describe a variant of Boneh-Franklin with a tight reduction in the random oracle model. Our new scheme is quite efficient compared to existing schemes; moreover, upgrading from Boneh-Franklin to our new scheme is straightforward.      

基于可编程器件的Rijndael加密算法优化实现

本文针对无线传感器网络传感器节点处理能力弱、携带能量低的特点,提出基于Rijndael算法优化的数据加密技术.通过对Rijndael加密算法的数据存储、列混合以及轮变换等特点的分析,提出对于加密算法的优化建议,采用可编程逻辑器件对优化后的加密算法进行设计和实现,并进行加密验证,同时对优化后加密算法的数据处理速率、算法功耗、逻辑资源占用情况进行评估.由实验结果可知,优化后的Rijndael加密算法相比优化之前有很大的突破,能够适用于无线传感器网络的数据加密.     

基于干涉原理的双图像加密系统

提出一种新的虚拟光学加密方法,该方法分3个步骤将两幅图像隐藏于3个随机相位板中。将两幅图像分别作为相位和幅度信息隐藏于一个复数场中,利用随机相位板作为参考光,并采用数字全息术将该复数场转换成平稳随机白噪声,利用干涉加密原理进一步将此白噪声储存于2个随机相位板中,从而将两幅图像信息隐藏于3个纯随机相位板中。该方法原理简单,无需进行迭代操作。计算机模拟结果显示:任何一个密钥错误,均无法得到原始图像的任何信息。同时,解密过程对系统中距离及波长等参数非常敏感,较大地提升了系统的安全性。     

Cryptanalysis on an image block encryption algorithm based on spatiotemporal chaos

An image block encryption scheme based on spatiotemporal chaos has been proposed recently.In this paper,we analyse the security weakness of the proposal.The main problem of the original scheme is that the generated keystream remains unchanged for encrypting every image.Based on the flaws,we demonstrate a chosen plaintext attack for revealing the equivalent keys with only 6 pairs of plaintext/ciphertext used.Finally,experimental results show the validity of our attack.     

一种无密钥托管的移动IPv6网络匿名密钥分发协议

针对基于身份的密码体制IBE中固有的密钥托管问题,本文提出了一个移动IPv6网络环境中的无密钥托管匿名密钥生成机制与分发协议.该机制将节点身份认证和密钥生成与分发这两个过程分离,利用不可区分性匿名密文安全性在PKG不知道节点地址的情况下分发私钥给经过身份认证的节点,使得私钥生成中心或认证中心即使被单独攻破,攻击者也无法实现身份碰撞.可将身份认证中心部署于家乡服务器,而将PKG离线部署.经安全性分析,协议有效解决了移动IPv6网络中基于身份密码体制的密钥托管问题.