一种基于排列的(2,n)可视门限方案

像素扩展度和对比度是视觉加密方案中两个重要的指标，同时使二者达到最优在理论上是非常困难的。运用排列的方法设计出一种(2，n)方案，从理论上证明了其存在性，并给出了该方案的构造方法。软件仿真结果表明，该方案能够折衷考虑二者之间的矛盾，在像素扩展度较小的情况下，使对比度接近最优。     

基于恒权码的(2,n)视觉密码方案

通过研究恒权码与(2,n)视觉密码方案的关系,利用steiner系统构造恒权码,提出了基于恒权码的(2,n)视觉密码方案,在证明其存在性的同时,给出了该方案的构造方法。与现有方案相比,能较好地折衷像素扩展度和相对差。实验结果表明,该方案在保证相对差接近极大值的前提下,大大降低了像素扩展度。     

一种可防止欺骗的可视密码分享方案

Naor和Sham提出的可视密码方案(VCS)是一种将秘密黑白图像加密到不同分享中的秘密分享方案,并且无须计算即可进行解密但是如果在解密过程中欺骗者提供了伪造的分享,秘密图像的解密将失败.该文给出了一利新的构造方法,可找出解密过程中的欺骗者.     

具有可信仲裁者的可视密码分享方案

介绍了(k ,n)门限可视密码分享方案((k ,n)-VCS),在此基础上以实际应用为背景,提出了具有可信仲裁者的可视密码分享方案((k ,n)-TAVCS)。通过密钥的控制,任意至少k幅的图像必须经过可信仲裁者的认可才可恢复出秘密图像,保留了(k ,n)-VCS的优点,在确保安全性的同时满足实际应用的需要。对该方案进行了分析,给出了仿真实验的结果。     

基于半色调技术的(2,2)可视密码方案

为解决传统可视密码像素膨胀及分存图像无意义等问题,提出一个基于半色调技术的（2,2）可视密码方案。方案中密图为黑白反色图像,利用半色调技术将一幅灰度图像处理后的半色调图像作为掩盖图像一,然后对其进行反色运算得到掩盖图像二,根据密图修改掩盖图像生成分存图像,叠加分存图像恢复密图。该方案符合可视密码解密简单的特性且分存图像有意义、没有引入任何像素膨胀。     

可变可视密码

传统的可视密码在加密时会产生像素扩张,结果使分存图像比秘密图像大许多倍,尤其是应用在灰度和彩色图像上,其扩张的倍数更是惊人.传统的可视密码都是单点加密,本文在Hou的m点加密的基础上,提出任意点加密可视密码,即在加密的时候可以对任意个点进行加密,我们称之为可变可视密码.操作的时候,对秘密图像的r个点同时进行加密,当r=m时,该加密就是像素不扩展可视密码;当r>m时,该加密得到的就是分存图像缩小的可视密码(r的增大会降低解密图像的对比度);当r相似文献   

彩色图像的可视分存方案

利用矩阵并的思想给出了一般存取结构下分存图有意义的可视分存方案（称作扩展可视分存方案）,得到像素膨胀值,并且构造了一般存取结构的彩色图像扩展可视分存方案,得到彩色（k,n）扩展方案的最优像素膨胀.     

Visual secret sharing for multiple secrets

Conventional visual secret sharing schemes are designed for a single secret image so it is inefficient to generate numerous share images for multiple secret images simultaneously. Therefore, a novel visual secret sharing scheme for multiple secret images is proposed in this paper. In the proposed encryption process, a stacking relationship graph of secret pixels and share blocks is generated to indicate the encryption functions, and a set of visual patterns is defined to produce two share images according to this graph. Based on the stacking properties of these patterns, the secret images can be obtained from the two share images at aliquot stacking angles. The proposed scheme makes the number of secret images not restricted and further extends it to be general. As a result, the proposed scheme enhances visual secret sharing schemes’ ability for multiple secrets.     

一种基于秘密分享的高质量(k,n)可视加密算法

(k,n)可视加密算法是一种重要的信息隐藏算法。应用Shamir秘密分享的概念,将一幅二进制秘密图像隐藏在n幅分享图像中,通过在分享过程中增加随机性控制,保证生成的分享图像是接近噪声图像的无意义图像。从n幅无意义分享图像中,任意选取k幅分享图像,使用拉格朗日插值可提取秘密图像。该算法应用Shamir秘密分享来实现(k,n)可视加密,不需要码书,不会造成无限制的像素扩展。实验结果显示,该算法能实现(k,n)可视加密,提取秘密图像的提取正确率能保证100%。     

具有伪装图案的操作式多秘密视觉密码

将环形共享份划分为伪装区域和秘密区域,结合(2,2)单秘密视觉密码方案的基础矩阵,设计了一种具有伪装图案的操作式多秘密视觉密码方案.该方案不仅能够分享任意数量的秘密图像,而且改善了同类方案的像素扩展度和相对差,更重要的是共享份呈现出有意义的伪装图案,从而降低了攻击者对共享份的威胁.     

Visual multiple secret sharing based upon turning and flipping

The secret sharing schemes in conventional visual cryptography are capable of sharing one secret image into a set of random transparencies (called shares) in the form of rectangles, which reveal the secret image to the human visual system when they are superimposed. Recently, visual secret sharing schemes involving multiple secrets have attracted much attention. By adopting rotations on one of the two encoded circle shares, more than two secrets could be shared. Yet, the encoding and decoding processes of circle shares need more sophisticated mechanisms than those of rectangular or square ones. In this paper, we explore the possibilities of visual multiple secret sharing using simply two rectangular or square shares. Specifically, we define some operations onto a transparency based upon turning over or flipping around. Then we propose visual cryptographic schemes that are able to encode two or four secrets into two rectangular shares and up to eight secrets into two square shares such that the secrets cannot be obtained from any single share, whereas they are revealed by stacking the two shares under various combinations of turning or flipping operations. The proposed schemes, which solidly elaborate the relationship between the encoded shares and the shared secrets, broaden the research scope and enrich the flexibility and applicability of visual cryptography or image encryption theoretically and practically.     

基于三维立体分享图像的（2, 2）视觉密码方案

传统（2, 2）视觉密码方案由于其共享图像为毫无意义的二值图像而易引起攻击者的怀疑。为此,提出了一种基于三维立体分享图像的（2, 2）视觉密码方案。该方案将分享图像伪装成有意义的三维立体图,由此可较好地避免恶意攻击。而当两幅分享图像进行叠加等处理,人类视觉系统就能直接辨认出秘密信息。与其它图像加密方法的性能对比与定量评估说明：本方案在较好隐藏秘密信息的同时,具有相对较快的运算速度。正是由于该方案秘密恢复的简单性和有效性,因此具有广泛的应用前景。     

具有理想对比度的一般存取结构可视密码方案

本文提出了一种基于取反运算可获得理想对比度的可视密码方案,适用于一般存取结构可以实现秘密图像无失真地恢复,并且没有像素扩展。该方案应用了简单的布尔运算实现了传统可视密码方案中单纯的叠加运算无法实现的功能。     

A Study on Information Reservation for Visual Secret Sharing Method with Reversible Style

This paper discussed three conventional visual secret sharing methods with reversible property systematically and proposed a brand new information-reserved, non-expansion and reversible style visual secret sharing method. In all these approaches, fake contour effect has been tested and discussed, while on the other hand, an interleave approach has also been adopted. The proposed method could overcome such problems as information leak and slight fake contour effect that might occur while using the conventional visual secret sharing scheme in reversible style. Furthermore, the new method could enable the size of secret images to be equal to that of transparencies.     

Visual secret sharing by random grids revisited

Recently, the visual secret sharing (VSS) technique by random grids (RG), proposed by Kafri and Keren in 1987, has drawn attention in academia again to remove the abovementioned drawbacks. However, Kafri and Keren's scheme is a 2-out-of-2 VSS scheme but neither n-out-of-n nor 2-out-of-. In this paper, novel n-out-of-n (Method 1) and 2-out-of-n (Method 2) secret image sharing schemes based on RG are proposed to encrypt the secret into n cipher-grids without pixel expansion and additional codebook required. In the decryption phase, while participants superimpose all (Method 1) or at least two (Method 2) cipher-grids without any extra computation, the secret is recognizable by the human visual system. To our best knowledge, this paper is the first attempt in the literature to develop new RG-based VSS schemes by means of extending the basic 2-out-of-2 scheme to the n-out-of-n as well as 2-out-of-n ones. To demonstrate the correctness of the proposed schemes, the formal analysis is given while the experimental results show the proposed schemes do work well.     

具有优化对照度的灰度图像的可视分存方案

在可视分存方案（VCS）中,其解密过程通过人的视觉系统完成。对照度是VCS中重要的研究主题。现有复制设备提供了反色复制的基本功能,黑白图像的全黑反色方案（PBVCS）通过叠加一定数目的分存图像可以精确重构密图,从而为解决VCS重构图像质量问题提供了一种新的途径。给出了灰度图像的反色方案不能直接使用已有的全黑反色PBVCS来构造的原因和存在的问题,进而给出一般灰度图像的反色(k,n)-VCS,该方案的有效性被证明,使用我们的灰度反色VCS,对分存图执行有限次反色和叠加操作可正确重构密图。     

基于随机栅格的异或区域递增式视觉密码方案

针对现有区域递增式视觉密码方案仅局限于或运算,导致秘密图像中白像素无法被正确恢复的问题,给出了基于异或运算的区域递增式视觉密码的定义.通过迭代基于随机栅格的(k,k)单秘密视觉密码方案,利用0是异或{0,1}群中单位元的特性,设计了适用于异或运算的(k,n)单秘密方案的共享份生成算法,并构造了(k,n)区域递增式方案的秘密分享与恢复流程,分享过程中对于原像素s,依据s所在区域的密级,通过随机选取一个授权子集Q对s重新赋值,并利用(k,n)单秘密方案完成像素加密.恢复过程同一般视觉密码方案相同,最后对方案的有效性进行了理论证明.实验结果表明,该方案不仅实现了像素不扩展,且所有共享份叠加时白像素可以完美恢复.     

Visual multiple-secret sharing for flexible general access structure by random grids

For visual secret sharing (VSS), general access structure (GAS), which can freely define the qualified set and the forbidden set, provides dealers the ability to share secret information with the qualified set but not the forbidden set. In previous studies, the proposed GAS schemes have focused on strong GAS, but it has retained restrictions and inconvenience in some secret-sharing scenarios. Recently, the random-grid-based VSS (RG-based VSS) technique has aimed to overcome the problem of pixel expansion from which the visual-cryptography-based VSS (VC-based VSS) techniques usually suffer. This paper presents a flexible GAS VSS scheme by RG that is appropriate for wide use and that serves special cases like (2, n), (n, n), and (k, n). The paper also outlines how the scheme can be extended for multiple secrets. The performance and the security of the scheme are theoretically analyzed.     

A new visual cryptography with multi-level encoding

Visual secret sharing (VSS) is a visual cryptography scheme which decodes secret messages into several enlarged shares, and distributes them to different participants. The participants can recover the secret messages by stacking their shares, and then secret message can be revealed by human visual sensitivity. Afterward some researchers start to research size invariant scheme, and apply to encode grayscale images such as scenic photos or pictures, not only binary messages. Owing to the gray values distribution of pictures are different, extreme distribution may cause blurred revealed image. In this paper, we proposed a size invariant VSS scheme which is suitable for different distribution of image's gray values. Experiment results show that the reconstructed images of our method, for brighter, darker, and normal images, have clearer and higher contrast, and without apparent artifact and unexpected contour.