Multiuser-based shadow watermark extraction system

A new watermarking scheme having the ability of sharing secret with multi-users is proposed. It splits the original watermark into two shares and embeds one share into the cover image to increase the security. A polarization procedure is performed to establish a polarity stream from the cover image. The second share and the polarity stream are used to generate a master key and several normal keys. In this system, only the super-user can reveal the genuine watermark directly. Other users possess the normal keys can obtain shadow watermarks merely. By combining the shadow watermarks together, the real watermark can be recovered.     

Secret image sharing with steganography and authentication

A novel approach to secret image sharing based on a (k,n)-threshold scheme with the additional capabilities of steganography and authentication is proposed. A secret image is first processed into n shares which are then hidden in n user-selected camouflage images. It is suggested to select these camouflage images to contain well-known contents, like famous character images, well-known scene pictures, etc., to increase the steganographic effect for the security protection purpose. Furthermore, an image watermarking technique is employed to embed fragile watermark signals into the camouflage images by the use of parity-bit checking, thus providing the capability of authenticating the fidelity of each processed camouflage image, called a stego-image. During the secret image recovery process, each stego-image brought by a participant is first verified for its fidelity by checking the consistency of the parity conditions found in the image pixels. This helps to prevent the participant from incidental or intentional provision of a false or tampered stego-image. The recovery process is stopped if any abnormal stego-image is found. Otherwise, the secret image is recovered from k or more authenticated stego-images. Some effective techniques for handling large images as well as for enhancing security protection are employed, including pixelwise processing of the secret image in secret sharing, use of parts of camouflage images as share components, adoption of prime-number modular arithmetic, truncation of large image pixel values, randomization of parity check policies, etc. Consequently, the proposed scheme as a whole offers a high secure and effective mechanism for secret image sharing that is not found in existing secret image sharing methods. Good experimental results proving the feasibility of the proposed approach are also included.     

基于BTC与秘密共享的图像水印算法

结合块截短编码与秘密共享,提出一种新的鲁棒图像水印算法。该算法利用BTC编码由原图像构建特征共享,利用水印图像与特征共享一起生成私有共享。由待验证图像构建的特征共享与私有共享一起恢复水印图像。私有共享的生成与特征共享有关,可实现对同一图像的多水印注册。特征共享的稳健性确保了算法的水印鲁棒性,水印嵌入没有引起图像质量的改变。实验结果表明该算法对一般信号处理攻击有较高的鲁棒性。     

用于图像认证的变容量恢复水印算法

兼顾水印嵌入容量和安全性,提出一种水印容量可变的数字图像可恢复水印算法.该算法提取2×2图像块特征生成变容量恢复水印——平滑块6比特,纹理块12比特.图像块的恢复水印基于密钥随机嵌入在其它图像块的低有效位,通过比较图像块特征与相应恢复水印重构的块特征并结合邻域特征判定图像块的真实性,变容量恢复水印用尽可能少的比特数保存足够的图像块信息,仅被嵌入一次且同时用于篡改检测与恢复,不仅有效降低了水印嵌入容量,而且提高了算法抵抗恒均值攻击的能力.实验仿真结果表明,该算法得到的含水印图像和恢复图像的质量好,且能有效抵抗拼贴攻击、恒均值攻击等已知伪造攻击.     

一种高效的(t,n)门限可视密码方案

首先提出了一种多秘密共享方案,该方案共享t个多重秘密,需要计算t个联立方程。然后基于多秘密共享的思想,提出了一种新的(t,n)门限可视密码方案。该方案把一幅秘密图像分割成t幅子秘密图像,每幅子秘密图像是原始图像的1/t;然后再由t幅子秘密图像计算出n幅共享图像,秘密送给n个参与者,其中每个共享图像与子秘密图像同样大小。使得任意t个或更多的参与者合作能够恢复原始秘密图像,而任意少于t个参与者却得不到有关原始图像的任何信息。另外,恢复的图像和秘密图像完全一样,没有任何失真。新方案安全、有效,是一种完备的(t,n)门限方案,适用于把黑白、灰度、彩色图像作为秘密进行共享。     

基于整数小波变换的医学图像易碎水印方法

为了对医学图像进行快速鲁棒的认证提出了一种基于整数小波变换的易碎水印算法.该算法首先利用小波分解后的四叉树结构结合树节点上的统计信息和密钥来选择嵌入水印的位置,然后对确定嵌入水印的位置只嵌入1bit的水印信息.该算法具有以下特点：（1）图像嵌入水印后具有较高的信噪比,适用于医学图像的认证;（2）结合小波系数的统计信息来选择嵌入水印的位置,可保证水印的易碎性;（3）小波分解在空频域的特性使得算法对篡改有很强的定位能力;（4）可利用密钥对本算法进行保护,即使算法公开,也能抵挡恶意攻击.实验结果表明,该算法适用于医学图像的认证,并且复杂度较低,实用性较强.     

An image copyright protection scheme by encrypting secret data with the host image

In this paper, a zero-watermarking based copyright protection scheme is proposed. The secret watermark image is not embedded in the host image rather it is encrypted with the host image. The proposed scheme is making use of discrete cosine transform and singular value decomposition to extract robust features of the host image. Further the selected robust features are used to encrypt the secret image. The secret image is encrypted with the host image by generating two shares namely master share and ownership share. The master share is generated by differential classification of features extracted. The ownership share is generated with the help of master share and the secret image. The two shares separately don’t give any clue of the secret image but when stacked together the encrypted secret image is revealed. Experimental study is conducted to evaluate the robustness of the algorithm against various signal processing and geometrical attacks.     

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.     

一种基于秘密共享方案的数字图像水印算法

提出了一种新的基于秘密共享方案的数字图像水印算法,其主要特点是将原始水印分成两份,一份嵌入载体图像增加系统安全性.通过载体图像生成一个辅助矩阵(极性矩阵),第二份和极性矩阵用来产生一个主密钥和若干个普通密钥.在此系统中,只有拥有主密钥的用户才能直接恢复出真正的水印,其他拥有普通密钥的用户只能恢复阴影水印,将那些阴影水印联合起来,才能恢复出真正的水印,所以算法具有一定的实用价值.实验结果证明:所提出的水印算法对JPEG压缩、椒盐噪声、剪切等图像处理攻击具有很好的鲁棒性.     

A (2, 2) Visual Cryptography Technique with Improved Contrast

ABSTRACT

Visual cryptography is a technique used to share a secret among many participants. The problem with visual cryptography technique is that the secret is not perfectly recovered, i.e. a black secret pixel is perfectly recovered but a white secret pixel is recovered with less contrast. Because of this, the overall quality of recovered secret is poor. So to improve the quality of recovered secret image, we need to improve the contrast. In this paper, we have proposed a (2, 2) visual cryptography technique with improved contrast as compared to the traditional (2, 2) visual cryptography scheme (VCS). In the proposed technique, we have used additional basis matrices for encrypting the secret pixels. The quality of the recovered secret image is compared with traditional (2, 2) VCS using various image quality metrics.     

一种新的彩色可视秘密共享方案

提出了一种基于线性方程组求解的彩色可视秘密共享方案。该方案把一幅图像秘密地分成n幅共享图像,使得任意k个或更多的共享能够恢复秘密图像,而任意少于k个共享却得不到有关原始图像的任意信息。另外,每个共享图像与原始图像有着同样大小,而且恢复图像和秘密图像完全一样,没有任何失真。所以它是一种理想、完备的（k,n）门限方案,适用于把黑白、灰度、彩色图像作为秘密进行共享。     

Progressive sharing for a secret image

Based on the wavelet transform, a new progressive sharing scheme is proposed to share a secret image into several shadow images using SPIHT encoding processes and Shamir’s threshold scheme. Quality refinement of the recovered image is achieved by the data consumed from the threshold number (r) of shadow images and each single shadow image reveals no information about the secret image. The size of each shadow image is smaller than 1/r of the secret image and any number of shadow images that is less than r reveals no information about the secret image. The proposed approach is secure for image sharing and provides excellent peak signal-to-noise ratio (PSNR) versus rate performance. Experimental results have demonstrated the promising performance of this method in progressive sharing.     

基于伪随机数的数字水印

针对密码技术在数据保护方面的不足,提出一种新的数字水印算法——基于分块统计的水印嵌入算法。采用Logistic混沌序列发生器和m序列发生器产生伪随机数序列,将包含信息量较少、安全性要求较高的二值秘密图像嵌入载体图像。测试证明,该方法能使水印图像具有较高的信噪比,可完整方便地恢复出秘密图像。     

A hybrid DWT-SVD copyright protection scheme based on k-means clustering and visual cryptography

In this paper, a novel copyright protection scheme that combines the discrete wavelet transform (DWT) and the singular value decomposition (SVD) is proposed. Instead of modifying the original host image to conceal a secret image, the proposed scheme first extracts the image features from the host image by applying the DWT and the SVD. The extracted features are then classified into two clusters by employing the k-means clustering technique, and a master share is generated using the clustering result. Finally, the master share is used together with a secret image to construct an ownership share according to a two-out-of-two visual cryptography (VC) technique. When rightful ownership needs to be determined, the secret image for ownership identification can be revealed by stacking the master share and the ownership share. Experimental results demonstrate that the proposed scheme can effectively resist several common attacks. In addition, the revealed watermark can be easily recognized by human eyes, even if the host image has undergone severe attacks.     

一种基于矢量共享方案的DCT域上数字水印分存算法

数字水印分存是将秘密共享的思想用于数字水印，将原始水印信息分解成n份分存水印信息，获得其中部分分存水印信息就能恢复出原始水印信息．该文提出一种基于矢量共享方案的DCT域上的数字水印分存算法．它将矢量共享的思想用于数字水印．原始载体图像分块后，在DCT变换的低频域上加载分存后的水印数据．水印信息隐藏前，对原始水印和分块水印都进行扰乱处理，同时分存也具有加密作用．算法具有很高的安全性和较好的稳健性．实验表明，算法还具有较好的隐藏效果和很好的抗剪切、抗压缩等功能．     

结合调整差值变换的(K,N)有意义图像分存方案

目的 针对传统有意义分存方法存在的像素扩张和分发掩体图像视觉质量不高等问题,提出一种结合调整差值变换的(K,N)有意义图像分存方案,该方案可用于与掩体等大且同为自然图像的密图分存.方法 在分存阶段,首先用调整差值变换将密图转换为差值图和位置图;其次将差值图和位置图进行(K,N)分存,分别嵌入到掩体图像中,并使用密钥确定位置图分存信息的嵌入位置和根据位置图中不同的差值类型选择不同的差值嵌入方法;再次对密钥进行(K,N)分存,将子密钥和分发掩体对应的MD5值公布到第3方公信方作为认证码;最后将子密钥和分发掩体分发给参与者进行保管.在恢复阶段,首先核对参与者的子密钥和分发掩体对应的MD5值,若认证通过的人数小于K,则恢复失败;否则,使用认证通过的子密钥还原出密钥,然后根据密钥提取并恢复出位置图;其次根据位置图中的差值类型来提取和恢复出差值图;最后使用逆调整差值变换还原出最终密图.结果 同现有方法相比,所提策略不存在像素扩张且分发掩体图像视觉质量较高,具有较强的恶意参与者检测能力.结论 本文方法的掩体图像与密图等大且同为自然图像,同经典有意义图像分存方案相比,克服了像素扩张问题,嵌入信息后的掩体图像具有较高的视觉质量,使用第3方公信方存储的MD5值作为认证码,具有较强的恶意参与者识别能力.     

Reversible secret-image sharing with high visual quality

This paper proposes a reversible secret-image sharing scheme for sharing a secret image among 2n shadow images with high visual quality (i.e., they are visually indistinguishable from their original images, respectively). In the proposed scheme, not only can the secret image be completely revealed, but the original cover images can also be losslessly recovered. A difference value between neighboring pixels in a secret image is shared by 2n pixels in 2n shadow images, respectively, where n?≥?1. A pair of shadow images which are constructed from the same cover image are called brother stego-images. To decrease pixel values changed in shadow images, each pair of brother stego-images is assigned a weighted factor when calculating difference values to be shared. A pixel in a cover image is recovered by calculating the average of corresponding pixels in its brother stego-images. A single stego-image reveals nothing and a pair of pixels in brother stego-images reveals partial difference value between neighboring secret pixels. The more brother stego-images are collected, the more information in the secret image will be revealed. Finally, a secret image will be completely revealed if all of its brother stego-images are collected.     

Random-grid based progressive visual secret sharing scheme with adaptive priority

This paper describes a random-grid-based progressive visual secret sharing scheme, wherein the priority weighting of each share can be adjusted. In this scheme, shares are recovered progressively to obtain a secret image. Therefore, with increasing number of shares that are collected, more information of the secret image is recovered, and vice versa. In addition, each user participating in the secret sharing can adjust the priority weighting of a share based on their determined level of secrecy; thus, each share generated by the proposed scheme has a different priority weighting value. During decryption, depending on the priority weightings of the stacked shares, the secret image can be recovered to different extents. Further, the priority level of these shares cannot be distinguished based on the average light transmission of the reconstructed image, thereby guaranteeing high security.     

一类基于奇异值分解的图像水印算法伪验证分析

通过分析发现,一类基于奇异值分解的图像水印算法存在致命漏洞,即利用在水印嵌入过程中生成的密钥可以从其他图像（含未嵌入水印的图像）中提取出高相关的水印信息,称这一新发现的算法漏洞为水印算法的伪验证,并由此首次提出了水印算法伪验证的定义和判定条件。然后通过实例分析,指出基于奇异值分解的水印算法之所以存在伪验证,是由于奇异值分解使得水印信息主要包含于正交阵U、V中,因此水印的提取与正交阵U、V以及奇异值的分布类型有关,而与奇异值的具体取值无关。     

一种二值图像的阈值可视密码方案

目前提出的许多关于二值可视密码方案的论文都致力于研究在可视秘密共享方案里如何使像素扩展比较小或恢复图像的对比度比较高的问题。基于Shamir的秘密共享方案的思想,提出一种新的二值图像（k,n）-VCS可视密码方案。该方案利用二元域上线性方程组解的特征及多层（k,k）-VCS构造基础矩阵S⁰,S¹,给出一个强的访问结构,从而获得（k,n）-VCS可视密码方案更小的像素扩展。