非等量备份和双认证自修复有限域图像分存

传统有意义图像分存方案存在认证能力偏低、攻击后不具备修复能力或修复能力整体较弱以及嵌入掩体视觉质量不高等问题.针对以上问题,提出一种结合非等量备份和双认证自修复有限域图像分存方案.所提方案包含分存和恢复阶段.在分存阶段,首先对密图做1级离散小波变换,取LL子带按密钥置乱,并对置乱后LL子带每个系数比特按比特位重要程度分组进行非等量备份来构造与密图等大备份图;然后对密图和备份图每个像素及其对应7K-13位认证信息在GF（2⁷）有限域进行（K,N）分存,将产生的7位分存信息和使用密钥产生的1位认证信息使用优化LSB法嵌入到N个掩体2×2分块中;最后对密钥进行（K,N）分存,将子密钥对应MD5值公开到第3方公信方并将子密钥和嵌入掩体分发给参与者.在恢复阶段,首先对参与者提供的子密钥真实性进行检验,利用检验通过子密钥对密钥进行恢复;其次对分发掩体2×2分块嵌入的分存信息和1位认证信息使用密钥进行第1重认证,利用第1重认证通过分存信息重建GF（2⁷）有限域分存多项式,提取出密图和备份图每个像素及其对应的7K-13位认证信息并对其进行第2重检验和构造初步密图、备份图以及认证图;再次由备份图和认证图重构密图LL子带,然后对其做逆置乱和逆离散小波变换得到密图修复参考图;最后对认证图每一个认证不通过秘密像素,根据其周围像素认证情况选择多项式插值拟合或进行修复参考图像素替代修复.理论和实验表明,同现有方法相比,所提方法具备更好认证能力,并能充分使用双认证和自然图像邻近像素相关性来提升其攻击后修复能力,且分发掩体具备较高视觉质量.     

结合EMD-cl嵌入的多载体密图分存方法

目的 传统误差扩散或恢复函数的多载体密图分存会对嵌密载体视觉质量造成较大影响,同时恢复函数需单独设计,只适用于二值或灰度图像,且通过简单Arnold置乱或异或加密仅能提供有限的安全性。针对此问题,提出结合EMD-c^l嵌入的多载体密图分存方法。方法 采用双哈希MD5和SHA-1值产生多组与密图属性和用户密钥有关的置乱参数,驱动2维双尺度矩形映射来改变载体像素对应关系,然后将置乱后载体同位置像素构成向量,按扩展约瑟夫遍历映射分配基向量,通过EMD-c^l嵌入秘密像素,从而将密图分存到多张载体中。结果 采用EMD-c^l提高了嵌密载体视觉质量且不需额外设计恢复函数,可针对不同分辨率和灰度阶密图分存。所提方法载体像素位置和EMD-c^l基向量都与密图MD5和SHA-1值以及用户密钥紧密绑定,仅有正确用户密钥和密图MD5和SHA-1值才能对密图恢复,并可通过第三方公信方托管的参与者分存信息MD5和SHA-1值使得所述策略具备认证能力。所提方法密钥空间为1.193 6×10¹¹⁸,可抵抗暴力破解。实验结果表明,结合EMD-c^l,所提方法具有较好的嵌密载体视觉质量,NC趋近于1,对于EMD-3^l,嵌密载体PSNR均接近50 dB;对于EMD-5^l和EMD-7^l,PSNR分别达到45 dB和42 dB,而传统方法,PSNR最好仅为42 dB。所提方法可分存不同分辨率和灰度阶密图,可对参与者密钥分存信息的真实性进行检验且对密图哈希和用户密钥极度敏感。结论 所提方法具有较低复杂度,较高安全性和普适性及认证能力,在整体性能上优于传统误差扩散或恢复函数的多载体密图分存方法,适用于对嵌密载体视觉质量要求高和针对不同分辨率和灰度阶密图分存的安全场景中。     

一种基于GF(23)的(K,N)有意义无扩张图像分存方案

传统有意义图像分存存在像素扩张,通常只对分存信息以较短的认证信息进行甄别,从而导致重构的秘密像素真实性无法准确鉴别。针对此问题,提出一种基于GF(2³)的(K,N)有意义无扩张图像分存方案。在该方案中,首先生成加密映射表并利用秘密像素的位置信息对秘密像素进行加密;然后将秘密像素的认证信息和加密像素在GF(2³)有限域下进行(K,N)分存,嵌入到掩体图像对应的像素中;最后将映射表的生成密钥进行(K,N)分存,计算每个子密钥的MD5值并公布到第3方公信方以防止掩体图像持有者作弊。实验结果表明,所提方案能准确地识别出秘密图像攻击区域,不存在任何像素扩张,掩体图像与秘密图像等大且嵌入分存信息的掩体图像具有较好的视觉质量。     

光RP(k)网络上Hypercube通信模式的波长指派算法

波长指派是光网络设计的基本问题,设计波长指派算法是洞察光网络通信能力的基本方法.基于光RP(k)网络,讨论了其波长指派问题. 含有N=2ⁿ个节点的Hypercube通信模式,构造了节点间的一种排列次序Xn,并设计了RP(k)网络上的波长指派算法.在构造该算法的过程中,得到了在环网络上实现n维Hypercube通信模式的波长指派算法.这两个算法具有较高的嵌入效率.在RP(k)网络上,实现Hypercube通信模式需要max{2,「5(2^n-5/3」}个波长.而在环网络上,实现该通信模式需要复用(N/3+N/12(个波长,比已有算法需要复用「N/3+N/4」个波长有较大的改进.这两个算法对于光网络的设计具有较大的指导价值.     

基于熵加权K-means全局信息聚类的高光谱图像分类

目的 高光谱图像波段数目巨大，导致在解译及分类过程中出现“维数灾难”的现象。针对该问题，在K-means聚类算法基础上，考虑各个波段对不同聚类的重要程度，同时顾及类间信息，提出一种基于熵加权K-means全局信息聚类的高光谱图像分类算法。方法 首先，引入波段权重，用来刻画各个波段对不同聚类的重要程度，并定义熵信息测度表达该权重。其次，为避免局部最优聚类，引入类间距离测度实现全局最优聚类。最后，将上述两类测度引入K-means聚类目标函数，通过最小化目标函数得到最优分类结果。结果 为了验证提出的高光谱图像分类方法的有效性，对Salinas高光谱图像和Pavia University高光谱图像标准图中的地物类别根据其光谱反射率差异程度进行合并，将合并后的标准图作为新的标准分类图。分别采用本文算法和传统K-means算法对Salinas高光谱图像和Pavia University高光谱图像进行实验，并定性、定量地评价和分析了实验结果。对于图像中合并后的地物类别，光谱反射率差异程度大，从视觉上看，本文算法较传统K-means算法有更好的分类结果；从分类精度看，本文算法的总精度分别为92.20%和82.96%， K-means算法的总精度分别为83.39%和67.06%，较K-means算法增长8.81%和15.9%。结论 提出一种基于熵加权K-means全局信息聚类的高光谱图像分类算法，实验结果表明，本文算法对高光谱图像中具有不同光谱反射率差异程度的各类地物目标均能取得很好的分类结果。     

结合纹理梯度抑制与L0梯度最小化的纹理滤波

目的 纹理滤波是计算机视觉领域的一个基础应用工具,其目标是抑制图像中不必要的纹理细节和保持图像的主要结构。目前已有的纹理滤波方法多存在强梯度纹理无法被抑制或结构丢失的问题,为此提出一种结合纹理梯度抑制与L₀梯度最小化的纹理滤波算法。方法 首先,提出一种能够区分结构/纹理像素的方向性区间梯度算子,其中采取了局部对比度拉伸和尺度自适应策略,提升了弱梯度结构像素的识别能力。随后,利用区间梯度幅值对原始图像梯度进行抑制,并用抑制后的图像梯度进行图像重建,获得纹理像素梯度小于结构像素梯度的纹理抑制图像。最后,考虑到纹理梯度抑制时会对结构像素的梯度产生一定的衰减作用,本文采用具有梯度提升作用的L₀梯度最小化方法对纹理抑制图像进行滤波,得到纹理抑制结构保持的纹理滤波图像。结果 通过测试马赛克和自然风景等不同类型的图片,并与L₀梯度最小化、滚动引导图像滤波、相对总变分、共现滤波等方法相比较,本文算法能够在抑制强梯度纹理的情况下对图像的主要结构得以保持,并且具有良好的普适性和鲁棒性。同时本文将纹理滤波应用于图像的边缘检测和细节增强,取得了不错的效果提升。结论 本文算法在兼顾强梯度纹理的抑制和结构的保持方面已超越已有的方法,对于图像的目标识别、图像融合、边缘检测等易受强梯度纹理干扰的技术领域,具有较大的应用潜力。     

一种基于K-Means局部最优性的高效聚类算法

K-Means聚类算法只能保证收敛到局部最优,从而导致聚类结果对初始代表点的选择非常敏感.许多研究工作都着力于降低这种敏感性.然而,K-Means的局部最优和结果敏感性却构成了K-MeanSCAN聚类算法的基础.K-MeanSCAN算法对数据集进行多次采样和K-Means预聚类以产生多组不同的聚类结果,来自不同聚类结果的子簇之间必然会存在交集.算法的核心思想是,利用这些交集构造出关于子簇的加权连通图,并根据连通性合并子簇.理论和实验证明,K-MeanScan算法可以在很大程度上提高聚类结果的质量和算法的效率.     

Multi-log2N交换网络的性能分析模型及控制算法

高速多平面交换网络解决了其内部冲突问题,但需要相应的路由控制算法的辅助,否则,内部冲突不能彻底解决.这是因为包在输入级路由平面的选择不够恰当,容易导致路由冲突的产生.因此,根据冲突链路集的思想,给出一种Multi-log₂N交换网络的控制算法.该算法控制分组在路由平面间的选择,不仅能够适用于RNB和SNB,还能实现单播和多播的控制,保障Multi-log₂N完全实现无阻塞.另一方面,Multi-log₂N消除了内部的链路冲突,提高了交换速率,但对其交换性能缺乏系统的理论分析.给出一种基于嵌入式马尔可夫链的分析模型,对Multi-log₂N网络中队列的使用及分组在队列中的平均等待时间、平均队长等相关性能指标进行了系统的分析,为基于Multi-log₂N的光交换节点的设计提供了良好的理论依据.     

完全析取范式群判定SHOIN(D)-可满足性

针对非循环概念提出了一种对SHOIN(D)-概念可满足性进行判断的方法——CDNF(complete disjunctive normal form)算法.该算法通过把非循环定义的概念描述本身构建成分层次的析取范式群,并通过子句重用技术阻止无谓的子概念扩展,这样的析取范式群具有可满足性自明性,从而可以实现对SHOIN(D)-概念可满足性的直接判断.该算法基本上消除了判断过程中描述重复的现象,从而在空间、时间性能上都比Tableau算法有更好的表现.     

P2-Packing问题参数算法的改进

P₂-Packing问题是一个典型的NP难问题.目前这个问题的最好结果是时间复杂度为O^*(2^5.301k)的参数算法,其核的大小为15k.通过对P₂-packing问题的结构作进一步分析,提出了改进的核心化算法,得到大小为7k的核,并在此基础上提出了一种时间复杂度为O^*(2^4.142k)的参数算法,大幅度改进了目前文献中的最好结果.     

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.     

Secret image sharing based on cellular automata and steganography

Recently Lin and Tsai [Secret image sharing with steganography and authentication, The Journal of Systems and Software 73 (2004) 405-414] and Yang et al. [Improvements of image sharing with steganography and authentication, The Journal of Systems and Software 80 (2007) 1070-1076] proposed secret image sharing schemes combining steganography and authentication based on Shamir's polynomials. The schemes divide a secret image into some shadows which are then embedded in cover images in order to produce stego images for distributing among participants. To achieve better authentication ability Chang et al. [Sharing secrets in stego images with authentication, Pattern Recognition 41 (2008) 3130-3137] proposed in 2008 an improved scheme which enhances the visual quality of the stego images as well and the probability of successful verification for a fake stego block is 1/16.In this paper, we employ linear cellular automata, digital signatures, and hash functions to propose a novel (t,n)-threshold image sharing scheme with steganographic properties in which a double authentication mechanism is introduced which can detect tampering with probability 255/256. Employing cellular automata instead of Shamir's polynomials not only improves computational complexity from to O(n) but obviates the need to modify pixels of cover images unnecessarily. Compared to previous methods [C. Lin, W. Tsai, Secret image sharing with steganography and authentication, The Journal of Systems and Software 73 (2004) 405-414; C. Yang, T. Chen, K. Yu, C. Wang, Improvements of image sharing with steganography and authentication, The Journal of Systems and Software 80 (2007) 1070-1076; C. Chang, Y. Hsieh, C. Lin, Sharing secrets in stego images with authentication, Pattern Recognition 41 (2008) 3130-3137], we use fewer number of bits in each pixel of cover images for embedding data so that a better visual quality is guaranteed. We further present some experimental results.     

Reversible secret image sharing scheme in encrypted images

The previous secret image sharing schemes did not provide a copyright and privacy for cover images. The reason is that a dealer selects a cover image by itself and embeds directly the secret data into the cover image. In this paper, a reversible secret image sharing scheme in encrypted images is proposed in order to provide the copyright and privacy of the cover image. We divide a role of the dealer into an image provider and a data hider. The image provider encrypts the cover image and transmits the encrypted image to the data hider, and the standard stream cipher as one-time pad (OTP) with a random secret key is used. The data hider embeds the secret data into the encrypted image, and the encrypted shadow images are transmitted to the corresponding participant. We utilize the polynomial arithmetic operation over GF(2⁸) during the sharing of the encrypted shadow images, and the coefficient of the highest-order term is fixed to one in order to prevent the overflow and the security problem. In the reconstruction procedure, the secret data can be extracted and the cover image can be reconstructed exactly from t or more encrypted shadow images with Lagrange interpolation. In experimental results, the proposed method shows that the PSNR is sustained close to 44 dB regardless of the embedding capacity, where the embedding capacity is 524,288 bits on average.     

A novel (n,t, n) secret image sharing scheme without a trusted third party

Secret image sharing is a technique to share a secret image among a set of n participants. A trusted third party embeds the secret image into the cover image to generate shadow images such that at least t or more shadow images can reconstruct the secret image. In this paper, we consider an extreme and real-world situation, in which there is no one who is trusted by anyone else. In the proposed scheme, the participants can act as a dealer and communicate with each other in a secret channel. Each participant can generate her/his own shadow image independently, according to the cover image and the secret image. Experimental results are provided to show that the shadow images have satisfactory quality. In addition, our scheme has a large embedding capacity, and the secret image can be reconstructed losslessly.     

A secure image sharing scheme with high quality stego-images based on steganography

Image sharing can be utilized to protect important commercial, military or private images against a single point of failure. Many existing image sharing schemes may have one or more of the security weaknesses as follows: First, noise-like image shares may easily arouse the attackers’ attention; Second, cheating in the recovery of the secret image cannot be prevented effectively; Third, the requisite size of cover images may be very large; Finally, poor quality of the stego-images may lessen camouflage effects. In this paper, a novel secure image sharing scheme with high quality stego-images is proposed. With the use of LOCO-I compression as a preprocessing approach, the statistical correlations between neighboring pixels of a secret image drop significantly, which may greatly enhance the visual security of the proposed scheme. And the necessary size of cover images is reduced. Moreover, the PSNR values of stego-images are much higher than the related works. In order to detect three kinds of deception during secret image reconstruction, the hash-based message authentication codes of an image share, the value of argument x and the identity ID of a participant are embedded into a cover image together with the image share. In addition, the application of dynamic embedding with a random strategy further enhance the security of our scheme.     

Priority visual secret sharing of random grids for threshold access structures

Conventional (k, n)-threshold visual secret sharing of random grids (VSSRG) schemes generate n shares having the same average light transmission from a secret image to be shared, and any information related to the secret image cannot be identified externally from a single share held by one participant. In addition, the secret image can be recovered only by collecting k shares individually held by participants, and every share has the same capability of recovering the secret image. In fact, participants’ priority levels vary in certain conditions, and therefore their shares’ capabilities to recover the secret image are different. The priority-based (k, n)-threshold VSSRG scheme proposed in this study enables the assignment of different priority weights to each share to create different priority levels. During decryption, the stacking of shares with different priority levels recovers the secret image at different levels. Moreover, shares individually held by each participant have the same average light transmission, and consequently the shares’ priority levels cannot be identified externally.     

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.     

Sharing secrets in stego images with authentication

Recently, Lin and Tsai and Yang et al. proposed secret image sharing schemes with steganography and authentication, which divide a secret image into the shadows and embed the produced shadows in the cover images to form the stego images so as to be transmitted to authorized recipients securely. In addition, these schemes also involve their authentication mechanisms to verify the integrity of the stego images such that the secret image can be restored correctly. Unfortunately, these schemes still have two shortcomings. One is that the weak authentication cannot well protect the integrity of the stego images, so the secret image cannot be recovered completely. The other shortcoming is that the visual quality of the stego images is not good enough. To overcome such drawbacks, in this paper, we propose a novel secret image sharing scheme combining steganography and authentication based on Chinese remainder theorem (CRT). The proposed scheme not only improves the authentication ability but also enhances the visual quality of the stego images. The experimental results show that the proposed scheme is superior to the previously existing methods.     

A lightweight authenticable visual secret sharing scheme based on turtle shell structure matrix

This paper proposes a novel visual secret sharing scheme based on a turtle shell structure matrix (TSSM) with reversibility and lightweight authentication. With the assistance of TSSM, the secret data is embedded into the original cover image and three meaningful shadow images are generated. To increase the image quality of the generated shadows, the proposed scheme designs an embedding structure that will be used to embed a secret image into shadows based on the TSSM, rather than by directly embedding authentication codes. The designed embedding structure offers a robust authentication capability at the cost of lightweight computation. Moreover, the hidden secret data can be extracted completely and the cover image can be restored losslessly through the collaboration of the three received shadows. Experimental results, on various grayscale test images, confirmed that our proposed scheme provides high visual quality and excellent authentication.