Scalable user-friendly image sharing

Image sharing addresses a fault-tolerant protection mechanism for important images. In a typical image sharing scheme, the generated shadow images usually have a noise-like appearance that conceals the secret image completely, but this makes them difficult to identify and manage. This paper proposes a scalable user-friendly image sharing scheme in which each generated shadow image looks like a shrunken replica of the original image. The scheme provides an easy-to-identify interface for managing the shadow images. Compared with previous user-friendly image sharing schemes, the proposed method can reconstruct the original image without any loss and still has the small-size shadow images. A notable feature is that the qualities of generated shadow images are scalable in the proposed scheme, which allows the quality of the shadow images to be adjusted according to the requirements of diverse applications.     

Sharing more information in gray visual cryptography scheme

Visual cryptography scheme (VCS) shares a binary secret image into several binary shadows, and the secret image can be visually revealed by stacking qualified shadows without computation. From the point of view of sharing secret information, VCS is not efficiency because of the large size expansion and low visual quality. In this paper, we introduce a general gray visual cryptography scheme, which can share more information, called Sharing More Information Gray Visual Cryptography Scheme (SMIGVCS). All the shadow pixels of VCS embed additional information to generate gray shadows of SMIGVCS, and the embedded information comes from the shadows of a polynomial-based secret sharing scheme (PSSS). In the revealing process, a vague secret image is visually decoded by stacking qualified shadows, and more information is revealed by computation. Compared with the two-in-one image secret sharing scheme (TiOISSS), our SMIGVCS can achieve smaller shadow size with acceptable visual quality.     

Scalable secret image sharing

In this paper, we propose an innovative scheme, namely the scalable secret image sharing scheme, for sharing an image O among n participants such that the clarity of the reconstructed image (i.e., the amount of information therein) scales with proportion with the number of the participants. The proposed scheme encodes O into n shadow images that exhibit the following features: (a) each shadow image reveals no information about O, (b) each shadow image is only half the size of O, (c) any k (2⩽k⩽n) shadow images can be used to reconstruct O in a scalable manner such that the amount of information about O is proportional to k, and (d) O can be reconstructed perfectly when all of the n shadow images are available. The clarity of O can be measured in terms of several metrics. We define three modes, namely the multisecret, priority, and progressive modes, for sharing O in our scheme. The scalability and flexibility of the proposed schemes indicate the wide range of potential applications for secret image sharing.     

Quadri-directional searching algorithm for secret image sharing using meaningful shadows

Contrary to conventional protecting data such as cryptographic techniques which encrypt the data with a secret key, secret sharing takes an approach to ensure well protection of transmitted information by allowing a secret message M to be divided into n pieces. Secret message M can be held by n participants to avoid the secret from incidentally or intentionally being lost. In a secret sharing scheme, secret information leaks from shadows, attack on shadow image, and large shadow image issues which has arisen when developing an algorithm. Although existing algorithms provide remedies for such problems, the computational complexity of existing algorithms is still questionable. Therefore, we propose a low computational complexity Quadri-Directional Searching Algorithm (QDSA) for secret image sharing. Experiment results show that the proposed algorithm ensures that generated shares are of high quality and no secret information is leaked from these shares, thus it guarantees high security of our scheme.     

A Novel （n, n） Secret Image Sharing Scheme Based on Sudoku

Recently, Chang et al. proposed a Sudoku-based secret image sharing scheme. They utilized the Sudoku grid to generate meaningful shadow images, and their scheme satisfied all essential requirements. Based on Chang et al.'s scheme, we propose a novel (n, n) secret image sharing scheme based on Sudoku. In the proposed scheme, a secret image can be shared among n different cover images by generating n shadow images, and the secret image can be reconstructed without distortion using only these n shadow images. Also, the proposed scheme can solve the overflow and underflow problems. The experimental results show that the visual quality of the shadow images is satisfactory. Furthermore, the proposed scheme allows for a large embedding capacity.     

基于马赛克技术的秘密图像共享

在传统的秘密图像共享算法中,通常产生类似噪声的影子图像,极易引起攻击者的注意。针对这一问题,文中根据马赛克技术提出了一种产生有意义的影子图像算法。通过图像相似度的比较,可将秘密图像共享到载体图像中,得到含有秘密图像信息的马赛克图像。然后采用可逆信息隐藏的技术将图像块的位置序列隐藏到马赛克图像中,得到完整的影子图像。通过文中所提算法产生的影子图像,既可避免攻击者的注意又能恢复出无损的秘密图像。     

多重门限的图像秘密共享方案

 针对传统的基于视觉密码的图像秘密共享方案存在像素扩张导致其只能共享小尺寸的秘密图像、信息隐藏效率较低的问题,提出一种能够提高信息隐藏容量的(t,k,n)多重门限图像秘密共享方案.该方案利用秘密图像信息控制视觉密码方案中共享矩阵的选取,从而实现秘密图像在视觉密码方案中的隐藏.在秘密图像恢复的第一阶段,任意t个参与者直接叠加其影子图像后可以视觉解密出低质量的秘密图像信息;在第二阶段,任意k个参与者可以从影子图像中提取出隐藏的信息,并通过计算恢复出精确的灰度秘密图像.相对于传统的视觉密码方案,本文方案在不影响视觉密码恢复图像的视觉质量前提下,可以隐藏更多的秘密图像信息,而像素扩张尺寸较小.     

基于多项式秘密共享的图像密文域可逆信息隐藏

针对密文域可逆信息隐藏在多用户场景下算法嵌入率低、载体图像容灾性能较弱等问题，该文提出一种基于多项式秘密共享的图像密文域可逆信息隐藏方案。通过将图像分割成多幅影子图像并存储在不同的用户端，可以增强图像的容灾性，为了实现额外信息在图像重构前后提取的可分离性，该方案包括两种嵌入算法:算法1在图像分割的过程中，将额外信息嵌入多项式的冗余系数中得到含有额外信息的影子图像，该算法支持在图像重构之后提取额外信息；算法2针对图像分割后的任一影子图像，利用秘密共享的加法同态特性实施嵌入，该算法支持直接从影子图像中提取额外信息。实验在不同门限方案和影子图像压缩率的条件下进行测试，当压缩率为50%时，(3, 4)门限方案的嵌入率达4.18 bpp(bit per pixel)，(3, 5)门限方案的嵌入率达3.78 bpp。结果表明，两种嵌入算法分别支持从影子图像与重构图像中提取额外信息，实现了方案的可分离性；与现有方案相比，所提算法嵌入率较高、计算复杂度较低，具有较强的实用性。     

(t,k, n) XOR-based visual cryptography scheme with essential shadows

Visual cryptography scheme (VCS) shares a binary secret image into multiple shadows, only qualified set of shadows can reveal the secret image by stacking operation. However, VCS suffers the problems of low visual quality of the revealed image and large shadow size. A (t, k, n) XOR-based visual cryptography scheme (XVCS) shares the secret image into n shadows including t essentials and n-t non-essentials. A qualified set of shadows contains any k shadows including t essentials. The revealing process is implemented by XOR operation on the involved shadows. In this paper, we propose a construction method for (t, k, n)-XVCS with essential shadows. The secret image can be revealed perfectly, and the shadow size is small compared with VCS. Theoretical analysis and experimental results show the security and effectiveness of the proposed scheme.     

多版本备份和限制性双重认证主密钥(t,s,k,n)图像分存

传统影子图像连接的（t,s,k,n）分存易导致分发影子图像大小不等,基于伯克霍夫插值的（t,s,k,n）分存不能高效恢复;而双认证自修复图像分存对密图和备份图恢复能力十分有限.针对以上问题,采用随机参与值通过（k,s）和（k-t,n-s）分存来构造主密钥（t,s,k,n）分存并通过第3方公信方存储的MD5值以防止作弊.所提策略由主密钥对密图LL子带置乱来形成对显著比特多备份、对非显著比特少备份和经主密钥不同程度置乱的多版本备份图;引入限制性双重认证在保持认证精度的同时,将尽可能多的备份比特通过GF（2^8）域（k,n）分存嵌入来形成嵌密掩体.理论和实验表明,主密钥（t,s,k,n）分存可高效求解;随机参与值可避免参与者编号泄露,分发信息的篡改和认证比特的揣测;多版本备份可对备份图高置信度地恢复;而限制性双重认证在认证能力上不低于双认证自修复图像分存.     

A blind watermarking algorithm based on fractional Fourier transform and visual cryptography

This paper presents a robust copyright protection scheme based on fractional Fourier transform (FrFT) and visual cryptography (VC). Unlike the traditional schemes, in our scheme, the original image is not modified by embedding the watermark into the original image. We use the visual secret sharing scheme to construct two shares, namely, master share and ownership share. Features of the original image are extracted using SVD, and are used to generate the master share. Ownership share is generated with the help of secret image (watermark) and the master share, using VC technique. The two shares separately give no information about the secret image, but for ownership identification, the secret image can be revealed by stacking the master share and the ownership share. In order to achieve the robustness and security, the properties of VC, FrFT and SVD are used in our scheme. The experimental results show that the proposed scheme is strong enough to resist various signal processing operations.     

User-friendly secret image sharing scheme with verification ability based on block truncation coding and error diffusion

Conventional secret image sharing schemes, which are constructed based on Shamir’s method, often suffer from random-liked shares, lossy reconstruction and high computation complexity. In addition, their generated shares are generally in original image format which may lead to more storage and suspicion from invaders. In this paper, we propose a user-friendly secret image sharing scheme based on block truncation coding (BTC) and error diffusion, where meaningful shares can be directly generated without any extra process. The meaningful shares by the proposed scheme are in BTC-compressed format which can reduce the capacity of transfer and storage. In the reconstructing phase, the secret image can be losslessly reconstructed by performing XOR operations on bit planes of sufficient BTC-compressed shares. Further, the proposed scheme provides extra verification ability to identify cheaters and check false shares. Theoretical analysis and simulation results demonstrate the feasibility of the proposed scheme.     

A Visual Secret Sharing Scheme for Progressively Restoring Secrets

Visual secret sharing has received more and more attention over the past years due to the fact that neither complex computation nor cryptographic knowledge is required to decrypt the secret image directly according to the characteristics of the human vision system. Considering the issue of sharing the secret image at multiple image resolutions with the meaningful shadows, in this paper, we present a friendly progressive visual secret sharing scheme without expanding the image size in the shadows and the reconstructed secret image based on applying a 22-sized block-wise operation to generate the shadows block by block. The proposed method can achieve these benefits: 1) the generated shadows are meaningful, and their sizes are not expanded, and 2) the secret image can be recovered at different resolutions by stacking different quantities of shadows together. The experimental results also show that the proposed method is superior to other compared schemes.     

双重门限秘密共享方案

基于RSA密码体制、Shamir门限方案和哈希函数的安全性,设计了一种双重门限秘密共享方案。方案中,参与者只需维护一个秘密份额,可实现对多个秘密的共享。秘密份额由参与者确定和保管,秘密分发者也不知晓,秘密共享过程中,只需出示伪秘密份额。方案不需要维护安全信道,算法能够保证信息安全传送,以及验证参与者是否进行了欺骗。     

一种可验证的基于超混沌系统的灰度图像多密钥共享算法

提出一种可验证的图像多密钥共享方案。算法中,灰度图像首先被置乱,而后划分为多个图像子块,利用图像子块的哈希值作为超混沌系统的初始值,生成多个随机网格(RG),最后利用RG和图像子块的异或生成共享的多个子密钥。提出的算法具有共享密钥空间小、能够无损恢复秘密图像,同时能够验证密钥的持有者是否对密钥进行了恶意篡改,能应用于重要领域如医学以及军事图像的保护。实验结果和对算法的比较分析,验证了算法的有效性。     

基于随机网格的视觉多秘密共享方案

为了提高视觉秘密共享(VSS)的恢复效果,该文提出一种基于随机网格的视觉多秘密共享方案.通过使用一种基于圆柱面的随机网格阈值多秘密图像共享方案,使得用户一次可以共享多个秘密图像;部分份额图像受到篡改仍然可以恢复秘密图像,具有较好的鲁棒性;同时份额的数量和最后恢复图像的视觉质量成正相关.仿真结果表明所提出的多秘密视觉共享...     

Efficient multi-secret image sharing based on Boolean operations

(n,n) visual secret sharing (VSS), first proposed by Naor and Shamir (1995) [4], is used to encode (encrypt) a secret image into n meaningless share images to be superimposed later to decode (decrypt) the original secret by human visual system after collecting all n secret images. In recent years, VSS-based image sharing (encryption) and image hiding schemes, two of a variety of applications based on VSS, have drawn much attention. In this paper, an efficient (n+1,n+1) multi-secret image sharing scheme based on Boolean-based VSS is proposed to not only keep the secret images confidential but also increase the capacity of sharing multiple secrets. The Boolean-based VSS technology, used to encode the secret images, generates n random matrices; then the n secret images are subsequently encoded into the n+1 meaningless share images. It is worthwhile to note that n secret images can be hidden by means of sharing only n+1 share images in the proposed scheme instead of 2n share images. Thus, the present scheme thus benefits from (1) reducing the demand of image transmission bandwidth, (2) easing the management overhead of meaningless share images, and (3) involving neither significant extra computational cost nor distortion for reconstructed secret images. The experimental results show the performance in terms of feasibility and image sharing capacity. Applied into image hiding schemes, the proposed scheme can enhance the hiding capacity.     

一个有效的门限多重秘密共享体制

针对Chien-Jan-Tseng体制计算量大以及Yang-Chang-Hwang体制公开信息量大的不足,利用双变量单向函数提出了一个新的(t,n)门限多重秘密共享体制.通过一次秘密共享过程就可以实现对任意个秘密的共享,而参与者秘密份额的长度仅为一个秘密的长度.在秘密重构过程中,每个合作的参与者只需提交一个由秘密份额计算的伪份额,而不会暴露其秘密份额本身.本文体制结合了现有体制的优点并避免了它们的缺点,是一个实用、有效的体制.     

AN EFFICIENT AND SECURE （t, n） THRESHOLD SECRET SHARING SCHEME

Based on Shamir＇s threshold secret sharing scheme and the discrete logarithm problem, a new （t, n） threshold secret sharing scheme is proposed in this paper. In this scheme, each participant＇s secret shadow is selected by the participant himself, and even the secret dealer cannot gain anything about his secret shadow. All the shadows are as short as the shared secret. Each participant can share many secrets with other participants by holding only one shadow. Without extra equations and information designed for verification, each participant is able to check whether another participant provides the true information or not in the recovery phase. Unlike most of the existing schemes, it is unnecessary to maintain a secure channel between each participant and the dealer. Therefore, this scheme is very attractive, especially under the circumstances that there is no secure channel between the dealer and each participant at all. The security of this scheme is based on that of Shamir＇s threshold scheme and the difficulty in solving the discrete logarithm problem. Analyses show that this scheme is a computationally secure and efficient scheme.     

Information hiding in the sharing domain

Secret image sharing (SIS) can divide a secret image into several shadow images for protection. Information hiding in the sharing domain (IHSD) fuses SIS and information hiding (IH) to simultaneously share any secret image and hide any information, and this technique can be applied in cloud computing, law enforcement and medical diagnoses. IHSD not only marks shadow images with information to prevent malicious tampering and for convenient management, search and identification but also enhances the robustness of IH. In this paper, we first introduce a formal definition of IHSD. Then, we describe a general IHSD model and algorithms with a concrete example in detail. In IHSD, we design the random element utilization model to control the random pixels generated from SIS. Then, we obtain shadow images with hidden information to realize SIS and IH simultaneously. The inputs of SIS with secret images, steganography and extra information in algorithms are without any limitations. Theoretical analyses, experiments and comparisons are presented to prove the effectiveness and feasibility of IHSD.