Fast high-quality volume ray-casting with virtual samplings

Volume ray-casting with a higher order reconstruction filter and/or a higher sampling rate has been adopted in direct volume rendering frameworks to provide a smooth reconstruction of the volume scalar and/or to reduce artifacts when the combined frequency of the volume and transfer function is high. While it enables high-quality volume rendering, it cannot support interactive rendering due to its high computational cost. In this paper, we propose a fast high-quality volume ray-casting algorithm which effectively increases the sampling rate. While a ray traverses the volume, intensity values are uniformly reconstructed using a high-order convolution filter. Additional samplings, referred to as virtual samplings, are carried out within a ray segment from a cubic spline curve interpolating those uniformly reconstructed intensities. These virtual samplings are performed by evaluating the polynomial function of the cubic spline curve via simple arithmetic operations. The min max blocks are refined accordingly for accurate empty space skipping in the proposed method. Experimental results demonstrate that the proposed algorithm, also exploiting fast cubic texture filtering supported by programmable GPUs, offers renderings as good as a conventional ray-casting algorithm using high-order reconstruction filtering at the same sampling rate, while delivering 2.5x to 3.3x rendering speed-up.     

Extinction-based shading and illumination in GPU volume ray-casting

Direct volume rendering has become a popular method for visualizing volumetric datasets. Even though computers are continually getting faster, it remains a challenge to incorporate sophisticated illumination models into direct volume rendering while maintaining interactive frame rates. In this paper, we present a novel approach for advanced illumination in direct volume rendering based on GPU ray-casting. Our approach features directional soft shadows taking scattering into account, ambient occlusion and color bleeding effects while achieving very competitive frame rates. In particular, multiple dynamic lights and interactive transfer function changes are fully supported. Commonly, direct volume rendering is based on a very simplified discrete version of the original volume rendering integral, including the development of the original exponential extinction into a-blending. In contrast to a-blending forming a product when sampling along a ray, the original exponential extinction coefficient is an integral and its discretization a Riemann sum. The fact that it is a sum can cleverly be exploited to implement volume lighting effects, i.e. soft directional shadows, ambient occlusion and color bleeding. We will show how this can be achieved and how it can be implemented on the GPU.     

Secret sharing approaches for 3D object encryption

In this paper, we propose two secret sharing approaches for 3D models using Blakely and Thien and Lin schemes. We show that encoding 3D models using lossless data compression algorithms prior to secret sharing helps reduce share sizes and remove redundancies and patterns that possibly ease cryptanalysis. The proposed approaches provide a higher tolerance against data corruption/loss than existing 3D protection mechanisms, such as encryption. Experimental results are provided to demonstrate the secrecy and safety of the proposed schemes. The feasibility of the proposed algorithms is demonstrated on various 3D models.     

拉丁方秘密共享方案

针对拉丁方秘密共享方案存在的"初始化和重构困难、秘密共享过程中秘密分片的直接暴露可能会泄露整个秘密"等问题,提出一种拉丁方秘密共享方案.利用拉丁方"轮廓与合适的自合痕"可唯一恢复该拉丁方的特性,将随机生成的拉丁方作为"秘密",从该秘密拉丁方中随机选择"轮廓",经过合痕转换后进行秘密共享.分析结果表明该方案能够克服潜在的...     

针对类球形对象的改进光线投射算法

为提高光线投射算法的绘制速度和图像绘制质量,提出了一种针对类球形对象的改进光线投射算法。该算法首先设置球形包围盒的方法剔除对最后绘图结果没有影响的光线投射,用快速求交的方法来提高获取采样点的速度,通过自适应采样的方法加入新的采样点来提高绘制图像的质量。实验结果表明该算法不仅比传统方法绘制出的图像质量清晰,并且提高了算法的执行速度。     

Security-enhanced cloud-based image secret sharing and authentication using POB number system

Recently, the image secret sharing technique based on POB (Permutation Ordered Binary) number systems has drawn attention in academia. Thanks to Singh et al.’s pioneer in combining image confidentiality and authentication to form a cloud-based image cryptosystem using the POB number system. However, for image confidentiality and integrity, there are always two main concerns of a new image cryptosystem: the protection from unauthorized disclosure and the sensitivity of tampering. To claim confidentiality and integrity guaranty of secure image cryptosystems is meaningful only when the cryptanalysis is taken into consideration. In this article, Singh et al.’s scheme has undergone the scrutiny and potential security weaknesses found. First, the secret image may leak under chosen-plain-image attacks. Second, the partial secret key deducible under cipher/share-image-only attacks is shown unneglectable. Precisely, it is potentially problematic since the security of image authentication only relies on the secrecy of the parameter r of POB number systems, but the parameter is also learned to know by a heuristic method. The main weak design has been shown by means of introducing theoretical analyses and conducting some counter experiments. As a result, in this study we have focused on proposing a security-enhanced POB-based image secret sharing scheme with five primary advantages: (1) high security to confidentiality, (2) lossless reconstructed secret image, (3) high security to integrity, (4) high detection accuracy, and (5) low time complexity. The experimental results and the further analysis demonstrate that the simple and secure improvement does work.

     

用人工神经网络实现秘密共享

以人工神经网络为基础实现了一种秘密共享方案.该方案不同于已有的一些秘密共享方案,它利用人工神经网络分类、识别的性质,将参与恢复秘密的用户组合类比为人工神经网络的输入序列,通过训练,人工神经网络可以识别正确的用户组合并得到原始秘密.该秘密共享方案可以实现不同权限的用户所参与的秘密共享方案,但是不会增加存储或计算上的开销.     

Secret sharing based on quantum Fourier transform

Secret sharing plays a fundamental role in both secure multi-party computation and modern cryptography. We present a new quantum secret sharing scheme based on quantum Fourier transform. This scheme enjoys the property that each share of a secret is disguised with true randomness, rather than classical pseudorandomness. Moreover, under the only assumption that a top priority for all participants (secret sharers and recovers) is to obtain the right result, our scheme is able to achieve provable security against a computationally unbounded attacker.     

Secret sharing schemes from binary linear codes

In principle, every linear code can be used to construct a secret sharing scheme. However, in general, determining the access structure of the scheme is very hard. On the other hand, finding error correcting codes that produce secret sharing schemes with efficient access structures is also difficult. In this paper, we study a set of minimal codewords for certain classes of binary linear codes, and then determine the access structure of secret sharing schemes based on these codes. Furthermore, we prove that the secret sharing schemes obtained are democratic in the sense that every participant is involved in the same number of minimal access sets.     

无可信中心秘密共享加密模式

在基于椭圆曲线离散对数的安全机制的前提下,讨论了(t,n)门限加密模式.在该模式中,系统公钥由成员协同产生,t个或t个以上成员可以间接地解开密文.由于(t,n)门限加密模式秘密信息较少,所以具有良好的安全性,且计算复杂度较低.     

Secret image sharing with smaller shadow sizes for general access structures

In the area of secret image sharing (SIS), most papers focused on the schemes for threshold or some special access structures. Regarding general access structures (GAS), few results have been found in the literature. Two SIS schemes for GAS were proposed in 2001 and 2010, both are based on qualified sets. However, one distorts the reconstructed secret image, and some extra information is needed in both schemes. Here, we propose three polynomial based SIS schemes for GAS. Considering either qualified or forbidden sets, these schemes can reconstruct the secret image perfectly without any extra information needed. Some proof and analysis on the shadow sizes of the three schemes are given to lead us to choose the one with the smallest size. In addition, we also give some comparisons with two existing schemes, and security issue is also addressed in conclusion.     

Fast projection-based ray-casting algorithm for renderingcurvilinear volumes

We present an efficient and robust ray-casting algorithm for directly rendering a curvilinear volume of arbitrarily-shaped cells. By projecting cell-faces onto the image plane, we have effectively addressed three critical steps of the ray-casting process, namely finding the entry cell-faces for a ray, traversing along the ray from one cell to another, and reconstructing data values at the ray/cell-face intersections. Our algorithm significantly reduces rendering time, alleviates memory space consumption, and overcomes the conventional limitation requiring cells to be convex. Application of this algorithm to several commonly used curvilinear data sets has produced a favorable performance when compared with recently reported algorithms     

基于多用户双锁加密系统的密钥分存方案

对灰色加密理论中的多用户双锁加密系统进行了改进,提出了一种基于多用户双锁加密系统的密钥分存方案.该方案通过改变灰色微分方程x(0)(k) az(1)(k)=b中z(1)(k)的生成系数(权数),解决了密钥分存中密钥的更新和复用问题,并通过引入一简单的离散对数函数来抵御成员欺骗.     

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.     

基于猫映射和布尔运算的图像分存共享方法

为了提高图像可视分存共享的安全性,提出了一种基于改进 Arnold 变换和布尔运算的图像信息安全保护算法。该方法利用改进的非拟仿射 Arnold 变换对像素位置置乱,并利用该变换将其分解为两幅图像,将分解所得图像分别采用基于布尔运算的 r 轮(2,n)秘密共享方案实现可视分存。最后,对可视分存图像进行重构,并采用逆非拟仿射 Arnold 变换实现图像合成和置乱反变换恢复原图像,对其存在随机噪声采用改进中值滤波去噪。理论分析和实验结果均表明,所建议的组合式图像信息安全保护方法是有效的。     

Secret sharing: using meaningful image shadows based on Gray code

Steganography, such as secret sharing, is an important technique to use for protecting transmitted confidential data from the attention of any adversaries. Gray code is a commonly encountered binary labeling that was proposed by Frank Gray of Bell Laboratories in 1940 to prevent errors when using pulse-code modulation to transmit signals. The main features of Gray code are its recursive construction method and the fact that any two adjacent codes change only one bit. According to our observations, the image pixel correction based on these features is suitable for application secret sharing without making significant changes to the pixel value. We designed a reversible secret sharing method using meaningful image shadows based on Gray code. Our design applies absolute moment block truncation coding (AMBTC) compression to reduce the transmission bit rate. The experimental results show that our scheme can achieve the adequate visual quality of shadow images with lower communication overhead, thus proving it practical for numerous applications.     

CBC: Caching for cloud-based VOD systems

Cloud-based video on demand (VOD) service is a promising next-generation media streaming service paradigm. Being a resource-intensive application, how to maximize resource utilization is a key issue of designing such an application. Due to the special cloud-based VOD system architecture consisting of cloud storage cluster and media server cluster, existing techniques such as traditional caching strategies are inappropriate to be adopted by a cloud-based VOD system directly in practice. Therefore, in this study, we have proposed a systemic caching scheme, which seamlessly integrates a caching algorithm and a cache deployment algorithm together to maximize the resources utilization of cloud-based VOD system. Firstly, we have proposed a cloud-based caching algorithm. The algorithm models the cloud-based VOD system as a multi-constraint optimization problem, so as to balance the resource utilization between cloud storage cluster and media server cluster. Secondly, we have proposed a cache deployment algorithm. The algorithm further manages the bandwidth and cache space resource utilization inside the media server cluster in a more fine-grained manner, and achieves load balancing performance. Our evaluation results show that the proposed scheme enhances the resource utilization of the cloud-based VOD system under resource-constrained situation, and cuts down the reject ratio of user requests.