Threshold Visual Cryptography Schemes with Specified Whiteness Levels of Reconstructed Pixels

In 1994, Naor and Shamir introduced an unconditionally secure method for encoding black and white images. This method, known as a threshold visual cryptography scheme (VCS), has the benefit of requiring no cryptographic computation on the part of the decoders. In a -VCS, a share, in the form of a transparency, is given to ">n users. Any ">k users can recover the secret simply by stacking transparencies, but ">k-1 users can gain no information about the secret whatsoever.In this paper, we first explore the issue of contrast, by demonstrating that the current definitions are inadequate, and by providing an alternative definition. This new definition motivates an examination of minimizing pixel expansion subject to fixing the VCS parameters ">h and ">l. New bounds on pixel expansion are introduced, and connections between these bounds are examined. The best bound presented is tighter than any previous bound. An analysis of connections between (2, ">n) schemes and designs such as BIBD's, PBD's, and (">r, )-designs is performed. Also, an integer linear program is provided whose solution exactly determines the minimum pixel expansion of a (2, ">n)-VCS with specified ">h and >l.     

Arithmetic on superelliptic curves

This paper is concerned with algorithms for computing in the divisor class group of a nonsingular plane curve of the form which has only one point at infinity. Divisors are represented as ideals, and an ideal reduction algorithm based on lattice reduction is given. We obtain a unique representative for each divisor class and the algorithms for addition and reduction of divisors run in polynomial time. An algorithm is also given for solving the discrete logarithm problem when the curve is defined over a finite field.

     

基于身份的带凭证部分委托代理多重签名方案

本文基于椭圆曲线上的双线性对性质，提出了一个基于身份的带凭证部分委托代理多重签名方案，该方案具有强不可伪造性、强不可否认性、强可识别性和预防误用性．     

一种基于指纹的身份认证协议

提出一种基于指纹的身份认证协议,它对stolen-verifier(攻击者使用从认证服务器中盗窃的用户指纹信息冒充合法用户)和重发攻击 (Replay Attack)[1]是安全的,保证了用户指纹信息的保密性和真实性。认证用户可以从中获得的最大好处就是:当他们登录服务系统时,他们不需要除了指纹以外的其它任何东西。1     

有限秘密下指派秘密共享方案的构造

针对有限个秘密要分享的情况，提出了一种具有指派功能秘密共享方案的新实现方法。为了说明这一方法，给出了两个实现方案：第一个方案通过引入碎片向量的概念来实现；第二个方案通过引入秘密偏移量的概念来对第一个方案进行优化，能够达到对分享着资源的充分利用。和以往的方案相比．这些方案要求更低的通讯和计算成本；且更加合理和容易实施。     

加密小区广播中的密钥管理

论文提出了一种改进的安全锁方案,并将改进后的安全锁应用于加密小区广播的密钥管理,增加了加密小区广播中密钥管理的安全强度,保证了前向安全和后向安全,能够有效降低密钥管理的计算开销和网络通信开销。     

椭圆曲线密码处理器的高效VLSI设计与实现

采用复合武硬件设计方法，通过数学公式推导和电路结构设计，完成了一款GF（2m）域椭圆曲线密码处理器的高效VLSI实现。以低成本为目标，对算术逻辑模块的乘法、约减、平方、求逆，以及控制电路模块都进行了优化设计。按照椭圆曲线密码的不同运算层次，设计了不同层次的控制电路。该处理器综合在中芯国际SMIC0．18μm标准工艺库上．比相关研究的芯片面积节省48％，同时保证了很快的速度。     

Madsen求阶算法的改进和推广

文章分析了仅适用于特征为2和3的域上的一种椭圆曲线求阶算法—Madsen求阶算法,并对此算法进行了改进和推广,提高了Madsen算法的运算速度。     

On the Contrast in Visual Cryptography Schemes

A visual cryptography scheme is a method to encode a secret image SI into shadow images called shares such that certain qualified subsets of shares enable the ``visual' recovery of the secret image. The ``visual' recovery consists of xeroxing the shares onto transparencies, and then stacking them. The shares of a qualified set will reveal the secret image without any cryptographic computation. In this paper we analyze the contrast of the reconstructed image in k out of n visual cryptography schemes. (In such a scheme any k shares will reveal the image, but no set of k-1 shares gives any information about the image.) In the case of 2 out of n threshold schemes we give a complete characterization of schemes having optimal contrast and minimum pixel expansion in terms of certain balanced incomplete block designs. In the case of k out of n threshold schemes with we obtain upper and lower bounds on the optimal contrast. Received 27 September 1996 and revised 13 February 1998