点击2010年中考中的密码问题

密码问题是近几年中考试卷中出现的一类新的命题类型.它涉及到密码学中密码编码和密码破译的知识,前者是对信息保密,后者     

通信密码简介(一)

<正>利用密码传送和储存信息是保证信息安全的一项最有效措施.在近代历史上,通信的保密措施,对军事和外交等方面有极端重要的意义,它直接关系到国家的安危和战争的胜负.例如,二战时期,美国密码专家用几个月时间完全破译了日本的密码"紫密".在中途岛一战,美国海军以劣     

通信密码简介(二)

<正>公钥密码体制是1976年由笛费(Diffie),海尔曼(Hellman)以及默克勒(Merkle)提出的新型密码体制,是对传统密码体制的重大突破.一、提出公钥密码体制的背景和基本思路传统密码体制的一个基本缺点是,在任何密文未发送之前,发方和收方之间必须利用安全通道,预先进行通信,将解密密钥通知对方.在实际应用中这是非常困难的.在战争年代,传送密码的人可能被敌方识破,密码也可能被敌方截获.     

保密通信的发展概况

我国将从 2 0 0 4年 9月开始实验普通高中数学课程标准 ,其中选修系列 3有专题 :信息安全与密码 .冯克勤教授的文章就是结合“新课标”而写 ,对教师和学生了解“信息安全与密码”很有帮助 ,也是为教师在讲授“信息安全与密码”前做思想和业务准备 .     

动态图形运动变化规律的定性和定量分析

定性分析主要是凭直觉、经验和被分析对象的信息资料,对研究对象的性质、特点和变化规律作出判断．定量分析是依据已知信息,通过计算和逻辑推理,分析对象的性质、特点和变化规律．定性分析与定量分析是相互补充的,定性分析常依据感知迅速地对问题作出判断,思维具有简约性,它是定量分析的前提,没有定性的定量是盲目的、毫无价值的．而定量分析使定性更科学、准确,它可以促使定性分析得出严谨和正确的结论．     

信息披露扭曲下企业债券违约风险量化研究

信息披露的真实性会直接影响到投资者对企业债券违约风险自々判断。利用信息噪声的偏倚性捕获财务报告信息中对资产价值的故意扭曲,推导了信息偏误下资产价值的条件分布、违约概率和信用价差的解析表达式.数值分析表明当资产价值遭到不同方向的扭曲时,信息噪声与违约概率会表现出不同的变动关系。实证检验表明该模型可以较为准确的刻画财务信息扭曲造成的债券违约风险和信用价差的变化规律。该模型为理解债券违约风险和财务报告信息扭曲之间的关系提供了新的启发,可以帮助债券投资者在信息披露问题比较严重的市场环境中评估违约风险。     

基于脉冲响应函数的降水和气温与径流变化的关系研究

依据渭河流域下游水文代表站和气象代表站1960～2005年的径流、降水和气温资料,采用脉冲响应函数和方差分解法,对降水和气温与径流变化的关系进行研究.结果表明,降水对径流变化具有正向促进作用,径流对降水变化具有弱促进作用;气温对径流变化具有反向促进作用,径流对气温变化具有弱反向促进作用.径流的预测误差,主要来自于降水所做的贡献,其次是自身冲击和气温的扰动对其的贡献.     

《上海中学数学》投稿指南

为了向广大作者提供更为便捷的投稿方式,经研究决定,从2018年6月1日起,《上海中学数学》杂志提供两种投稿方式。第一种方式为网上投稿系统投稿。您可以登陆我刊官网(http://shzxsx.shnu.edu.cn),进入投稿系统投稿。请您根据系统提示完成新用户注册,以注册的用户名及密码登录,点击"插入全文"上传稿件,点击"下一步"填写稿件及作者信息,完成投稿。     

多元地学信息挖掘中分层动量增项自适应BP算法应用研究

地球化学元素分布规律的研究是揭示元素矿化富集及空间变化规律的重要途径之一,采用人工神经网络方法对东天山地区地球化学信息进行了研究,为矿区靶区预测提供支持.对传统BP算法进行了改进,采用分层动量增项自适应BP算法设计,并完成了样本区数据的预测分析,效果较好.     

RAINBOW分组密码的线性密码分析

本文在对RAINBOW分组密码的基础模块深入研究和测试后,利用扩散层的特点,对RAINBOW分组密码进行了线性密码分析,攻击的数据复杂度为294,计算复杂度小于218.此结果显示RAINBOW分组密码对线性密码分析是不免疫的.     

A Partition of the Hypercube into Maximally Nonparallel Hamming Codes

By using the Gold map, we construct a partition of the hypercube into cosets of Hamming codes such that for every two cosets the corresponding Hamming codes are maximally nonparallel, that is, their intersection cardinality is as small as possible to admit nonintersecting cosets.     

环F_2+uF_2+u~2F_2上线性码的MacWilliams恒等式

记R=F_2+uF_2+u~2F_2,定义了环R上码字的李重量分布的概念,构造了从R~n到F_2~(3n)的Gray映射φ.通过对环R上线性码及其对偶码生成矩阵的研究,证明了环R上线性码及其对偶码的Gray象是F_2上的对偶码.利用域F_2上线性码及其对偶码的重量分布关系,得到了环R上线性码及其对偶码关于李重量分布的MacWilliams恒等式.     

Quasi-cyclic codes as cyclic codes over a family of local rings

We give an algebraic structure for a large family of binary quasi-cyclic codes. We construct a family of commutative rings and a canonical Gray map such that cyclic codes over this family of rings produce quasi-cyclic codes of arbitrary index in the Hamming space via the Gray map. We use the Gray map to produce optimal linear codes that are quasi-cyclic.     

Cyclic codes over <Emphasis Type="Italic">R</Emphasis><Subscript><Emphasis Type="Italic">k</Emphasis></Subscript>

Cyclic codes over an infinite family of rings are defined. The general properties of cyclic codes over these rings are studied, in particular nontrivial one-generator cyclic codes are characterized. It is also proved that the binary images of cyclic codes over these rings under the natural Gray map are binary quasi-cyclic codes of index 2 ^k . Further, several optimal or near optimal binary codes are obtained from cyclic codes over R _k via this map.     

On Upper Bounds for Minimum Distance and Covering Radius of Non-binary Codes

We consider upper bounds on two fundamental parameters of a code; minimum distance and covering radius. New upper bounds on the covering radius of non-binary linear codes are derived by generalizing a method due to S. Litsyn and A. Tietäväinen lt:newu and combining it with a new upper bound on the asymptotic information rate of non-binary codes. The upper bound on the information rate is an application of a shortening method of a code and is an analogue of the Shannon-Gallager-Berlekamp straight line bound on error probability. These results improve on the best presently known asymptotic upper bounds on minimum distance and covering radius of non-binary codes in certain intervals.     

Linear codes from vectorial Boolean power functions

In this paper, three classes of binary linear codes with few weights are proposed from vectorial Boolean power functions, and their weight distributions are completely determined by solving certain equations over finite fields. In particular, a class of simplex codes and a class of first-order Reed-Muller codes can be obtained from our construction by taking the identity map, whose dual codes are Hamming codes and extended Hamming codes, respectively.     

环F2＋uF2上偶长的（1＋u）-常循环码

给出了环F2＋uF2上任意偶长的（1＋u）-常循环码的结构，确定了给定偶长度F2＋uF2上（1＋u）-常循环码的数目．通过Gray映射，得到了F2＋uF2上偶长的（1＋u）-常循环码的二元象．     

环F_2+uF_2上偶长的(1+u)-常循环码

给出了环F2+uF2上任意偶长的(1+u)-常循环码的结构,确定了给定偶长度F2+uF2上(1+u)-常循环码的数目.通过Gray映射,得到了F2+uF2上偶长的(1+u)-常循环码的二元象.     

环F_2+uF_2上线性码的二元像

在有限环R=F2+uF2与F2之间定义了一个新的Gray映射,给出了环F2+uF2上线性码C的二元像φ(C)的生成矩阵,证明了环F2+uF2上线性码C及其对偶码的二元像仍是对偶码.     

2n Bordered constructions of self-dual codes from group rings

Self-dual codes, which are codes that are equal to their orthogonal, are a widely studied family of codes. Various techniques involving circulant matrices and matrices from group rings have been used to construct such codes. Moreover, families of rings have been used, together with a Gray map, to construct binary self-dual codes. In this paper, we introduce a new bordered construction over group rings for self-dual codes by combining many of the previously used techniques. The purpose of this is to construct self-dual codes that were missed using classical construction techniques by constructing self-dual codes with different automorphism groups. We apply the technique to codes over finite commutative Frobenius rings of characteristic 2 and several group rings and use these to construct interesting binary self-dual codes. In particular, we construct some extremal self-dual codes of length 64 and 68, constructing 30 new extremal self-dual codes of length 68.