第3章分组密码习题 1.证明DES的解密变换是加密变换的逆 2.对DES进行穷搜索攻击时,需要在由2-个密钥空间进行。能否根据明文、密钥、密文之间的互补关系(即:若C=DESk(P)则C=DESe(P))减小进行穷搜索攻击时所用的密钥空间?试说明原因

第1章概论习题 1.就你所在单位的某个信息系统,试做一个概略的安全风险评估? 2.网络上查找出分组秘密码DES(基本型)原程序或资料,回答:DES的密钥空间大小?

包括以下21门课程：运筹学、信息安全数学基础、复变函数、数学建模、工具软件、信息工程概论、微分方程数值解、图形图像处理、数学实验、信息与博弈、分析选讲、代数选讲、密码学、随机过程、软件工程、计算机网络、泛函分析、计算机图形学、信息论基础、网站规划与网页设计、统计与预测

Iterating Block ciphers Definition A product cipher combines two or more transformations in a manner intending that the resulting cipher is more secure than the individual components. Definition An iterated block cipher is a block cipher involving the sequential repetition of an internal function called a round function. Parameters include the number of rounds Nr, the block bitsize n, and the bitsize k of the input key K from which Nr subkeys Ki (round keys) are derived. For invertibility (allowing unique decryption), for each value Ki the round function is a bijection on the round input

Modular arithmetic – Used to define a finite field – a = b mod n means that if a and b are divided by n they produce the same remainder – a*b mod n can result in 0 even if a and b are not 0

Definitions – Digital Signature - a data string which associates a message with some originating entity – Digital Signature Generation Algorithm – a method for producing a digital signature – Digital signature verification algorithm - a method for verifying that a digital signature is authentic (i.e., was indeed created by the specified entity)

Definition: Group A set G of elements and operator @ form a group if: for all x,y in G, x @ y is also in G (inclusion) there is an identity element e such that for all x in G, e@x = x for all x in G, there is an inverse element x

A. J. Menezes, P. C. van Oorschot and S. A. Vanstone. Handbook of Applied Cryptography, CRC Press, 1997. Bruce Schneier. Applied Cryptography, Second Edition: Protocols, Algorthms, and Source Code in C (cloth) John Wiley & Sons, Inc.) 1996 Douglas R. Stinson, Cryptography (Theory and Practice), CRC Press 1995 Resources

Security Attack: Any action that compromises the security of information. Security Mechanism: A mechanism that is designed to detect, prevent, or recover from a security attack. Security Service: A service that enhances the security of data processing systems and information transfers. A security service makes use of one or more security mechanisms

Additional key-sizes and block-sizes Ability to function efficiently and securely in a wide variety of platforms and applications low-end smartcards, wireless: small memory requirements IPSec, ATM – small key setup time in hardware B-ISDN, satellite communication – large encryption speed Flexibility