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1、本资源来自数缘社区 :81 欢迎来到数缘社区。本社区是一个高等数学及密码学的技术性论坛，由山东大学数学院研究 生创办。在这里您可以尽情的遨游数学的海洋。作为站长，我诚挚的邀请您加入，希望大家能一 起支持发展我们的论坛，充实每个版块。把您宝贵的资料与大家一起分享！ 数学电子书库 每天都有来源于各类网站的与数学相关的新内容供大家浏览和下载， 您既可以点击左键弹出 网页在线阅读，又可以点右键选择下载。现在书库中藏书 1000 余本。如果本站没有您急需的电 子书，可以发帖说明，我们有专人负责为您寻找您需要的电子书。 密码学论文库 国内首创信息安全专业的密码学论文库，主要收集欧密会（Eurocrypt）
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4、见。 附录 A：本站电子书库藏书目录 :81/bbs/dispbbs.asp?boardID=18 Other Public-Key Cryptosystems.42 Chapter 11:Message Authentication and Hash Functions.45 Chapter 12:Hash and MAC Algorithms48 Chapter 13:Digital Signatures and Authentication Protocols50 Chapter 14:Authentication Applications54 Chapter 15:Electronic
5、 Mail Security57 Chapter 16:IP Security.60 Chapter 17:Web Security.65 Chapter 18:Intruders68 Chapter 19:Malicious Software.72 Chapter 20:Firewalls74 -3- NOTICE This manual contains solutions to all of the review questions and homework problems in Cryptography and Network Security, Third Edition. If
6、you spot an error in a solution or in the wording of a problem, I would greatly appreciate it if you would forward the information via email to me at ws . An errata sheet for this manual, if needed, is available at ftp:/ W.S. -4- A A A NSWERS TO NSWERS TO NSWERS TO QQ QUESTIONSUESTIONSUESTIONS 2.1Pl
7、aintext, encryption algorithm, secret key, ciphertext, decryption algorithm. 2.2Permutation and substitution. 2.3One key for symmetric ciphers, two keys for asymmetric ciphers. 2.4A stream cipher is one that encrypts a digital data stream one bit or one byte at a time. A block cipher is one in which
8、 a block of plaintext is treated as a whole and used to produce a ciphertext block of equal length. 2.5Cryptanalysis and brute force. 2.6Ciphertext only. One possible attack under these circumstances is the brute-force approach of trying all possible keys. If the key space is very large, this become
9、s impractical. Thus, the opponent must rely on an analysis of the ciphertext itself, generally applying various statistical tests to it. Known plaintext. The analyst may be able to capture one or more plaintext messages as well as their encryptions. With this knowledge, the analyst may be able to de
10、duce the key on the basis of the way in which the known plaintext is transformed. Chosen plaintext. If the analyst is able to choose the messages to encrypt, the analyst may deliberately pick patterns that can be expected to reveal the structure of the key. 2.7An encryption scheme is unconditionally
11、 secure if the ciphertext generated by the scheme does not contain enough information to determine uniquely the corresponding plaintext, no matter how much ciphertext is available. An encryption scheme is said to be computationally secure if: (1) the cost of breaking the cipher exceeds the value of
12、the encrypted information, and (2) the time required to break the cipher exceeds the useful lifetime of the information. 2.8The Caesar cipher involves replacing each letter of the alphabet with the letter standing k places further down the alphabet, for k in the range 1 through 25. 2.9A monoalphabet
13、ic substitution cipher maps a plaintext alphabet to a ciphertext alphabet, so that each letter of the plaintext alphabet maps to a single unique letter of the ciphertext alphabet. 2.10 The Playfair algorithm is based on the use of a 5 5 matrix of letters constructed using a keyword. Plaintext is enc
14、rypted two letters at a time using this matrix. 2.11 A polyalphabetic substitution cipher uses a separate monoalphabetic substitution cipher for each successive letter of plaintext, depending on a key. CHAPTER 2 CLASSICAL ENCRYPTION TECHNIQUES -5- 2.12 1. There is the practical problem of making lar
15、ge quantities of random keys. Any heavily-used system might require millions of random characters on a regular basis. Supplying truly random characters in this volume is a significant task. 2. Even more daunting is the problem of key distribution and protection. For every message to be sent, a key o
16、f equal length is needed by both sender and receiver. Thus, a mammoth key distribution problem exists. 2.13 A transposition cipher involves a permutation of the plaintext letters. 2.14 Steganography involves concealing the existence of a message. A A A NSWERS TO NSWERS TO NSWERS TO P P P ROBLEMSROBLEMSROBLEMS 2.1 A good glass in the Bishops hostel in the Devils seattwenty-one degrees and thirteen minutesnortheast and by northmain branch seventh limb east sideshoot from the left ey
