密码编码学与网络安全(第五版)答案.doc
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1、Chapter 1:Introduction5Chapter 2:Classical Encryption Techniques7Chapter 3:Block Ciphers and the Date Encryption Standard13Chapter 4:Finite Fields21Chapter 5:Advanced Encryption Standard28Chapter 6:More on Symmetric Ciphers33Chapter 7:Confidentiality Using Symmetric Encryption38Chapter 8:Introductio
2、n to Number Theory42Chapter 9:PublicKey Cryptography and RSA46Chapter 10:Key Management; Other PublicKey Cryptosystems55Chapter 11:Message Authentication and Hash Functions59Chapter 12:Hash and MAC Algorithms62Chapter 13:Digital Signatures and Authentication Protocols66Chapter 14:Authentication Appl
3、ications71Chapter 15:Electronic Mail Security73Chapter 16:IP Security76Chapter 17:Web Security80Chapter 18:Intruders83Chapter 19:Malicious Software87Chapter 20:Firewalls89Answers to Questions1.1The OSI Security Architecture is a framework that provides a systematic way of defining the requirements f
4、or security and characterizing the approaches to satisfying those requirements. The document defines security attacks, mechanisms, and services, and the relationships among these categories.1。2Passive attacks have to do with eavesdropping on, or monitoring, transmissions。 Electronic mail, file trans
5、fers, and client/server exchanges are examples of transmissions that can be monitored。 Active attacks include the modification of transmitted data and attempts to gain unauthorized access to computer systems。1.3Passive attacks: release of message contents and traffic analysis。 Active attacks: masque
6、rade, replay, modification of messages, and denial of service.1。4Authentication: The assurance that the communicating entity is the one that it claims to be. Access control: The prevention of unauthorized use of a resource (i.e., this service controls who can have access to a resource, under what co
7、nditions access can occur, and what those accessing the resource are allowed to do)。 Data confidentiality: The protection of data from unauthorized disclosure。 Data integrity: The assurance that data received are exactly as sent by an authorized entity (i.e。, contain no modification, insertion, dele
8、tion, or replay)。 Nonrepudiation: Provides protection against denial by one of the entities involved in a communication of having participated in all or part of the communication。 Availability service: The property of a system or a system resource being accessible and usable upon demand by an author
9、ized system entity, according to performance specifications for the system (i.e。, a system is available if it provides services according to the system design whenever users request them). 1.5See Table 1。3。Answers toProblems1.1Release of message contentsTraffic analysisMasqueradeReplayModification o
10、f messagesDenial of servicePeer entity authenticationYData origin authenticationYAccess controlYConfidentialityYTraffic flow confidentialityYData integrityYYNon-repudiationYAvailabilityY1。2Release of message contentsTraffic analysisMasqueradeReplayModification of messagesDenial of serviceEnciphermen
11、tYDigital signatureYYYAccess controlYYYYYData integrityYYAuthentication exchangeYYYYTraffic paddingYRouting controlYYYNotarizationYYYChapter 2Classical Encryption TechniquesrAnswers to Questions2.1Plaintext, encryption algorithm, secret key, ciphertext, decryption algorithm.2。2Permutation and substi
12、tution。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 a block of plaintext is treated as a whole and used to produce a ciphertext block of equal length。2。5Cr
13、yptanalysis and brute force。2。6Ciphertext only. One possible attack under these circumstances is the bruteforce approach of trying all possible keys. If the key space is very large, this becomes impractical。 Thus, the opponent must rely on an analysis of the ciphertext itself, generally applying var
14、ious 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 deduce the key on the basis of the way in which the known plaintext is transformed. Chosen plaintext。 If the
15、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 secure if the ciphertext generated by the scheme does not contain enough information to determine uniquely
16、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 the encrypted information, and (2) the time required to break the cipher exceeds the useful lifetime of the
17、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 monoalphabetic substitution cipher maps a plaintext alphabet to a ciphertext alphabet, so that each letter of the plaintex
18、t alphabet maps to a single unique letter of the ciphertext alphabet.2。10The Playfair algorithm is based on the use of a 5 5 matrix of letters constructed using a keyword. Plaintext is encrypted two letters at a time using this matrix。2.11A polyalphabetic substitution cipher uses a separate monoalph
19、abetic substitution cipher for each successive letter of plaintext, depending on a key.2。121。 There is the practical problem of making large quantities of random keys. Any heavily used system might require millions of random characters on a regular basis. Supplying truly random characters in this vo
20、lume is a significant task。2. Even more daunting is the problem of key distribution and protection. For every message to be sent, a key of equal length is needed by both sender and receiver。 Thus, a mammoth key distribution problem exists.2。13A transposition cipher involves a permutation of the plai
21、ntext letters。2。14Steganography involves concealing the existence of a message。Answers to Problems2.1a.No. A change in the value of b shifts the relationship between plaintext letters and ciphertext letters to the left or right uniformly, so that if the mapping is one-to-one it remains oneto-one。b。2
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- 密码 编码 网络安全 第五 答案
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