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"网络平安技术"英文习题集
Chapter 1 Introduction
ANSWERS NSWERS TO QUESTIONS
What to performance specifications for the system (., a system is available if it provides services according to the system design whenever users request them).
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Chapter2 Symmetric Encryptionand Message Confidentiality
ANSWERS NSWERS TO QUESTIONS
What are the essential ingredients of a symmetric cipher"
Plainte*t, encryption algorithm, secret key, cipherte*t, decryption algorithm.
What are the two basic functions used in encryption algorithms"
Permutation and substitution.
How many keys are required for two people to municate via a symmetric cipher"
One secret key.
What is the difference between a block cipher and a stream cipher"
A 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 plainte*t is treated as a whole and used to produce a cipherte*t block of equal length.
What are the two general approaches to attacking a cipher"
Cryptanalysis and brute force.
Why do some block cipher modes of operation only use encryption while others use both encryption and decryption"
In some modes, the plainte*t does not pass through the encryption function, but is *ORed with the output of the encryption function. The math works out that for decryption in these cases, the encryption function must also be used.
What is triple encryption"
With triple encryption, a plainte*t block is encrypted by passing it through an encryption algorithm; the result is then passed through the same encryption algorithm again; the result of the second encryption is passed through the same encryption algorithm a third time. Typically, the second stage uses the decryption algorithm rather than the encryption algorithm.
Why is the middle portion of 3DES a decryption rather than an encryption"
There is no cryptographic s