컴퓨터 통신보안(그린사) 연습문제 풀이

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연습문제 풀이 입니다.

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Chapter 2: Classical Encryption Techniques
Chapter 3: Block Ciphers and the Date Encryption Standard
Chapter 4: Introduction to Finite Fields
Chapter 5: Advanced Encryption Standard
Chapter 6: Contemporary Symmetric Ciphers
Chapter 7: Confidentiality Using Symmetric Encryption
Chapter 8: Introduction to Number Theory
Chapter 9: Public-Key Cryptography and RSA
Chapter 10: Key Management; Other Public-Key Cryptosystems
Chapter 11: Message Authentication and Hash Functions
Chapter 12: Hash and MAC Algorithms
Chapter 13: Digital Signatures and Authentication Protocols
Chapter 14: Authentication Applications
Chapter 15: Electronic Mail Security
Chapter 16: IP Security
Chapter 17: Web Security
Chapter 18: Intruders
Chapter 19: Malicious Software
Chapter 20: Firewalls

본문내용

CHAPTER 2
CLASSICAL ENCRYPTION TECHNIQUES

ANSWERS TO QUESTIONS

2.1 Plaintext, encryption algorithm, secret key, ciphertext, decryption algorithm.
2.2 Permutation and substitution.
2.3 One key for symmetric ciphers, two keys for asymmetric ciphers.
2.4 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 plaintext is treated as a whole and
used to produce a ciphertext block of equal length.
2.5 Cryptanalysis and brute force.
2.6 Ciphertext 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 becomes
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 deduce the key on the basis of the
way in which the known plaintext is transformed.

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