정보 보호) Classical Encryption Techniques : 암호화 기법

1. Crypto

• cryptology : 암호학
• cryptography : make secret code
• cryptanalysis : break secret code
• assumption (Kerckhoffs' principle)ii) crypto algorithm is not secret
• i) only the key is secret

2. Symmetric key crypto

1. Substitution
   • key : n - shift
   • Ceasar's cipher
2. permutation of letters (순열)
   • randomly assigned
   • cipher wheel
3. cryptanalysis
   • using letter frequency statistics
   • Vignere encryption
4. double transposition
   • key = matrix size and permutation

5. one-time pad encryption (vernam cipher)

• key = random pad를 한번만 사용 - 송수신자만 알 수 있음

6. Codebook cipher

• book of random numbers
• usually additive

7. Claude Shannon

• fundamental concept
  • confusion : plain text - cipher text 관계의 모호함 - one time pad
  • diffusion : cipher text를 통해 plain text 통계 분산하여 분석 X - double transposition

3. Taxanomy of cryptography

• symmetric key : 암호화 복호화에 same key 사용
  • stream ciphers
  • block ciphers
• asymmetric cryptography (public key)
  • public key for encryption
  • private key for decryption
  • digital signatures
• hash algorithms
  • one way crypto
  • : just encryption no decryption

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References

• 성균관대학교 소프트웨어학과 타메르 교수님의 <정보보호개론> 수업을 듣고 정리한 내용입니다.