Information system security wk4-cryptography-2

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Information system security wk4-cryptography-2

  1. 1. IT346 Information System Security Week 4: Cryptography (Continue) อ.พงษ์ ศักดิ์ Faculty of Information Technology ไผ่แดง Page
  2. 2. Cryptography ก Cryptography F F F graph Fก F ก F F Cryptography F ก ˂ ก F ก F 3 ก ‣ Symmetric Key Cryptography F F ‣ Asymmetric Key Cryptography F F ‣ Hash Function ก F Faculty of Information Technology ก F crypto Cryptography Secret Key Cryptography ก Public Key Cryptography ก F Page
  3. 3. Symmetric Key Cryptography F ก Cryptography ก Plaintext (Block Cipher) ก F ‣ 1 Symmetric Key F F ˈ ก ก F • DES: 1 Data Block = 64 bits • 3DES: 1 Data Block = 64 bits • AES: 1 Data Block = 128 bits (Stream Cipher) ก F ‣ • RC4 Faculty of Information Technology Page
  4. 4. Stream Ciphers ก ‣ F ˈ ก Key bit ก bit F ก (Stream) F ˈ ‣ Keystream ก keystream ‣ Pseudorandom F กก ก F ก กก Faculty of Information Technology F F F ก ก F Keystream Stream Cipher ˈ pseudorandom F F F F ˈ F F F F Page
  5. 5. Stream Ciphers F bit bit F Keystream ก ก ( F ก XOR) ก random keystream plaintext ( F ก plaintext) F ก F Keystream F Key ก encrypt F F plaintext Ci = Pi XOR StreamKeyi Faculty of Information Technology Page
  6. 6. Stream Ciphers F Secret Key Stream Cipher ก F Pseudorandom Keystream F Seed ˂ Key K Key K KeyStream Generator (Pseudorandom byte generator) Fก KeyStream Generator (Pseudorandom byte generator) Plaintext Byte Stream P + ENCRYPTION Faculty of Information Technology Ciphertext Byte Stream C + Plaintext Byte Stream P DECRYPTION Page
  7. 7. One-Time-Pad (OTP) Stream Cipher F Vernam Cipher) ˈ ก break F (unbreakable cipher) ก One-Time-Pad ( F F F กF ‣ Keystream OTP ˈ random number F F F F F ก Secret Key F Pseudorandom number generator ‣ Secret Key OTP Keystream F F F F F ก plaintext Fก F OTP F ก F ˈ F F F ก Faculty of Information Technology Page
  8. 8. Stream Cipher Properties F ก F Stream Cipher Fก ก Encryption F ˈ F ก กF ก ก ‣ Keystream F F random F ก random ก F F F ‣ Secret Key F ˂ ก Brute-force Attack ก F ก F 128 bits ‣ F F F ก F Block Cipher F ก Stream Cipher F F F ก Block Cipher F Key Fก Faculty of Information Technology ก F F Page
  9. 9. RC4 ก Ron Rivest RC4 ˈ Stream Cipher Security (Security Company) F Key F (variable key size) ก (Byte-oriented Stream Cipher) ก random permutation RC4 ˈ F F F ก กก ก F F SSL/TLS wireless WEP Faculty of Information Technology Fก RSA F Page
  10. 10. RC4 Keystream Generation RC4 F keystream ก secret internal state F F กF ‣ F FS ˈ F ‣ Pointer i ก F: ก F Permutation ( F 256 bytes j: Pointer 8 bits ก ก F 2 F Faculty of Information Technology F S F กF F Key ( ก F 40 256 bits) ก ก F F FS F Key Scheduling Algorithm (KSA) ‣ F FS F ก ก F key stream random generation algorithm (PRGA) ‣ 2 F) 256 Keystream Generation F F Fก F pseudo- Page
  11. 11. Key Scheduling Algorithm (KSA) KSA F ก ก ก ‣ F F Fก F F ก 00000001, ... ) F FS ก F ก กก Fก F F FS ก F ก F byte F ( F S[0] ก 00000000, S[1] ก F F Identity Permutation for i from 0 to 255 S[i] := i endfor ‣ S ก 256 F Key F ก Permute ( F) F for i from 0 to 255 j := (j + S[i] + key[i mod keylength]) mod 256 swap S[i] and S[j] endfor Faculty of Information Technology Page
  12. 12. Pseudo-Random Generation Algorithm (PRGA) PRGA F ก ‣ F byte Keystream Faculty of Information Technology F Keystream ก F ก PRGA ก F ก encryption F keystream ก Fก Byte 1 Page
  13. 13. Pseudo-Random Generation Algorithm (PRGA) PRGA ˈ ก F ‣ ‣ F • • • • F pointer i ก i ( j ( F S[i] S[j] F F Keystream (S[i] + S[j]) mod 256 Faculty of Information Technology j F PRGA F 0 ก F )1 F ก F ) F ก F S[i] F Fก F F F S[i] ก F ก F FS F S[j] F i := 0 , j := 0 while GeneratingOutput: i := (i + 1) mod 256 j := (j + S[i]) mod 256 swap S[i] and S[j] K := S[(S[i] + S[j]) mod 256] output K endwhile Page
  14. 14. Pseudo-Random Generation Algorithm (PRGA) F Faculty of Information Technology ก PRGA Page
  15. 15. Attack on Cryptography ก F F plaintext F F Cryptanalysis ก Key F ˈ ก break ก encrypt F F ˈ 3 ‣ Ciphertext-only attack ciphertext encrypt ก ‣ Known-plaintext attack ก ก ‣ Chosen-plaintext attack ก attacker F F ciphertext Faculty of Information Technology ก key F plaintext ciphertext plaintext F key F ciphertext plaintext ก plaintext ˂ Fก plaintext F ˈ F key F ก ˈ key F ก key ก key F F Page 15
  16. 16. Asymmetric Key Cryptography (Public Key Cryptography) Faculty of Information Technology Page
  17. 17. Asymmetric Key Cryptography F key symmetric key cryptography ก ก encrypt decrypt F ‣ ก F F ˆ ‣ ‣ ‣ ˆ F F F F F F F F ก key กF F F F F ก ก F F Fก กF ก ก ก Key ก ก ก ก Key F ˈ ก F F ก F F F key ก F F ก F F ก F ก F ciphertext ก F F ก Symmetric Key Encryption F non-repudiation Public Key Encryption F key Asymmetric Encryption F ก ก encrypt decrypt F Faculty of Information Technology Page 17
  18. 18. Asymmetric Key Cryptography cryptosystem key 2 F กF ‣ Public Key FF ‣ Private Key F ˁ asymmetric key cryptography ˈ key F ˈ key ก F F ก Encryption ก F ˈ F F F ˁ ˁ ˈ F ‣ F F F public key F ก ˈ F ก F กF F ก encrypt F F public key F F private key Fก ‣ F decrypt F ‣ ก encrypt F F F public key ˈ F F F private key decrypt F Faculty of Information Technology Page 18
  19. 19. Asymmetric Key Cryptography Faculty of Information Technology Page
  20. 20. Asymmetric Encryption Public-Key Cryptosystem ‣ encrypt F plaintext ก ก E(P, PKreceiver) = C F ciphertext decrypt F P = Plaintext C = Ciphertext PK = Public Key SK = Private Key E(C, SKreceiver) = P public key private key decryption F F F ‣ ก ʽ public key ˈ private key Fก F F Public Key ‣ F Plaintext Faculty of Information Technology Encryption Ciphertext F F ก encryption F Private Key Decryption Plaintext Page 20
  21. 21. Public Key Cryptography Public Key Cryptography function ‣ One-Way Function ˆ กF ก F F F F ก F one-way ˈ F ก ก F ‣ ก (Multiplication) • • F F F ก ก F F 12x12 F F F F 144 F กF ก 144 = 12x12 = 144x1 = 24x6, F ก ก F F (Factorization) F F 12x12 = 144 กก ก ก Logarithms ‣ Exponential • F F F 3ก 6 กก • F F F F 729 F ก F ก กก (x=?, y=?) Faculty of Information Technology F FF 36 =729 ก logx 729 = y Page 21
  22. 22. ก F RSA Algorithm Diffie-Hellman Algorithm ( Elliptic Curve Cryptography Digital Signature Algorithm Faculty of Information Technology F ก F Key Exchange) Page 22
  23. 23. RSA F RSA ก Faculty of Information Technology F (Ron Rivest) (Len Adleman) MIT F (Adi Shamir) RSA ก 3 Page 23
  24. 24. ก ก F ก ‣ RSA (prime number) p ก ก F Fก ก ก Fก n = pq m = (p-1)(q-1) ก F e 1<e<m e m ˈ ‣ ก F e q F F ก F ก F ก F ก F F ก (gcd) ก ก F gcd(e, m) ˈ 1 eก m ˈ 1 F d ed mod m = 1 Public Key = F (e, n) Private Key = F (d, n) Faculty of Information Technology Page 24
  25. 25. ก RSA Encryption F ก F F Key (e, n) F ‣ Ciphertext F M F F Public C = Me mod n RSA Decryption ciphertext C ‣ Message M<n ก F Private Key (d, n) F M = Cd mod n F ‣ p = 5, q = 7, n = 35, m = 24 ‣ e = 5, d = 29 Faculty of Information Technology Page 25
  26. 26. F ก F n = 35, e = 5 Plaintext M Me Ciphertext = Me mod n L 12 248832 17 O 15 759375 15 V 22 5153632 22 E 5 3125 10 Faculty of Information Technology Page 26
  27. 27. F ก n = 35, d = 29 Cd Ciphertext M= Cd mod n Plaintext 17 48196857210675091509141182522307000 12 L 15 12783403948858939111232757568359400 15 O 22 8.5164331908653770195619449972111e+38 22 V 10 100000000000000000000000000000 5 E Faculty of Information Technology Page 27

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