Information system security wk4-cryptography-2
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Information system security wk4-cryptography-2
- 1. IT346 Information System Security Week 4: Cryptography (Continue) Faculty of Information Technology Page
- 2. Cryptography Cryptography graph crypto “ Cryptography Cryptography ” 3 ‣ Symmetric Key Cryptography Key Cryptography ‣ Asymmetric Key Cryptography Key Cryptography Faculty of Information Technology Secret Public Page
- 3. Symmetric Key Cryptography Cryptography Symmetric Key Plaintext (Block Cipher) ‣ • DES: • 3DES: • AES: 1 1 Data Block = 64 bits 1 Data Block = 64 bits 1 Data Block = 128 bits (Stream Cipher) ‣ Faculty of Information Technology Page
- 4. Stream Ciphers bit ‣ Key ‣ Keystream bit (Stream) Keystream Stream Cipher pseudorandom keystream ‣ Pseudorandom Faculty of Information Technology Page
- 5. Stream Ciphers bit ( Keystream XOR) bit random keystream plaintext plaintext Keystream plaintext Key Ci = Pi XOR StreamKeyi encrypt Faculty of Information Technology Page
- 6. Stream Ciphers Secret Key Seed Keystream Key Stream Cipher Pseudorandom K Key K KeyStream Generator (Pseudorandom byte generator) 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. One-Time-Pad (OTP) Stream Cipher One-Time-Pad Cipher break ‣ Keystream Vernam (unbreakable cipher) random number Secret Key Pseudorandom number generator ‣ Secret Key OTP Keystream plaintext OTP Faculty of Information Technology OTP Page
- 8. Stream Cipher Properties Encryption ‣ ‣ Keystream random Stream Cipher random ‣ Secret Key Brute-force Attack bits Faculty of Information Technology Page
- 9. RC4 RC4 Stream Cipher Ron Rivest RSA Security (Security Company) Key (variable key size) (Byte-oriented Stream Cipher) random permutation RC4 SSL/TLS wireless WEP Faculty of Information Technology Page
- 10. RC4 Keystream Generation RC4 state ‣ keystream S secret internal : Permutation bytes ‣ Pointer i j: Pointer S bits Keystream Generation ‣ Key Faculty of Information Technology – S bits Page
- 11. Key Scheduling Algorithm (KSA) KSA S ‣ byte for i from 0 to 255 S[i] S[1] := i endfor S S[0] , , Identity Permutation ‣ for i from 0 to 255 j := (j + S[i] + key[i mod keylength]) mod 256 swap S[i] and S[j] Permute S Key endfor Faculty of Information Technology Page
- 12. Pseudo-Random Generation Algorithm (PRGA) PRGA Keystream ‣ keystream Keystream Faculty of Information Technology byte PRGA Byte encryption Page
- 13. Pseudo-Random Generation Algorithm (PRGA) PRGA pointer i ‣ ‣ i • j • • • (S[i] Faculty of Information Technology S[i] j PRGA S[i] i := 0 , j := 0 S[j] while S[i] S[j] :=GeneratingOutput: i (i + 1) mod 256 Keystream (j + S[i]) mod 256 j := swap S[i] and S[j] S + S[j]) mod K := S[(S[i] + S[j]) mod 256] 256 output K endwhile Page
- 14. Pseudo-Random Generation Algorithm (PRGA) Faculty of Information Technology PRGA Page
- 15. Attack on Cryptography Cryptanalysis plaintext break encrypt ‣ Ciphertext-only attack encrypt Key key ciphertext key ‣ Known-plaintext attack plaintext key key ‣ Chosen-plaintext attack Faculty of Information Technology plaintext ciphertext ciphertext Page 15
- 16. Asymmetric Key Cryptography (Public Key Cryptography) Faculty of Information Technology Page
- 17. Asymmetric Key Cryptography encrypt ‣ ‣ ‣ symmetric key cryptography key decrypt key Key Key key ‣ ciphertext Faculty of Information Technology Symmetric Key Encryption Page 17
- 18. Asymmetric Key Cryptography cryptosystem cryptography ‣ Public Key asymmetric key key key ‣ Private Key key Encryption ‣ public key encrypt Faculty of Information Technology public key Page 18
- 19. Asymmetric Key Cryptography Faculty of Information Technology Page
- 20. Asymmetric Encryption Public-Key Cryptosystem ‣ encrypt ciphertext decrypt plaintext P = Plaintext E(P, PKreceiver) = C ‣ public key private key encryption decryption ‣ Plaintext Faculty of Information Technology E(C, SKreceiver) = P C = Cipherte PK = Public K SK = Private public key private Public Key key Private Key Ciphertext Encryp Decryp tion tion Plaintext Page 20
- 21. Public Key Cryptography Public Key Cryptography one-way function ‣ One-Way Function (Multiplication) (Factorization) ‣ • x12 = 144 • x12 144 = 12x12 = 144x1 = 24x6, … Faculty of Information Technology Page 21
- 22. RSA Algorithm Diffie-Hellman Algorithm ( Key Exchange) Elliptic Curve Cryptography Digital Signature Algorithm Faculty of Information Technology Page 22
- 23. RSA RSA Adi Shamir) Len Adleman) MIT Faculty of Information Technology Ron Rivest) RSA Page 23
- 24. RSA (prime number) p q ‣ gcd ‣ Faculty of Information Technology n = pq m = (p-1)(q-1) e 1<e<m e m e e m gcd(e, m) Page 24
- 25. RSA Encryption M M<n Public Key (e, n) ‣ Ciphertext C = Me mod n RSA Decryption ciphertext C (d, n) ‣ Message Private Key M = Cd mod n ‣ p = 5, q = 7, n = 35, m = 24 Faculty of Information Technology Page 25
- 26. n = 35, e = 5 Ciphertext = Me mod n Plainte M xt L 12 Me O 15 759375 15 V 22 E 5 515363 22 2 3125 10 Faculty of Information Technology 248832 17 Page 26
- 27. n = 35, d = 29 Cd Cipher text 17 15 22 M= Cd mod n Plainte xt 481968572106750915091411 12 82522307000 127834039488589391112327 15 57568359400 L 8.5164331908653770195619 449972111e+38 22 V 5 E 10 Faculty of Information Technology O Page 27