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Information system security it346 wk4-1
This document discusses symmetric and asymmetric key cryptography. It explains that symmetric key cryptography uses the same key for encryption and decryption, while asymmetric key cryptography uses public and private key pairs. Stream ciphers and block ciphers are types of symmetric key cryptography. Stream ciphers encrypt plaintext bit-by-bit using a pseudorandom keystream. The document then covers asymmetric key algorithms like RSA, which uses a public key to encrypt and a private key to decrypt. It provides examples of generating and using RSA public and private key pairs to encrypt and decrypt messages.
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Information system security it346 wk4-1
- 1. IT346 Information System Security Week4-1: Stream Cipher & Asymmetric Key Cryptography Faculty of Information Technology Page 1
- 2. Symmetric Key Cryptography Cryptography Symmetric Key Plaintext (BlockCipher) ‣ • 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 2
- 3. Stream Ciphers bit ‣ Key ‣Keystream bit (Stream) Keystream Stream Cipher pseudorandom keystream ‣ Pseudorandom Faculty of Information Technology Page 3
- 4. Stream Ciphers bit ( Keystream XOR) bit random keystream plaintext plaintext Keystream C =P XOR plaintext StreamKey Key encrypt i Faculty of Information Technology i i Page 4
- 5. Stream Ciphers Secret Key Seed Keystream Key StreamCipher 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 5
- 6. 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 6
- 7. Stream Cipher Properties Encryption ‣ ‣ Keystream random StreamCipher random ‣ Secret Key Brute-force Attack bits Faculty of Information Technology Page 7
- 8. RC4 RC4 Stream Cipher RonRivest RSA Security (Security Company) Key (variable key size) (Byte-oriented Stream Cipher) random permutation RC4 SSL/TLS wireless WEP Faculty of Information Technology Page 8
- 9. 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 9
- 10. Asymmetric Key Cryptography (Public Key Cryptography) Facultyof Information Technology Page 10
- 11. Asymmetric Key Cryptography encrypt ‣ ‣ ‣ symmetric keycryptography key decrypt key Key Key key ‣ ciphertext Faculty of Information Technology Symmetric Key Encryption Page 11
- 12. Asymmetric Key Cryptography cryptosystem cryptography ‣ PublicKey asymmetric key key key ‣ Private Key key Encryption ‣ public key encrypt Faculty of Information Technology public key Page 12
- 13. Asymmetric Key Cryptography Faculty ofInformation Technology Page 13
- 14. Asymmetric Encryption Public-Key Cryptosystem ‣ encrypt ciphertext decrypt plaintextP = 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 14
- 15. Public Key Cryptography PublicKey Cryptography one-way function ‣ One-Way Function (Multiplication) (Factorization) ‣ • x12 = 144 • x12 144 = 12x12 = 144x1 = 24x6, … Faculty of Information Technology Page 15
- 16. Symmetric Key Cryptography Asymmetric Key Cryptography ‣ SecurityGoals Confidentiality, Integrity, Authenticity, Av ailability Non-Repudiation ‣ Faculty of Information Technology Page 16
- 17. RSA Algorithm Diffie-Hellman Algorithm ( Key Exchange) Elliptic Curve Cryptography Digital Signature Algorithm Faculty of Information Technology Page 17
- 18. RSA RSA Adi Shamir) LenAdleman) MIT Faculty of Information Technology Ron Rivest) RSA Page 18
- 19. RSA (prime number) p q ‣ gcd ‣ Facultyof Information Technology n = pq m = (p-1)(q-1) e 1<e<m e m e e m gcd(e, m) Page 19
- 20. 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 20
- 21. 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 21
- 22. 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 5 E 10 Faculty of Information Technology Page 22