Information system security wk4-cryptography-2
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This document discusses cryptography techniques including symmetric key cryptography, stream ciphers, the one-time pad cipher, RC4 stream cipher, and asymmetric key cryptography. Symmetric key cryptography uses the same key for encryption and decryption, while asymmetric key cryptography uses public and private key pairs. Specific techniques covered include DES, AES, RC4 stream cipher, one-time pad, and the RSA algorithm for asymmetric encryption.
![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](https://image.slidesharecdn.com/9164it346-wk4-cryptography-2-131015153818-phpapp01/85/Information-system-security-wk4-cryptography-2-11-320.jpg)
![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](https://image.slidesharecdn.com/9164it346-wk4-cryptography-2-131015153818-phpapp01/85/Information-system-security-wk4-cryptography-2-13-320.jpg)
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