1. Ln Lou 2014.8 Modern Cyphers

2. 0. Security System Key Plain Text Cipher Text Encryption (K × P → C) Decryption (K × C → P)

3. 1. Symmetric Key Algorithm 1.1 Stream Cyphers 1.2 Block Cyphers

4. 1.1 Stream cyphers RC4 (WEP, SSL) Salsa20/12

5. One-time Pad len(m) == len(c) == len(k) D(k, m) = k ⊕ m E(k, c) = k ⊕ c

6. One-time Pad k = 1001110001010111 m = 1100010100101101 c = 0101100101111010 m = 1100010100101101

7. 1.1 Stream Cyphers Pseudorandom Generator (PRG) {0, 1} s → {0, 1} n n >> s Initialization Vector (IV) E(k, m) = m ⊕ PRG(k, IV) D(k, c) = c ⊕ PRG(k, IV)

8. 1.2 Block Cyphers DES 3-DES AES

9. 1.2.1 Mode of Operation ECB CBC CFB CTR

10. 1.2.1.1 ECB

12. 1.2.1.1 EBC

13. 1.2.1.2 CBC C i = E k (P i ⊕ C i-1 ), C 0 = IV

14. 1.2.1.2 CBC P i = D K (C i ) ⊕ C i-1, C 0 = IV

15. 1.2.1.3 CFB C i = E K (C i-1 ) ⊕ P i, C 0 = IV

16. 1.2.1.3 CFB P i = E K (C i-1 ) ⊕ C i, C 0 = IV

17. 1.2.1.4 OFB

19. 1.2.2.1 Iterated Cyphers key k → k 0, k 1, k 2, …, k n round function R m 0 = m m i+1 = R(k i+1, m i ) c = m n

20. 1.2.2.2 SP Network Substitution Permutation

21. 1.2.2.3 Feistel Cypher Encryption: L i+1 = R i R i+1 = L i ⊕ F(K i, R i ) Decryption: R i = L i+1 L i = R i+1 ⊕ F(K i, L i+1 )

22. 2. Asymmetric Key Algorithm Encrypt: public key Decrypt: private key

23. 2.1 RSA Choose n = pq Compute φ(n) = n-(p+q-1) public key e: 1 < e < φ(n) && gcd(e, φ(n)) == 1 private key d: d ≡ e -1 (mod φ(n))

24. 2.1 RSA Encryption: c = m e mod n Decryption: m = c d mod n

25. Reference Wikipedia http://class.coursera.org/crypto-preview