System Security: Cryptography Technologies

1. System Security:Cryptography Technologies CPE 261403 - Operating Systems http://www.e-cpe.org/moodle

2. What does the fish mean?

3. Ichthys

5. User name / Password

6. Threat Ex: Wifi Packet Sniffers

7. Protection with Cryptography

8. Encryption and Decryption • Symmetric – Uses a shared key • Asymmetric – Added security with Public and Private keys

9. Symmetric Encryption Simple example: Add a constant to the ASCII value I LOVE YOU J MPWF ZPV Key = 1

10. Some Examples • Data Encryption Standard (DES) • 56 bit key for every 64 bit value • Advanced Encryption Standard (AES) • 256 bit key for every 128 bit value • RC4 • As used in WEP (Wired Equivalent Privacy) • WPA, WPA2 (Wi-Fi Protected Access) • 256 bit key

11. Asymmetric Encryption

12. Algorithm Example Public Key = (kd, N) Private Key = (ke, N) • N = p.q (where p, q are prime numbers) • Pick kd that is < N • Calculate ke where • ke.kd mod (p-1)(q-1) = 1

13. Example • If p = 7 and q = 13 • N = 7.13 = 91 • Pick Kd = 5 • Find Ke • Ke.5 mod (7-1)(13-1) = 1 • Ke = 29 Public Key = (5, 91) Private Key = (29, 91)

14. Encrypting and Decrypting • Encrypt message = (input ^ ke ) mod N • Decrypt message = (input ^ kd) mod N • If we want to send the number 69 • Encrypted message = 69 ^ 5 mod 91 = 62 • Decrypted message = 62 ^ 29 mod 91 = 69 • *Note: number must < N

15. Notes • In reality p and q can be 512 bits each