1. Security

2. Cryptography (1) Intruders and eavesdroppers in communication.

3. Cryptosystems Symmetric key cryptosystems –Same key is used for encryption and decryption –DES Asymmetric key cryptosystems –Public key and private key –Usage depends on application –RSA Hash functions –Detecting message tampering –MD5

4. Authentication Authentication based on a shared secret key.

5. Efficient Authentication? Authentication based on a shared secret key, but using three instead of five messages.

6. Authentication Using Public-Key Cryptography Mutual authentication in a public-key cryptosystem.

7. Authentication Using a Key Distribution Center (1) Figure 9-15. The principle of using a KDC.

8. Authentication Using a Key Distribution Center (2) Figure 9-16. Using a ticket and letting Alice set up a connection to Bob.