1. Network Security Chapter 8 roadmap 8.1 What is network security? 8.2 Principles of cryptography (confidentiality) 8.3 Message integrity 8.4 End-point authentication 8.5 Securing e-mail (application) 8.6 Securing TCP connections: SSL (transport) 8.7 Network layer security: IPsec (network) 8.8 Securing wireless LANs (MAC) 8.9 Operational security: firewalls and IDS

2. Network Security Secure e-mail  Alice wants to send secure e-mail, m, to Bob  confidentiality  sender authentication  message integrity  receiver authentication Confidentiality  Symmetric key  key distribution issue  public key encryption  but not efficient for long messages  (symmetric, private) session key

3. Network Security Secure e-mail (confidentiality) Alice:  generates random symmetric private session key, K S  encrypts message with K S (for efficiency)  also encrypts K S with Bob’s public key  sends both K S (m) and K B (K S ) to Bob  Alice wants to send confidential e-mail, m, to Bob. K S ( ). K B ( ). + + K S (m ) K B (K S ) + m KSKS KBKB + Internet KSKS

4. Network Security Secure e-mail (confidentiality) Bob:  uses his private key to decrypt and recover K S  uses K S to decrypt K S (m) to recover m  Alice wants to send confidential e-mail, m, to Bob. K S ( ). K B ( ). + + - K S (m ) K B (K S ) + m KSKS KSKS KBKB + Internet K S ( ). K B ( ). - KBKB - KSKS m K S (m ) K B (K S ) +

5. Network Security Secure e-mail (auth. + msg integrity) Alice wants to provide sender authentication & message integrity (but no confidentiality)  Alice digitally signs message (digital signature)  sends both message (in the clear) and digital signature H( ). K A ( ). - + - H(m ) K A (H(m)) - m KAKA - Internet m K A ( ). + KAKA + K A (H(m)) - m H( ). H(m ) compare

6. Network Security Secure e-mail (all)  Alice wants to provide confidentiality, sender authentication, and message integrity. Alice uses three keys: her private key, Bob’s public key, newly created symmetric key H( ). K A ( ). - + K A (H(m)) - m KAKA - m K S ( ). K B ( ). + + K B (K S ) + KSKS KBKB + Internet KSKS

7. Network Security Secure e-mail (all)  Alice wants to provide confidentiality, sender authentication, and message integrity. Alice uses three keys: her private key, Bob’s public key, newly created symmetric key H( ). K A ( ). - + K A (H(m)) - m KAKA - m K S ( ). K B ( ). + + K B (K S ) + KSKS KBKB + Internet KSKS

8. Network Security Secure e-mail (all) Alice and Bob to obtain each other’s public keys!  certify public keys using CA (CA-signed certificates)  receiver authentication