2. CHAPTER 8: SECURITY IN COMPUTER NETWORKS Encryption Encryption Authentication Authentication E-Mail Security E-Mail Security Secure Sockets Layer Secure Sockets Layer IP Security IP Security Wireless Security Wireless Security

3. ENCRYPTION Page 193Chapter 8CS 447 The ease of access provided by most Medium Access Control protocols makes it essential that security measures be taken to protect messages from unauthorized access. The most common security technique in modern network protocols is public key encryption. Each user is provided with two “keys”, complex mathematical algorithms that, when applied individually to a message, will encrypt the message and that, when applied together (in either order) to a message, will restore the original message. Each user makes one of the keys publicly available for anyone to use, and the other is kept private by the user. To ensure that only the receiver can read a message, the sender encrypts that message with the receiver’s public key, which only the receiver’s private key can decrypt.

4. AUTHENTICATION Page 194Chapter 8CS 447 Another aspect of security that concerns network users is authentication, ensuring that the sender of a received message is actually correctly identified. Public and private keys may be used to implement this, too. The sender applies his own private key to the outgoing message and the receiver applies the sender’s public key to the message to restore it. Since only a message that was encoded with the sender’s private key (which only the sender possesses) could be decoded with the sender’s public key, the receiver is assured that the appropriate sender transmitted the message.

5. DOUBLE PROTECTION Page 195Chapter 8CS 447 To implement both security and authentication, the sender may apply his own private key and then the receiver’s public key. The receiver will take the received message and apply his private key to it, knowing that his unique ability to do so is what guarantees security. The receiver will apply the sender’s public key to what’s left, knowing that the resulting mesage will only make sense if it actually came from the designated sender.

6. PRIVACY Page 196Chapter 8CS 447 Applying cryptographic algorithms to electronic mail, systems like PGP (Pretty Good Privacy) have been developed to improve e-mail security.

7. SECURE SOCKETS LAYER (SSL) Page 197Chapter 8CS 447 SSL (like its successor, TLS - Transport Layer Security) combines encryption and authentication to provide secure communication for IP data transfers (e.g., Web browsing, e- mail, instant messaging, IP fax)

8. IP SECURITY (IPSEC) Page 198Chapter 8CS 447 IPv4 uses the Encapsulating Security Payload (ESP) technique to add encryption and authentication to its datagrams via its optional header approach (IPv6 requires its use).

9. WI-FI PROTECTED ACCESS (WPA) Page 199Chapter 8CS 447 The IEEE 802.11i standard was developed to address the various threats against wireless LAN security.

10. ESTABLISHING SECURE WPA CONNECTIONS Page 200Chapter 8CS 447 1.The access point periodically transmits a beacon through which it is located and identified by the wireless station. 2.Using an authentication key stored in the station and the authentication server, the station proves its identity. 3.Once authenticated, the station and the authentication server derive cryptographic keys to enable secure communication. 4.Using negotiated encryption/ authentication techniques, data is transferred to the access point, decrypted, and then forwarded to the destination station. 5.Deauthentication and key destruction occur when the wireless connection ends.