CHAPTER 8: SECURITY IN COMPUTER NETWORKS. Encryption Authentication E-Mail Security Secure Sockets Layer IP Security Wireless Security. ENCRYPTION.
SECURITY IN COMPUTER NETWORKS
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.
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.
To implement both security and authentication, the sender may apply his own private key and then the receiver’s public key.
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.
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.
Applying cryptographic algorithms to electronic mail, systems like PGP (Pretty Good Privacy) have been developed to improve e-mail security.
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)
SSL Change Cipher
Establishes secure connection by exchanging authentication & encryption keys
Signals the end of the key exchange and the start of the actual use of the authentication and encryption
Indicates errors in SSL handshake process
SSL Record Protocol
Once the SSL connection is established, the application data is reformatted into SSL records (packets)
TCP (or other reliable Transport Layer)
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).
The IEEE 802.11i standard was developed to address the various threats against wireless LAN security.