Week 4 – CST– 311 Intro to Computer Networks

Module 4 –Security in Computer Networks

This week we covered Network Security. With secure communication, the goal is to achieve confidentiality, message integrity, end-point authentication, and operational security. Confidentiality means that only the sender and the intended receiver should be able to understand the contents of the transmitted message. Message integrity ensures that the content of the messages is not altered on purpose or by accident during transit. End-point authentication allows the sender and receiver to confirm the identity of the party with which they are communicating. Finally, operational security is how users or corporations can counter attacks like depositing worms into the network, obtaining private documents, and launching DoS attacks.

The bulk of this week was focused on cryptography. Cryptography allows the sender to mask the information to prevent intruders from gaining access to the actual information. Plain text is the original form of a message, and an encryption algorithm is used to create an encrypted message called ciphertext. The encryption algorithm uses a key and plain text to produce ciphertext. There are two types of key systems, symmetric and public. With a symmetric key system, the sender and the receiver have identical secret keys. In a public key system, two keys are used. One key is known to both the sender and receiver and the other key is known only to the sender or the receiver.

An example of a symmetric key algorithm is the Caesar cipher. In this algorithm, we take each letter in the plain text message and substitute it for another letter a certain number of letters ahead or behind in the alphabet. For example, if we take the message “computer science” and we use a key (k) that shifts the letters 2 letters forward (k=2), the cyphertext would be “eqorwvgt uekgpeg.” If you are shifting forward, the letters will shift from z to a and from a to z if you are shifting backwards.