network security and cryptography notes

What Are The Network Security And Cryptography Notes?

What are the network security and cryptography notes? These are the notes for A+ Network Security and Cryptography. Is this helpful for the network? Learn more here. 

What are the Network Security And Cryptography Notes?

Network security is the protection of computer networks and the information stored on them from unauthorized access and attacks. 

The three main goals of network security are confidentiality, data integrity, and availability. 

Network security primarily deals with problems caused by unauthorized access to systems or their data, or by the malfunction or malicious behavior of systems and their users. 

The term network security is generally in contrast to computer security, which is to secure an entire computer system. 

Network security deals with computer networking issues such as Internet Protocol (IP) security, Domain Name System (DNS) security, and authentication of users.

It is important to protect information from unauthorized access or modification. This can be in a centralized manner on servers or decentralized on each client’s computer. 


In a centralized system, the sensitive data is encrypted and decrypted by a single trusted entity, usually the service provider. 

The more decentralized approach is to encrypt all the data at the client end, commonly using a public-key algorithm. Also, it is to ensure that no one but the intended recipient can decrypt the message. In this case, the encryption key is only by the end-user. 

The problem with this approach is that it does not scale well (since everyone has to share their key with all parties). Also, it is not secure against an attack where an attacker impersonates a recipient.

To address the scalability problem, a hybrid solution is by many systems. In this case, some of the data is on the server encrypted by a public-key algorithm, and some at the client are by the asymmetric key algorithm (which only the user knows). 


There are two solutions to this problem. The first, called “public-key cryptography”, is the use of two separate encryption keys for messages. 

The sender uses one key to encrypt the message, and the receiver uses the other key to decrypt it. Encryption using one key can be only if the other key is known, and thus both keys are “public”. 

If the two keys are different, it is computationally infeasible to derive one key from the other. This scheme is in all modern encryption methods, including those used for Internet security and PGP. 

The second solution is “symmetric-key cryptography” and is on a single key, kept secret by both the sender and receiver. 

In this case, the sender uses the secret key to encrypt a message, and the receiver uses the same key to decrypt it. 

Main Problem

The main problem with symmetric-key cryptography is key distribution. How can you be sure that a third party has not intercepted your secret key? 

Cryptographic hash functions can be to solve this problem. A hash function produces a fixed-size output for every possible input size and is easy to compute. 

But it is computationally infeasible (i.e. takes an impractically long time) to find a message that corresponds to a given output or to find two different messages with the same hash output. 


In conclusion, network security and cryptography notes are the studies of network security and cryptography. These are useful for a network.