Network Security issues

Network Security refers to the measures taken by any enterprise or organisation to secure its computer network and data using both hardware and software systems. This aims at securing the confidentiality and accessibility of the data and network. Every company or organisation that handles a large amount of data, has a degree of solutions against many cyber threats.

Types of Network Security: 

The few types of network securities are discussed below : 

1. Access Control:
   Not every person should have a complete allowance for the accessibility to the network or its data. One way to examine this is by going through each personnel’s details. This is done through Network Access Control which ensures that only a handful of authorised personnel must be able to work with the allowed amount of resources.
    
2. Antivirus and Anti-malware Software:
   This type of network security ensures that any malicious software does not enter the network and jeopardise the security of the data. The malicious software like Viruses, Trojans, and Worms is handled by the same. This ensures that not only the entry of the malware is protected but also that the system is well equipped to fight once it has entered.
    
3. Cloud Security:
   Nowadays, a lot of organisations are joining hands with cloud technology where a large amount of important data is stored over the internet. This is very vulnerable to the malpractices that few unauthorised dealers might pertain. This data must be protected and it should be ensured that this protection is not jeopardised by anything. Many businesses embrace SaaS applications for providing some of their employees the allowance of accessing the data stored over the cloud. This type of security ensures creating gaps in the visibility of the data. 

Cryptography 

Cryptography refers to the science and art of transforming messages to make them secure and immune to attacks. It is a method of storing and transmitting data in a particular form so that only those for whom it is intended can read and process it. Cryptography not only protects data from theft or alteration but can also be used for user authentication.

Substitution Ciphers

A substitution technique is one in which the letters of plaintext are replaced by other letters or by numbers or symbols. If the plaintext is viewed as a sequence of bits, then substitution involves replacing plaintext bit patterns with ciphertext bit patterns. 

The earliest known use of a substitution cipher and the simplest was by Julius Caesar. The Caesar cipher involves replacing each letter of the alphabet with the letter standing 3 places further down the alphabet. e.g., 

plain text : pay more money 

Cipher text: SDB PRUH PRQHB 

Transposition Ciphers

A more complex scheme is to write the message in a rectangle, row by row, and read the message off, column by column, but permute the order of the columns. The order of columns then becomes the key of the algorithm. 

e.g., plaintext = meet at the school house 

Key = 4 3 1 2 5 6 7 

PT = m e e t a t t

h  e  s  c  h  o  o 

l  h  o  u  s  e 

CT = ESOTCUEEHMHLAHSTOETO 

A pure transposition cipher is easily recognized because it has the same letter frequencies as the original plaintext. The transposition cipher can be made significantly more secure by performing more than one stage of transposition. The result is a more complex permutation that is not easily reconstructed. 

Two fundamental cryptographic principles

1. Encryption

Encryption is to convert the data in some unreadable form. This helps in protecting the privacy while sending the data from sender to receiver. On the receiver side, the data can be decrypted and can be brought back to its original form. The reverse of encryption is called decryption. The concept of encryption and decryption requires some extra information for encrypting and decrypting the data. This information is known as a key. There may be cases when the same key can be used for both encryption and decryption while in certain cases, encryption and decryption may require different keys.

2. Authentication

Authentication ensures that the message originated from the originator claimed in the message. Suppose, Alice sends a message to Bob and now Bob wants proof that the message has been indeed sent by Alice. This can be made possible if Alice performs some action on a message that Bob knows only Alice can do.

3. Integrity

One problem that a communication system can face is the loss of integrity of messages being sent from sender to receiver. This means that Cryptography should ensure that the messages that are received by the receiver are not altered anywhere on the communication path. This can be achieved by using the concept of cryptographic hash.

4. Non Repudiation

What happens if Alice sends a message to Bob but denies that she has actually sent the message? Cases like these may happen and cryptography should prevent the originator or sender to act this way. One popular way to achieve this is through the use of digital signatures.

DES : Data Encryption Standard

The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National Institute of Standards and Technology (NIST).

DES is an implementation of a Feistel Cipher. It uses a 16 round Feistel structure. The block size is 64-bit. DES has an effective key length of 56 bits, since 8 of the 64 bits of the key are not used by the encryption algorithm. General Structure of DES is depicted in the following illustration −

Since DES is based on the Feistel Cipher, all that is required to specify DES is −

• Round function
• Key schedule
• Any additional processing − Initial and final permutation

Initial and Final Permutation

The initial and final permutations are straight Permutation boxes (P-boxes) that are inverses of each other. They have no cryptography significance in DES. 

Round Function

The heart of this cipher is the DES function, f. The DES function applies a 48-bit key to the rightmost 32 bits to produce a 32-bit output.

Key Generation

The round-key generator creates sixteen 48-bit keys out of a 56-bit cipher key. 

Digital Signature

The Digital Signature is a technique which is used to validate the authenticity and integrity of the message. We know that there are four aspects of security: privacy, authentication, integrity, and non-repudiation.

The basic idea behind the Digital Signature is to sign a document. When we send a document electronically, we can also sign it. We can sign a document in two ways: to sign a whole document and to sign a digest.

• In Digital Signature, a public key encryption technique is used to sign a document. However, the roles of a public key and private key are different here. The sender uses a private key to encrypt the message while the receiver uses the public key of the sender to decrypt the message.
• In Digital Signature, the private key is used for encryption while the public key is used for decryption.
• Digital Signature cannot be achieved by using secret key encryption.

Digital Signature is used to achieve the following three aspects:

• Integrity: The Digital Signature preserves the integrity of a message because, if any malicious attack intercepts a message and partially or totally changes it, then the decrypted message would be impossible.
• Authentication: We can use the following reasoning to show how the message is authenticated. If an intruder (user X) sends a message pretending that it is coming from someone else (user A), user X uses her own private key to encrypt the message. The message is decrypted by using the public key of user A. 
• Non-Repudiation: Digital Signature also provides non-repudiation. If the sender denies sending the message, then her private key corresponding to her public key is tested on the plaintext. If the decrypted message is the same as the original message, then we know that the sender has sent the message.

Firewalls

A firewall is a network security device; it is a protective layer for the server that monitors and filters all the incoming and outgoing network traffic. It uses a set of rules to determine whether to allow or block a specific network traffic. Firewalls can prevent unauthorised use before reaching the servers. Firewalls can be hardware or software-based.

To protect private networks and individual machines, a firewall can be employed to filter incoming or outgoing traffic based on a predefined set of rules known as firewall policies.

Packet flowing through a firewall can have one of the following three outcomes −

• Accepted − Permitted through the firewall.
• Dropped − Not allowed through with no indication of failure
• Rejected − Not allowed through accompanied by an attempt to inform the source that the packet was rejected.

Types of Firewall

• Packet Filters (Stateless Firewall) − In the packet filters, if a packet matches then the packet filters a set of rules and filters will drop or accept it.

• Stateful firewall filters − It is also known as a network firewall; this filter maintains a record of all the connections passing through. It can determine if a packet is either the start of a new connection or a part of an existing connection or is an invalid packet.

Application firewall − A web application firewall is used for HTTP applications. There are sets of rules that are applied to monitor or block data packets from HTTP network traffic. For example, these rules can help block cross-site scripting (XSS) and SQL injections.