Important Question on Computer Network Security

Data confidentiality refers to protecting data against unintentional, unlawful, or unauthorized access, disclosure, or theft. Confidentiality has to do with the privacy of information, including authorizations to view, share, and use it.
Data security refers to the protection of data against unauthorized access or corruption and is necessary to ensure data integrity. That said, data integrity is a desired result of data security, but the term data integrity refers only to the validity and accuracy of data rather than the act of protecting data.

Active attacks: An Active attack attempts to alter system resources or effect their operations. Active attack involve some modification of the data stream or creation of false statement. Types of active attacks are as following:
1.Masquerade –
Masquerade attack takes place when one entity pretends to be different entity. A Masquerade attack involves one of the other form of active attacks.
2.Modification of messages –
It means that some portion of a message is altered or that message is delayed or reordered to produce an unauthorised effect. For example, a message meaning “Allow JOHN to read confidential file X” is modified as “Allow Smith to read confidential file X”.
3.Repudiation –
This attack is done by either sender or receiver. The sender or receiver can deny later that he/she has send or receive a message. For example, customer ask his Bank “To transfer an amount to someone” and later on the sender(customer) deny that he had made such a request. This is repudiation.
4.Replay –
It involves the passive capture of a message and its subsequent the transmission to produce an authorized effect.
Denial of Service –
It prevents normal use of communication facilities. This attack may have a specific target. For example, an entity may suppress all messages directed to a particular destination. Another form of service denial is the disruption of an entire network wither by disabling the network or by overloading it by messages so as to degrade performance.

Transposition technique in symmetric cipher

Network Security Model And Its Components

A symmetric cipher is one that uses the same key for encryption and decryption. Symmetric ones use the same key (called a secret key or private key) for transforming the original message, called plaintext, into ciphertext and vice versa. Symmetric ciphers are generally faster than their asymmetric counterparts, which use a closely-held private key as well as a public key shared between the two parties (hence public-key cryptography, or PKC). Examples of symmetric ciphers are Advanced Encryption Standard (AES), Data Encryption Standard (DES), Blowfish, and International Data Encryption Algorithm (IDEA).

The DES (Data Encryption Standard) algorithm is a symmetric-key block cipher created in the early 1970s by an IBM team and adopted by the National Institute of Standards and Technology (NIST). The algorithm takes the plain text in 64-bit blocks and converts them into ciphertext using 48-bit keys.
Since it’s a symmetric-key algorithm, it employs the same key in both encrypting and decrypting the data. If it were an asymmetrical algorithm, it would use different keys for encryption and decryption.
DES is based on the Feistel block cipher, called LUCIFER, developed in 1971 by IBM cryptography researcher Horst Feistel. DES uses 16 rounds of the Feistel structure, using a different key for each round.

DES Algorithm Steps
1.To put it in simple terms, DES takes 64-bit plain text and turns it into a 64-bit ciphertext. And since we’re talking about asymmetric algorithms, the same key is used when it’s time to decrypt the text.
2.The algorithm process breaks down into the following steps:
3.The process begins with the 64-bit plain text block getting handed over to an initial permutation (IP) function.
4.The initial permutation (IP) is then performed on the plain text.
5.Next, the initial permutation (IP) creates two halves of the permuted block, referred to as Left Plain Text (LPT) and Right Plain Text (RPT).
6.Each LPT and RPT goes through 16 rounds of the encryption process.
7.Finally, the LPT and RPT are rejoined, and a Final Permutation (FP) is performed on the newly combined block.
The result of this process produces the desired 64-bit ciphertext.
The encryption process step (step 4, above) is further broken down into five stages:
1.Key transformation
2.Expansion permutation
3.S-Box permutation
4.P-Box permutation
5.XOR and swap
For decryption, we use the same algorithm, and we reverse the order of the 16 round keys.