Network Security and Cryptography (Firewall, IDS, IPS) : MCQs & PYQs with Explanation

Option A

AES (Advanced Encryption Standard) is a symmetric key encryption algorithm, meaning the same secret key is used for both encryption and decryption. 
When secure communication is required between two persons, they must share a unique secret key. If every pair of users uses a different key, then the total number of keys required equals the number of unique pairs that can be formed among the users. For n persons, the number of such pairs is n(n−1)/2.
For 16 persons, the required keys are 16*15/2=120. Therefore, 120 unique keys are needed so that each pair of persons can communicate securely using AES.

COMPARISON WITH ASYMMETRIC ENCRYPTION:

FOR 16 USERS:

• AES (Symmetric) : 16*15/2 = 120 Keys.
• RSA (Asymmetric) : 2*16 = 32 Keys.

Option B

The primary advantage of setting up a DMZ (Demilitarized Zone) using a firewall is to create multiple zones of trust within a network, which enhances security. A DMZ acts as a buffer zone between the public Internet and the internal private network, isolating public-facing servers (such as web, email, and DNS servers) from sensitive internal resources. This setup allows external users to access services in the DMZ while preventing direct access to the internal network.

Option D

Option B

The SHA-2 (Secure Hash Algorithm 2) family is a set of cryptographic hash functions designed to provide secure hashing for data integrity and digital signatures. 
SHA-2 includes variants such as SHA-224, SHA-256, SHA-384, and SHA-512, where the number in the name indicates the length of the hash output in bits.
SHA-256, the most commonly used variant, produces a 256-bit (32-Byte) hash value.

Option C

The RSA (Rivest Shamir Adleman) is not a data storage algorithm. It is a public-key cryptographic algorithm used for encryption and secure data transmission.
It works on the concept of two keys, a Public Key which is used for encryption and a Private Key which is used for decryption. The security of RSA is based on the mathematical difficulty of factorizing large prime numbers.
RSA is commonly used in Digital Signatures, Secure Web Communication (HTTPS), and Key Exchange mechanisms.

Option C

Data Encryption Standard (DES) is a symmetric key block cipher widely used for secure data transmission. 

• In DES, the input block size is 64 bits, meaning the plaintext is divided into 64-bit blocks before encryption. 
• The key size is 56 bits, although the original key is 64 bits long, 8 bits are used for parity and do not contribute to the actual encryption. 
• The output block size is also 64 bits, so each 64-bit plaintext block is transformed into a 64-bit ciphertext block. 

This design allows secure encryption and decryption using the same 56-bit key.
 

Option D

In cryptography, when a readable message (Plain Text) is converted into an unreadable form using an encryption algorithm and a key, the result is called Cipher Text.

Option A

By default, IIS (Internet Information Services) allows users to access web content without requiring credentials. This is called Anonymous Authentication, where the server uses a built-in account to handle requests from unauthenticated users.

Option A

In information security, different mechanisms are used to achieve different goals.

• Authentication ensures that the identity of a user or system is verified, which is commonly done using a Digital Certificate issued by a trusted authority.
• Non-Repudiation ensures that a sender cannot deny sending a message, and this is achieved through Digital Signing.
• Confidentiality ensures that data remains secret, which is done using Encryption.

Option A

A Honeypot is a special security system used in cyber security to trap and monitor attackers. It acts as a fake or decoy system designed to appear valuable to hackers.
The main purpose of a honeypot is:

• To attract attackers.
• Observe their activities.
• Study hacking methods.
• Improve system security.

A honeypot does not contain important real data. Instead, it is intentionally created to detect unauthorized access attempts.

Option B

Data Encryption Standard (DES) is a Symmetric Key block cipher algorithm that uses the same secret key for both encryption and decryption.

• In DES, the input block size is 64 bits, meaning the plaintext is divided into 64-bit blocks before encryption. 
• The key size is 56 bits, although the original key is 64 bits long, 8 bits are used for parity and do not contribute to the actual encryption. 
• The output block size is also 64 bits, so each 64-bit plaintext block is transformed into a 64-bit ciphertext block. 

The encryption process in DES consists of a series of operations known as rounds. In DES total 16 rounds are performed, making the encryption much stronger and harder to break through Brute-Force or Statistical Attacks.

Option C

In cryptography, cipher modes are techniques used to repeatedly apply a block cipher algorithm for encrypting large amounts of data securely. Common cipher modes are:

• Electronic Code Book (ECB) Mode.
• Cipher Feedback (CFB) Mode.
• Cipher Block Chaining (CBC) Mode.
• Output Feedback (OFB) Mode.
• Counter (CTR) Mode.

However, Stem Cipher Mode is not a standard cipher mode in cryptography.

Option D

A Firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predefined security rules. Its main purpose is to protect a computer network from unauthorized access through the network.
Network Scanning is a technique used by attackers to identify open ports, active hosts, and running services in a network to find vulnerabilities. A properly configured firewall can block suspicious requests, restrict unauthorized access to ports, and prevent scanning attempts, thereby protecting the system from such attacks.

• Dumpster Diving involves retrieving sensitive information from discarded materials such as printed documents.
• Physical Theft refers to stealing hardware like computers or storage devices.
• Shoulder Surfing occurs when someone observes a user entering passwords or confidential information.

Option A

Given, Plaintext = SACKGAUL, but it says read from right to left, so we reverse it: LUAGKCAS. Now, the positions are:

Option D

Fabrication refers to creating fake messages or data, so authentication mechanisms are used to detect and prevent this.
Modification means altering messages during transmission. Ensuring message integrity detects such tampering.
Interception refers to unauthorized access or eavesdropping. Confidentiality (encryption) protects the message content.