Networking and Cryptography Quiz

The work done by UDP is/are: (A) Congestion control (B) Flow control (C) Retransmission (D) Segments transmission Choose the correct answer from the options given below :

• (A) and (D) Only

• (C) Only

• (D) Only

• (B) and (C) Only

Answer explanation

UDP (User Datagram Protocol) is a simple, connectionless protocol. It does not perform congestion control, flow control, or retransmission. Its primary function is to transmit data segments, with minimal overhead for faster data transfer. This makes UDP suitable for applications that prioritize speed over reliability, such as video streaming or online gaming.

Hash functions are used to produce the message digests which are then encrypted with a private key to get:

• Public key

• Digital signature

• Cipher text

• Data Encryption Standard

Answer explanation

Hash functions generate a fixed-size message digest from a larger input message. When this digest is encrypted with a private key, it forms a digital signature. This digital signature ensures the authenticity and integrity of the message, as it can be verified using the sender's public key but cannot be forged without the private key.

A message is encrypted using public key cryptography to send a message from sender to receiver. Which one of the following statements is true?

• Receiver decrypts using his own public key

• Receiver decrypts using sender's public key

• Sender encrypts using his own public key

• Sender encrypts using receiver's public key

Answer explanation

In public key cryptography, the sender encrypts the message using the receiver's public key, ensuring that only the receiver, who has the corresponding private key, can decrypt and read the message. This ensures the confidentiality of the message.

Which of the following is not needed by an encryption algorithm used in Cryptography? A) KEY B) Message C) Ciphertext D) User details

• (C) only

• (D) only

• (B), (C) and (D) only

• (C) and (D) only

Answer explanation

An encryption algorithm requires a key (A) and a message (B) as inputs to perform encryption. Ciphertext (C) is the output of the encryption process, not an input, so it is not directly needed for the algorithm to work.User details (D) are not needed by the encryption algorithm. The encryption algorithm works based on the key and message alone. User details are unrelated to the encryption process itself.

Decrypt the message "WTAAD" using the Caesar Cipher with key=15.

• LIPPS

• HELLO

• OLLEH

• DAATW

Answer explanation

In the Caesar Cipher, each letter is shifted by a certain number of positions in the alphabet. Here, the key is 15, meaning each letter in the ciphertext is shifted back by 15 positions.

W= 23-15 = 8 (h)

T = 20-15 = 5 (e)

A = 1-15= -14 + 26 = 12 (1) {when get negative number then add 26 to wrap arround}

A = 1-15 = -14 + 26 = 12 (1)

D = 4-15 =  -11 + 26 = 15 (0)

The ability to inject packets into the internet with a false source address is known as:

• Man-in-the-Middle attack

• IP phishing

• IP sniffing

• IP Spoofing

Answer explanation

IP spoofing is a technique where an attacker manipulates the source address of IP packets to appear as if they are coming from a trusted source. This is often used in network attacks to bypass security filters or to masquerade as another device.

A fully connected network topology is a topology in which there is a direct link between all pairs of nodes. Given a fully connected network with n nodes, the number of direct links as a function of n can be expressed as:

• n(n+1)/2

• (n+1)/2

• n/n/2n/2

• n(n−1)/2

Answer explanation

In a fully connected network, each node is directly connected to every other node. For n nodes, the number of direct links needed is calculated as n(n−1)/2. This is because each of the n nodes can connect to (n−1) other nodes, but each connection is counted twice (once from each node), so we divide by 2.

Which of the following is not a field in TCP header?

• Sequence Number

• Checksum

• Fragmentation Offset

• Window Size

Answer explanation

• The TCP header does not include a fragmentation offset field. Fragmentation is handled by the IP layer, where the header contains fields such as the total length, identification, flags, and fragment offset. The TCP header includes fields like sequence number, checksum, and window size.

In the TCP/IP model, encryption and decryption are functions of layer?

• Data link

• Network

• Transport

• Application

Answer explanation

Encryption and decryption typically occur at the Application layer in the TCP/IP model. While the Data Link layer can provide encryption in some network protocols (like WPA for Wi-Fi), encryption and decryption for general data transfer are commonly handled by application-level protocols such as HTTPS (which uses SSL/TLS), which are responsible for securing data before transmission.

What is the name of the protocol that allows a client to send a broadcast message with its MAC address and receive an IP address in reply?

• ARP

• DNS

• RARP

• ICMP

Answer explanation

RARP (Reverse Address Resolution Protocol) is used by a client to send a broadcast message with its MAC address and receive its corresponding IP address in reply. This is typically used in situations where the client does not have an IP address but knows its MAC address (such as in diskless workstations).