Table of Contents
Paper 1: B.Tech 8th Semester Examination, 2024(S)
Subject: Cryptography and Network Security
Q.1 (a) The full form of SSL is: 1
- (i) Serial Session Layer
- (ii) Secure Socket Layer
- (iii) Session Secure Layer
- (iv) Series Socket Layer
- Correct Answer: (ii) Secure Socket Layer
Q.1 (b) In SHA-512, the message is divided into blocks of size ____ bits for the hash computation. 2
- (i) 1024
- (ii) 512
- (iii) 256
- (iv) 2048
- Correct Answer: (i) 1024
Q.1 (c) DES follows: 3
- (i) Hash Algorithm
- (ii) Caesars Cipher
- (iii) Feistel Cipher Structure
- (iv) SP Networks
- Correct Answer: (iii) Feistel Cipher Structure
Q.1 (d) The Secure Electronic Transaction (SET) protocol is used for: 4
- (i) Electronic Cash Payments
- (ii) Cheque Payment
- (iii) Credit Card Payment
- (iv) Payment of Small Amounts for Internet Services
- Correct Answer: (iii) Credit Card Payment
Q.1 (e) SSL provides: 5
- (i) Message Integrity
- (ii) Confidentiality
- (iii) Compression
- (iv) All of the above
- Correct Answer: (iv) All of the above
Q.1 (f) Which of the following is an asymmetric encryption algorithm? 6
- (i) 3-DES
- (ii) RC5
- (iii) IDEA
- (iv) RSA
- Correct Answer: (iv) RSA
Q.1 (g) Block ciphers can be used as stream ciphers in: 7
- (i) ECB Mode
- (ii) CBC Mode
- (iii) CFB & OFB Mode
- (iv) OFB Mode
- Correct Answer: (iii) CFB & OFB Mode
Q.1 (h) In an asymmetric-key cipher, the sender uses the ____ key. 8
- (i) Private
- (ii) Public
- (iii) Both (i) and (ii)
- (iv) Either (i) and (ii)
- Correct Answer: (ii) Public(Note: In the context of encryption for confidentiality, the sender uses the receiver’s public key.)
Q.1 (i) The ____ method provides a one-time session key for two parties. 9
- (i) Diffie-Hellman
- (ii) RSA
- (iii) DES
- (iv) AES
- Correct Answer: (i) Diffie-Hellman
Q.1 (j) While creating a digital envelope, we encrypt the one-time session key with: 10
- (i) Receiver’s Public Key
- (ii) Receiver’s Private Key
- (iii) Sender’s Public Key
- (iv) Sender’s Private Key
- Correct Answer: (i) Receiver’s Public Key
Paper 2: B.Tech 6th Semester Examination, 2024
Subject: Cryptography and Network Security
Q.1 (a) Which of the following is not a part of the OSI Security Architecture? 11
- (i) Security Services
- (ii) Security Mechanisms
- (iii) Security Applications
- (iv) Security Attacks
- Correct Answer: (iii) Security Applications
Q.1 (b) What is the primary purpose of steganography? 12
- (i) Encrypting data
- (ii) Hiding the existence of data
- (iii) Decrypting data
- (iv) Generating random numbers
- Correct Answer: (ii) Hiding the existence of data
Q.1 (c) Which technique is used to break the Data Encryption Standard (DES) using a known plaintext attack? 13
- (i) Differential Cryptanalysis
- (ii) Linear Cryptanalysis
- (iii) Brute Force Attack
- (iv) Side-channel Attack
- Correct Answer: (ii) Linear Cryptanalysis
Q.1 (d) In the context of block cipher modes of operation, what does CBC stand for? 14
- (i) Cipher Block Chain
- (ii) Code Block Chain
- (iii) Cipher Block Chaining
- (iv) Code Block Chaining
- Correct Answer: (iii) Cipher Block Chaining
Q.1 (e) Which of the following is an example of a finite field of the form GF(p)? 15
- (i) GF(2^8)
- (ii) GF(19)
- (iii) GF(2^16)
- (iv) GF(31)
- Correct Answer: (ii) GF(19)(Note: GF(31) is also a valid prime field, but GF(19) is the first valid option presented).
Q.1 (f) What does Euclid’s Algorithm compute? 16
- (i) The least common multiple of two numbers
- (ii) The greatest common divisor of two numbers
- (iii) The sum of two numbers
- (iv) The product of two numbers
- Correct Answer: (ii) The greatest common divisor of two numbers
Q.1 (g) What is the main feature of the Advanced Encryption Standard (AES) compared to DES? 17
- (i) Fixed block size of 64 bits
- (ii) Variable key length (128, 192, or 256 bits)
- (iii) Use of Feistel network
- (iv) Use of substitution-permutation network
- Correct Answer: (iv) Use of substitution-permutation network
Q.1 (h) Which encryption method is used in Triple DES? 18
- (i) Encrypt-decrypt-encrypt with the same key
- (ii) Encrypt-encrypt-encrypt with the same key
- (iii) Encrypt-decrypt-encrypt with three different keys
- (iv) Encrypt-decrypt-encrypt with two keys
- Correct Answer: (iv) Encrypt-decrypt-encrypt with two keys(Note: Triple DES can use two or three keys; options (iii) and (iv) are both technically valid modes, but 2-key 3DES is a very common exam standard).
Q.1 (i) Which theorem is used in the RSA algorithm for encryption and decryption? 19
- (i) Fermat’s Little Theorem
- (ii) Euler’s Theorem
- (iii) Chinese Remainder Theorem
- (iv) Pythagorean Theorem
- Correct Answer: (ii) Euler’s Theorem
Q.1 (j) What is the main principle behind public-key cryptosystems? 20
- (i) Use of a single key for encryption and decryption
- (ii) Symmetric encryption
- (iii) Use of two keys, one for encryption and one for decryption
- (iv) Key exchange protocol
- Correct Answer: (iii) Use of two keys, one for encryption and one for decryption
Paper 3: B.Tech 6th Semester Exam, 2022 (New Course)
Subject: Cryptography and Network Security
Q.1 (a) Advanced Encryption Standard (AES) has three different configurations with respect to number of rounds and: 21212121
- (i) data size
- (ii) round size
- (iii) key size
- (iv) encryption size
- Correct Answer: (iii) key size
Q.1 (b) Which of the following is also known as key exchange algorithm? 22
- (i) RSA
- (ii) DES
- (iii) DH
- (iv) ECC
- Correct Answer: (iii) DH (Diffie-Hellman)
Q.1 (c) RC4 is an example of: 23
- (i) hash algorithm
- (ii) stream cipher
- (iii) block cipher
- (iv) None of the above
- Correct Answer: (ii) stream cipher
Q.1 (d) Hash function is: 24
- (i) used to produce fingerprint of a file
- (ii) useful for message authentication
- (iii) Both (i) and (ii)
- (iv) None of the above
- Correct Answer: (iii) Both (i) and (ii)
Q.1 (e) Which one of the following is not a higher-layer SSL protocol? 25
- (i) Alert protocol
- (ii) Handshake protocol
- (iii) Alarm protocol
- (iv) Change cipher spec protocol
- Correct Answer: (iii) Alarm protocol(Note: The correct name is “Alert Protocol”).
Q.1 (f) An HTTP connection uses port ___ whereas HTTPS uses port ___ and invokes SSL. 26
- (i) 40; 80
- (ii) 60; 620
- (iii) 80; 443
- (iv) 620; 80
- Correct Answer: (iii) 80; 443
Q.1 (g) The DES algorithm cipher system consists of ___ rounds (iterations) each with a round key. 27
- (i) 12
- (ii) 18
- (iii) 9
- (iv) 16
- Correct Answer: (iv) 16
Q.1 (h) For $p=11$ and $q=19$ and choose $e=17$. Apply RSA algorithm where message = 5 and find the cipher text. 28
- (i) C=80
- (ii) C=92
- (iii) C=56
- (iv) C=23
- Correct Answer: (i) C=80
Q.1 (i) SHA-1 produces a hash value of: 29
- (i) 256 bits
- (ii) 160 bits
- (iii) 180 bits
- (iv) 128 bits
- Correct Answer: (ii) 160 bits
Q.1 (j) In which of the following encryption key is used to encrypt and decrypt the data? 30
- (i) Public key
- (ii) Private key
- (iii) Symmetric key
- (iv) Asymmetric key
- Correct Answer: (iii) Symmetric key
Paper 4: B.Tech Special Examination, 2023
Subject: Cryptography and Network Security
Source: 135, 136
Q.1 (a) What are the requirements of Encrypted Tunnels?
Answer:
Encrypted tunnels require:
- Confidentiality – Data should not be readable by unauthorized users.
- Data Integrity – Data should not be modified in transit.
- Authentication – Both ends must verify each other to prevent impersonation.
Q.1 (b) Explain Transport Layer Security (TLS)?
Answer:
TLS is a cryptographic protocol that secures communication over the internet. It is the upgraded version of SSL and provides privacy, authentication, and data integrity between client and server applications.
Q.1 (c) Why compression is done before encryption in PGP?
Answer:
Compression is done before encryption because:
- It reduces message size for quick transmission.
- It removes redundancy, making cryptanalysis attacks (like frequency analysis) more difficult.
Q.1 (d) What do you mean by cryptanalysis?
Answer:
Cryptanalysis is the method of breaking cryptographic codes and ciphers to obtain the original message without knowing the key. It studies weaknesses in algorithms.
Q.1 (e) Define Euler’s theorem and its application.
Answer:
Euler’s theorem states:
If a and n are positive integers and coprime, then
a raised to the power phi(n) gives remainder 1 when divided by n.
It is mainly used in RSA encryption, especially in key generation.
Q.1 (f) Between symmetric and asymmetric encryption which method is more convenient and why?
Answer:
Symmetric encryption is more convenient for encrypting large data because it is faster and requires less computation.
Asymmetric encryption is more convenient for secure key distribution and authentication.
Q.1 (g) Define block cipher.
Answer:
A block cipher encrypts data in fixed-size blocks (such as 64 or 128 bits). The output block length is the same as the input block length.
Q.1 (h) Differentiate between public key and private key.
Answer:
- Public Key: Shared openly, used to encrypt data or verify signatures.
- Private Key: Kept secret, used to decrypt data or create signatures.
Q.1 (i) What do you mean by cryptography?
Answer:
Cryptography is the science of protecting information using techniques like encryption and decryption. It ensures confidentiality, integrity, and authentication.
Q.1 (j) Describe birthday attack.
Answer:
A birthday attack exploits the probability theory of the birthday paradox to find two different inputs that generate the same hash (collision). It is mainly used to attack hash functions.
Paper 5: B.Tech End Semester Examination, 2022
Subject: Cryptography and Network Security
Source: 296
Q.1 (a) Why network need security?
Answer:
Networks need security to ensure:
- Confidentiality – Data remains secret.
- Integrity – Data is not tampered with.
- Availability – Network services remain usable.
- Authentication – Verifying user identity.
Q.1 (b) Compare substitution and transposition techniques.
Answer:
- Substitution: Each character is replaced by another character, number, or symbol.
- Transposition: The positions of characters are rearranged without changing the characters themselves.
Q.1 (c) Define multiple encryption.
Answer:
Multiple encryption means encrypting data more than once using the same or different keys/algorithms (e.g., Triple DES) to increase security.
Q.1 (d) Define confidentiality and authentication.
Answer:
- Confidentiality: Only authorized users can access information.
- Authentication: Verification of a user’s or system’s identity.
Q.1 (e) What is the difference between Feistel and non-Feistel ciphers?
Answer:
- Feistel Cipher: Splits data into two halves and processes them alternately. Encryption and decryption processes are similar. Example: DES.
- Non-Feistel Cipher: Processes the entire block in one operation. Encryption and decryption require separate functions. Example: AES.
Q.1 (f) Explain traditional block cipher structure.
Answer:
Traditional block ciphers (like DES) use multiple rounds. Each round has operations like substitution, permutation, and mixing sub-keys. The plaintext block is split into two halves and processed repeatedly.
Q.1 (g) Find the multiplicative inverse of 23 in Z100.
Answer:
The multiplicative inverse of 23 (mod 100) is 87.
Q.1 (h) What is message authentication?
Answer:
Message authentication verifies two things:
- The message came from the claimed sender.
- The message was not modified in transit.
It is done using MACs, hashes, or digital signatures.
Q.1 (i) State Euler’s theorem with example.
Answer:
Euler’s theorem:
If a and n are coprime, then raising a to the power phi(n) leaves remainder 1 when divided by n.
Example: For n = 10, phi(10) = 4.
3^4 = 81, and 81 mod 10 = 1.
Q.1 (j) What are the properties a digital signature should have?
Answer:
- Authenticity – Identifies the signer.
- Integrity – Confirms message has not changed.
- Non-repudiation – The signer cannot deny sending it.