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WorksheetsUNIT 2 MCQ QUESTIONS - Cryptography and Network Security
Total questions: 75
Worksheet time: 38mins
Assume RSA public key is (e = 3, n = 33). What is the ciphertext for plaintext message M = 4?
64
31
28
16
In RSA algorithm, if p = 11 and q = 13, and e = 7, what is the value of the public modulus n and Euler’s totient φ(n)?
n = 143, φ(n) = 120
n = 24, φ(n) = 132
n = 143, φ(n) = 132
n = 24, φ(n) = 120
Which of the following cryptographic techniques is a Symmetric cryptography?
RSA
Diffie-Hellman
DES
ECC
In the context of block cipher modes of operation, which mode offers both confidentiality and message integrity?
ECB
CBC
CTR
GCM
What is the block size of DES?
32 bits
64 bits
128 bits
256 bits
What type of cipher is DES?
Stream cipher
Asymmetric cipher
Block cipher
One-time pad
A 64-bit block of plaintext is encrypted using 3-DES with three different keys. How many total DES operations are performed during encryption?
1
2
3
6
DES is based on which structure?
Feistel network
Substitution-permutation
LFSR
RSA
Which of the following statements about Blowfish is TRUE?
It is a block cipher with a 64-bit block size and a key length up to 448 bits
It is a stream cipher used in TLS
It is a public key encryption algorithm
It uses a 512-bit fixed key
RC5 is a symmetric key cipher with which of the following characteristics?
Fixed 128-bit block size
Variable word size, rounds, and key size
Based on elliptic curves
Asymmetric encryption only
In RSA, if the ciphertext is c = 10, the decryption key d = 7, and the modulus n = 33, what is the plaintext m?
10
1
13
4
What does ECB stand for in DES modes of operation?
Electronic Code Base
Electronic Code Book
Encrypted Cipher Block
Encrypted Code Buffer
In DES, how many rounds of permutation and substitution are performed on the plaintext?
10
16
32
8
What does S-box stand for in DES?
Secret box
Substitution box
Secure box
Shared box
Quantum cryptography primarily relies on which principle?
RSA key exchange
Shor’s algorithm
Heisenberg’s uncertainty principle
Fermat’s Little Theorem
What is the purpose of the Feistel structure in DES?
To increase processing time
To make encryption faster
To allow same algorithm for encryption and decryption
To change key size
Which property of a stream cipher differentiates it from a block cipher?
Stream ciphers encrypt data in fixed-size blocks.
Stream ciphers use public key encryption.
Stream ciphers encrypt data one bit or byte at a time.
Stream ciphers use substitution and transposition together.
Which of the following algorithms is not a symmetric key algorithm?
RC5
Blowfish
RSA
3-DES
In the RSA algorithm, the modulus n is calculated as:
n=p+q
n=p×q
n=(p−1)(q−1)
n=pq
How many bits are there in the right and left halves during each DES round?
32 bits each
64 bits each
28 bits each
56 bits each
RSA is based on which type of cryptography?
Symmetric key cryptography
Hashing algorithm
Asymmetric key cryptography
Stream cipher
In RSA, the public key consists of:
(e, d)
(n, d)
(e, n)
(p, q)
In 3-DES encryption, the effective number of keys used in the encryption process is:
1
2 or 3 depending on implementation
4
6
Given a plaintext “10101010” and a key “11001100”, what is the cipher text in a simple XOR stream cipher?
01100110
10101010
11111111
01010101
What is the formula for RSA encryption?
C = M × e mod n
C=Memodn
C = eMmodn
C = M + e + n
What is the first step in RSA key generation?
Find public exponent
Select two large prime numbers
Encrypt the message
Calculate modulus
In RSA, n is calculated as:
p + q
p – q
p × q
p ÷ q
Which of the following is a characteristic of the Blowfish algorithm?
Uses fixed 128-bit key size
Is a symmetric key block cipher with variable key length
Is a public key cryptosystem
Operates only on 256-bit blocks
The main purpose of key exchange algorithms is to:
Encrypt messages
Exchange secure keys over insecure channels
Authenticate users
Hash data
Which of the following is NOT a block cipher mode of operation?
CBC (Cipher Block Chaining)
RSA (Rivest–Shamir–Adleman)
ECB (Electronic Codebook)
OFB (Output Feedback)
The Diffie-Hellman algorithm is primarily used for:
Message authentication
Key exchange
Digital signatures
Data compression
Which of the following best describes Quantum Cryptography?
Uses quantum computers to break classical ciphers
Uses principles of quantum mechanics for secure key distribution
Is a new symmetric key cipher standard
Encrypts messages using quantum bits only
Which of the following is a key advantage of 3-DES over DES?
Faster encryption speed
Uses longer keys for better security
Works only on larger blocks
Uses asymmetric keys
Elliptic Curve Diffie-Hellman (ECDH) is a variant that uses:
Quantum cryptography
Elliptic curve mathematics
LFSR
S-boxes
Which cryptographic technique uses two different keys, one for encryption and one for decryption?
Symmetric key cryptography
Hashing
Asymmetric key cryptography
Stream cipher
In block cipher modes, which one does NOT require padding?
ECB
CBC
CTR (Counter)
OFB
How many bits are there in each DES subkey used in a round?
56 bits
48 bits
64 bits
32 bits
RSA uses how many keys?
1
2
3
4
In RSA, what is the value of n if p = 3 and q = 11?
14
33
21
30
If p = 3 and q = 11, what is φ(n)?
33
30
28
20
In RC5, which of the following parameters can be varied to increase security and flexibility?
Block size
Number of rounds
Key length
All of the above
What operation is primarily used in the DES Feistel structure?
Multiplication
XOR
AND
Division
What does ECC stand for in cryptography?
Encryption Control Code
Elliptic Curve Cryptography
Electronic Code Communication
Elliptic Compression Cipher
What does QKD stand for?
Quantum Key Decoder
Quantum Key Distribution
Quick Key Distribution
Quantum Kernel Deployment
If Blowfish uses 16 rounds and a 64-bit block size, what is the expected output size of the ciphertext for a 64-bit input?
16 bits
32 bits
64 bits
128 bits
In RSA, for p=17, q=11 and e=7 what is the value of φ(n)?
187
160
120
140
Which quantum property is used to detect eavesdropping in quantum cryptography?
Holography
Indistinguishability
Heisenberg’s Uncertainty Principle
Wave interference
For RSA, if p = 11 and q = 13, what is the value of φ(n)?
132
120
112
122
Which particles are commonly used in quantum key distribution?
Electrons
Photons
Protons
Neutrons
How many possible keys are there for a DES cipher?
24
256
2128
252
If Alice and Bob use RSA for secure communication and Bob's public key is (e = 7, n = 55), what is the ciphertext of the message M = 9?
9
14
4
19
You are designing a secure system. Which combination provides the best balance of speed, security, and scalability for encrypting bulk data on embedded devices?
RSA with large key size
ECC with 512-bit key
RC5 with 32-bit blocks
AES in CTR mode
Given two prime numbers, p = 11 and q = 13, and public exponent e = 7, what is the value of φ(n) in RSA?
143
132
120
60
In RSA, if the ciphertext C = 36, the private key d = 3, and n = 55, what is the original message M?
56
21
16
9
Quantum cryptography is currently best suited for:
Global internet encryption
Long-range satellite data
Secure communication over optical fiber
File compression
A symmetric cipher encrypts 64-bit blocks. The plaintext block is 0x1234567890ABCDEF, and the key schedule and operation result in ciphertext 0xA1B2C3D4E5F60718. What encryption type is this most likely to be?
Stream Cipher
RSA
DES
ECC
Which of the following is not a mode of operation in DES?
ECB
CBC
CFB
DFS
Which of the following correctly expresses the ciphertext generation in RSA encryption?
C = M * e mod n
C = M + e mod n
C=Memodn
C = Mmoden
In which DES mode is the plaintext divided into blocks and each block is encrypted separately?
CBC
ECB
CFB
OFB
If the plaintext message M = 7, public key e = 5, and modulus n = 33, what is the ciphertext C using RSA encryption?
7
14
31
17
In the RSA algorithm, p = 3 and q = 11. What is the modulus n and the Euler’s totient function φ(n)?
n = 14, φ(n) = 30
n = 33, φ(n) = 20
n = 33, φ(n) = 28
n = 14, φ(n) = 10
In the Diffie-Hellman key exchange, if g = 2, p = 11, and Alice chooses a private key a = 5, what is her public key?
8
9
6
1
Which mode of DES uses an Initialization Vector (IV) to encrypt the first block?
ECB
CBC
RSA
Hashing
In RSA, the public key is composed of:
(e, n)
(d, n)
(p, q)
(e, d)
In RSA, the private key is:
Known to everyone
(e, n)
(d, n)
(p, q)
DES encrypts 64-bit blocks using how many rounds of permutation and substitution?
8
12
16
24
A 3DES system applies DES encryption three times. If the same key is used for all three stages, what is the security level compared to regular DES?
Weaker
Same as DES
Slightly better
Stronger than DES
Which parameter is crucial for the security of the Diffie-Hellman key exchange?
Public Key
Private Key
Prime Number
Shared Secret
Which of the following encryption techniques uses mathematical problems involving elliptic curves over finite fields?
RSA
ECC
3DES
RC5
In RSA, if p = 7 and q = 13, what is the value of φ(n)?
72
90
78
84
Which of the following is a block cipher?
RC4
DES
Vigenère
Caesar
In RSA, if the ciphertext C = 20, e = 3, and n = 33, what is the plaintext M after decryption using d = 7?
2
26
8
11
Which block cipher mode introduces dependency between cipher blocks for better security?
ECB
CBC
OFB
CTR
If the Blowfish algorithm uses 16 rounds, what does each round involve?
Only permutation
Only substitution
Substitution and permutation
Key generation
Which of the following is a stream cipher?
AES
Blowfish
RC4
3DES
