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Cryptography Unit1

Total questions: 25

Worksheet time: 7mins

Name
Class
Date
1.

What is the main goal of modern cryptography?

a)
To ensure that all data is publicly accessible.
b)
To eliminate all forms of data encryption.
c)
To ensure confidentiality, integrity, and authenticity of information.
d)
To create unbreakable codes for secret messages.
2.

Which encryption method uses a public and private key?

a)
Asymmetric encryption
b)
Symmetric encryption
c)
Base64 encoding
d)
Hashing
3.

Which algorithm is a popular asymmetric encryption method?

a)
DES
b)
RSA
c)
AES
d)
Blowfish
4.

RSA encryption relies on which mathematical problem?

a)
Discrete logarithm problem
b)
Elliptic curve problem
c)
Integer factorization problem
d)
Prime number generation problem
5.

What is the GCD of 48 and 18?

a)
6
b)
36
c)
24
d)
12
6.

What does Euler’s Theorem state?

a)
If n is a positive integer, then a^n ≡ 0 (mod n).
b)
If n is a positive integer and a is coprime to n, then a^φ(n) ≡ 1 (mod n).
c)
If a is any integer, then a^φ(n) ≡ n (mod n).
d)
If n is a prime number, then a^n ≡ a (mod n).
7.

What is the modular inverse of 3 modulo 7?

a)
6
b)
2
c)
5
d)
4
8.

What is the probability of drawing an Ace from a deck of 52 cards?

a)
2/13
b)
1/52
c)
1/26
d)
1/13
9.

What does the Caesar Cipher do?

a)
The Caesar Cipher replaces letters with numbers based on their position.
b)
The Caesar Cipher scrambles text randomly without any fixed pattern.
c)
The Caesar Cipher decrypts text by reversing the order of letters.
d)
The Caesar Cipher encrypts text by shifting letters a fixed number of places in the alphabet.
10.

How many keys are possible in a monoalphabetic cipher?

a)

26

b)

100

c)

26^2

d)

26!

11.

The Vigenère cipher is an example of:

a)
A monoalphabetic substitution cipher
b)
A block cipher
c)
A polyalphabetic substitution cipher
d)
A transposition cipher
12.

What classical cipher is easily broken using frequency analysis?

a)
Transposition cipher
b)
Playfair cipher
c)
Vigenère cipher
d)
Caesar cipher
13.

What is frequency analysis used for?

a)

Breaking substitution ciphers

b)

Compressing data

c)

Securing data

d)

Creating hash functions

14.

Why are polyalphabetic ciphers harder to break?

a)
Polyalphabetic ciphers are harder to break because they use multiple substitution alphabets, reducing the effectiveness of frequency analysis.
b)
They are based on a fixed key length, simplifying decryption.
c)
They rely on simple letter replacement, which is predictable.
d)
They use a single substitution alphabet, making them easier to analyze.
15.

According to Shannon, which property hides the relationship between ciphertext and key?

a)
Encryption
b)
Diffusion
c)
Confusion
d)
Decryption
16.

Perfect secrecy means:

a)
The ciphertext is longer than the plaintext.
b)
The plaintext can be derived from the ciphertext.
c)
The ciphertext is easily decipherable.
d)
The ciphertext reveals no information about the plaintext.
17.

What is the ciphertext for the plaintext “HELLO” using a Caesar cipher with key = 3?

a)

KHOOS

b)
KHOOR
c)

KGOOR

d)

JHOOS

18.

Find the value of 3^4 mod5.

a)
3
b)
2
c)
1
d)
4
19.

Decrypt the Caesar cipher text "WRUGRN" with key = 13.

a)
QWERTY
b)
ASDFGH
c)
JEHTEA
d)
ZXCVBN
20.

In RSA, let p = 3, q = 11. Find n and ϕ(n).

a)
n = 33, ϕ(n) = 20
b)
n = 36, ϕ(n) = 22
c)
n = 30, ϕ(n) = 18
d)
n = 33, ϕ(n) = 15
21.

What is the remainder when 7⁴ is divided by 10?

a)
1
b)
2
c)
8
d)
5
22.

What is the value of gcd⁡(270,192)?

a)
6
b)
24
c)
18
d)
12
23.

Solve for x: 5x≡1mod  7

a)
1
b)
2
c)
4
d)
3
24.

In a transposition cipher, what is the result of encrypting “HELLO” using columnar order 3-1-2?

a)
HELLO
b)
OLLEH
c)
LEOHL
d)

LHELO

25.

Which cipher uses a 5×5 matrix for encryption?

a)
Caesar cipher
b)
Playfair cipher
c)
Vigenère cipher
d)
RSA cipher

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