Generic selectors
Exact matches only
Search in title
Search in content
Search in posts
Search in pages
Filter by Categories
nmims post
Objective Type Set
Online MCQ Assignment
Question Solution
Solved Question
Uncategorized

1. “Rabin Cryptosystem is a variant of the Elgamal Cryptosystem”
a) True
b) False

View Answer

Answer: b [Reason:] Rabin Cryptosystem is a variant of the RSA Cryptosystem.

2. Using Rabin cryptosystem with p=23 and q=7
Encrypt P=24 to find ciphertext. The Cipher text is
a) 42
b) 93
c) 74
d) 12

View Answer

Answer: b [Reason:] Calculate n = p × q = 161 Plaintext P = 24 Ciphertext = C ≡ P2 (mod n) = 242 mod 161 = 93 mod 161 Ciphertext transmitted = 93.

3. Which Cryptographic system uses C1 = (e1r) mod p and C1 = (e2r x P) mod p at the encryption side?
a) Elgamal
b) RSA
c) Rabin
d) Whirlpool

View Answer

Answer: a [Reason:] The Elgamal cryptographic system uses the above formulae to compute the CT.

4. Sender chooses p = 107, e1 = 2, d = 67, and the random integer is r=45. Find the plaintext to be transmitted if the ciphertext is (28,9).
a) 45
b) 76
c) 66
d) 13

View Answer

Answer: c [Reason:] P = [C2 (C1d)-1] mod p = 66.

5. Sender chooses p = 107, e1 = 2, d = 67, and the random integer is r=45. Find the plaintext to be transmitted if the ciphertext is (28,9).
a) 45
b) 76
c) 66
d) 13

View Answer

Answer: c [Reason:] P = [C2 (C1d)-1] mod p = 66.

6. In Elgamal cryptosystem, given the prime p=31.
Choose e1= first primitive root of p and d=10, calculate e2.
a) 24
b) 36
c) 25
d) 62

View Answer

Answer: c [Reason:] We choose e1=3 (a primitive root of p = 31) and d=10. Then we have e2 = 310 mod 31 = 25.

7. In Elgamal cryptosystem, given the prime p=31.
Encrypt the message “HELLO”; use 00 to 25 for encoding. The value of C2 for character ‘L’ is
a) 12
b) 07
c) 20
d) 27

View Answer

Answer: d [Reason:]The Common factor for the calculation of C2 is e7 mod 31 = 257 mod 31 = 25. P = “L” = 11; C1 = 37 mod 31 = 17; C2 = 11 x 25 mod 31 = 27; C = (17,27).

8. In Elgamal cryptosystem, given the prime p=31.
Encrypt the message “HELLO”; use 00 to 25 for encoding. The value of C2 for character ‘O’ is
a) 09
b) 07
c) 23
d) 27

View Answer

Answer: a [Reason:]The Common factor for the calculation of C2 is e7 mod 31 = 257 mod 31 = 25. P = “O” = 14; C1 = 37 mod 31 = 17; C2 = 14 x 25 mod 31 = 09; C = (17,09).

9. In Elgamal cryptosystem, given the prime p=31.
What is the respective plaintext character for C = (27, 20)?
a) H
b) L
c) O
d) M

View Answer

Answer: a [Reason:] The Common factor for the calculation of C2 is e7 mod 31 = 257 mod 31 = 25. C = 17, 20); P = 20 X (1710)-1 mod 31 = 07; “07” = “H”.

.woocommerce-message { background-color: #98C391 !important; }