Question#1
The Playfair cipher is classified as a _____ substitution cipher.
a) digraphic ✅ - Answer
b) monoalphabetic
c) homophonic
d) polyalphabetic

Question#2
In symmetric encryption, the secret key may be generated by a _____ .
a) secure random number generator ✅ - Answer
b) public certificate authority
c) hardware security module only
d) elliptic curve algorithm

Question#3
The primary security risk of symmetric encryption is the _____ .
a) requirement for secure key exchange ✅ - Answer
b) need for large block sizes
c) public nature of the key
d) slowness of encryption process

Question#4
Caesar cipher encryption uses a fixed key of _____ for shifting letters.
a) 3 ✅ - Answer
b) 7
c) 1
d) 5

Question#5
Block ciphers encrypt data in _____ of fixed length simultaneously.
a) blocks ✅ - Answer
b) pairs
c) streams
d) chained segments

Question#6
The formula for decrypting a Caesar cipher is pt = d(k, ct) = (ct - k) _____ .
a) mod 26 ✅ - Answer
b) plus 26
c) divided by 26
d) minus 26

Question#7
In a shift cipher, the key value can range from _____ .
a) 0 to 25 ✅ - Answer
b) 1 to 25
c) 1 to 26
d) 0 to 26

Question#8
In asymmetric encryption, the public key is used primarily for _____ .
a) encrypting data ✅ - Answer
b) generating session IDs
c) creating digital signatures
d) decrypting data

Question#9
Diffie-Hellman is best described as an example of _____ encryption.
a) asymmetric ✅ - Answer
b) symmetric
c) stream cipher
d) polygraphic

Question#10
If a negative number occurs during decryption in Caesar cipher, _____ is added.
a) 26 ✅ - Answer
b) 13
c) the key
d) 1

Question#11
AES, DES, IDEA, Blowfish, RC5 and RC6 are all examples of _____ .
a) block ciphers ✅ - Answer
b) stream ciphers
c) asymmetric algorithms
d) digest methods

Question#12
Non-repudiation in asymmetric encryption means _____ .
a) sender cannot deny sending a message ✅ - Answer
b) key cannot be reused
c) cipher text is identical to plaintext
d) receiver authenticates all messages

Question#13
The Playfair matrix uses a keyword and treats 'I' and 'J' as _____ .
a) one letter ✅ - Answer
b) separate letters
c) swappable
d) filler letters

Question#14
A stream cipher encrypts data _____ .
a) as it streams ✅ - Answer
b) in fixed-size chunks
c) once the block is complete
d) after the session ends

Question#15
Digital signatures confirm the _____ of documents using asymmetric encryption.
a) legitimacy ✅ - Answer
b) complexity
c) interoperability
d) efficiency

Question#16
The encryption formula for shift ciphers is ct = e(k, pt) = (pt + k) _____ .
a) mod 26 ✅ - Answer
b) divided by 26
c) plus 26
d) times key

Question#17
In Playfair cipher, if a pair has same row, each letter is replaced by _____ .
a) the letter to its right ✅ - Answer
b) the letter above
c) the letter to its left
d) the letter beneath

Question#18
Asymmetric encryption removes the need for a protected channel for _____ .
a) key distribution ✅ - Answer
b) bulk data transfer
c) compressing cipher text
d) streamlining block size

Question#19
The Hill cipher is classified under _____ based on the text.
a) substitution techniques ✅ - Answer
b) transposition ciphers
c) asymmetric algorithms
d) block cryptosystems

Question#20
When decrypting in Playfair, if two letters are same column, use the letter _____ .
a) above each in same column ✅ - Answer
b) below each in same column
c) to the right in same row
d) to the left in same row