Question#1
What is the main characteristic of a polyalphabetic cipher like the Vigenère cipher?
a) It uses numeric keys for simple XOR operations.
b) It shifts each character by a fixed number of positions.
c) It rearranges the position of plaintext characters only.
d) It uses multiple substitution alphabets for encryption. ✅ - Answer

Question#2
How is the Vigenère table, also known as Tabula Recta, structured?
a) It is a 26 x 1 matrix of numeric values.
b) It is a single row of shifted alphabets.
c) It is a table of random numbers assigned to each letter.
d) It is a 26 x 26 matrix representing shifted alphabets. ✅ - Answer

Question#3
Which of the following describes how the encryption in Vigenère cipher is performed using the Vigenère table?
a) By reversing the letters of the plaintext.
b) By finding the intersection of the column of the plaintext letter and the row of the key letter. ✅ - Answer
c) By summing numeric values of plaintext and key.
d) By shifting each letter by a single fixed number.

Question#4
What happens if the decryption formula in the Vigenère cipher yields a negative value?
a) Subtract 26 from the negative value.
b) Take the absolute value directly.
c) Ignore the value and move to the next.
d) Add 26 to the negative value to get a valid letter position. ✅ - Answer

Question#5
In the one-time pad technique, what must be true about the key?
a) The key must be a single letter repeated.
b) The key must be twice as long as the plaintext.
c) The key must be the same length as the plaintext. ✅ - Answer
d) The key can be any arbitrary length.

Question#6
Which cryptographic attribute does the one-time pad (Vernam cipher) guarantee if used properly?
a) It is unbreakable and completely secure. ✅ - Answer
b) It requires public-key cryptography.
c) It only secures numeric data well.
d) It is breakable with modern computers.

Question#7
What mathematical operation is fundamental to both the encryption and decryption processes in the Hill cipher?
a) Matrix multiplication modulo 26. ✅ - Answer
b) Bitwise XOR of plaintext and key.
c) Alphabetical sorting of plaintext letters.
d) Simple addition modulo 10.

Question#8
Which cipher requires the key to be formed into a square matrix for encryption?
a) Vigenère cipher
b) One-time pad cipher
c) Hill cipher ✅ - Answer
d) Rail Fence cipher

Question#9
In the decryption step of the Hill cipher, what must be calculated before multiplying by the ciphertext vector?
a) The product of all key matrix entries.
b) The permutation of the key matrix.
c) The sum of the ciphertext vector.
d) The inverse of the key matrix modulo 26. ✅ - Answer

Question#10
Which type of encryption technique is the rail fence cipher an example of?
a) Transposition cipher ✅ - Answer
b) Symmetric block cipher
c) Asymmetric encryption cipher
d) Polyalphabetic substitution cipher

Question#11
How does the rail fence cipher alter the plaintext message?
a) It XORs every character with a key value.
b) It rearranges the positions of the plaintext characters. ✅ - Answer
c) It substitutes each character with a numeric value.
d) It replaces every letter with its complement in the alphabet.

Question#12
In the context of digital signatures, which cryptographic key is used to create the signature?
a) The recipient's private key
b) The certificate authority's public key
c) The sender's private key ✅ - Answer
d) The sender's public key

Question#13
Why is it important that a digital signature’s certificate is not expired?
a) To allow unlimited message signing.
b) To ensure that the signature can be trusted and verified. ✅ - Answer
c) To increase data transmission speed.
d) To avoid decrypting the message digest twice.

Question#14
What does nonrepudiation mean in the context of digital signatures?
a) The sender cannot deny association with the signed content. ✅ - Answer
b) Only the message can be decrypted securely.
c) The signature expires after a specific time.
d) Only the content’s integrity is maintained.

Question#15
Which statement best describes message integrity in digital signatures?
a) The message was encrypted before transmission.
b) The message content was not changed after it was signed. ✅ - Answer
c) No one read the message en route.
d) Only the public key was used during transmission.

Question#16
During Rail Fence cipher encryption, how is the plaintext written?
a) Randomly distributed in columns.
b) From right to left in alternate lines.
c) Downwards and diagonally on successive rails of an imaginary fence. ✅ - Answer
d) Straight left to right multiple times.

Question#17
What main advantage does the Hill cipher offer over other classical ciphers?
a) It appends random characters for extra security.
b) It can encrypt blocks of letters of various sizes using linear algebra. ✅ - Answer
c) It uses no mathematical operations at all.
d) It always uses a public key infrastructure.

Question#18
In the Vigenère cipher, how do you generate the key if the plaintext is longer than the keyword?
a) Use the previous ciphertext letter as the next key letter.
b) Reverse the keyword for the remaining letters.
c) Only use the keyword once, then stop.
d) Repeat the keyword in a circular manner until it matches the length of the plaintext. ✅ - Answer

Question#19
What is the function of a certificate authority (CA) in digital signature verification?
a) It encrypts all signed content directly.
b) It manages the symmetric keys for all users.
c) It creates the message digest used in signatures.
d) It signs certificates and allows users to verify signatures using its public key. ✅ - Answer

Question#20
Which aspect of the one-time pad cipher helps make it theoretically unbreakable?
a) It rearranges characters in a fixed transposition.
b) It uses public-key cryptography for key exchange.
c) The key is truly random and as long as the plaintext. ✅ - Answer
d) The key is much shorter than plaintext.