# Vigenère Cipher Multiple Choice Questions and Answers (MCQs)

This set of Data Structures & Algorithms Multiple Choice Questions & Answers (MCQs) focuses on “Vigenère Cipher”.

1. What is the meaning of cipher in cryptography?
a) an algorithm that performs encryption
b) an algorithm that generates a secret code
c) an algorithm that performs encryption or decryption
d) a secret code

Explanation: Cipher is an algorithm for performing encryption or decryption. In cryptography, a set of defined steps are followed to generate ciphers. These are necessary to prevent data breach.

2. Vigenere cipher is an example of ______________
a) mono-alphabetic cipher
b) poly-alphabetic cipher
c) transposition cipher

Explanation: Vigenere cipher is a substitution cipher. It falls under the category of poly alphabetic cipher as it uses multiple substitution at different positions in order to cipher the plain text.

3. Encryption in Vigenere cipher is done using _________
a) vigenere formula
b) vigenere cycle
c) vigenere square

Explanation: Encryption of plain text using vigenre cipher is done by making use of vigenere table. It is also known as vigenere square.

4. Which of the following correctly defines poly alphabetic cipher?
a) a substitution based cipher which uses multiple substitution at different positions
b) a substitution based cipher which uses fixed substitution over entire message
c) a transposition based cipher which uses multiple substitution at different positions
d) a transposition based cipher which uses fixed substitution over entire message

Explanation: Poly alphabetic cipher is a type of substitution cipher. It uses multiple substitution at different positions in order to cipher the plain text.

5. Which of the following is not a type of poly alphabetic cipher?
a) Rotor cipher
b) Hill cipher
d) Multiplicative cipher

Explanation: In poly alphabetic cipher each symbol of plain text is replaced by a different cipher text regardless of its occurrence. Out of the given options only multiplicative cipher is not a poly alphabetic cipher.
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6. Vigenere table consists of _________
a) 26 rows and 26 columns
b) 26 rows and 1 column
c) 1 row and 26 columns
d) 27 rows and 27 columns

Explanation: Encryption of plain text using vigenre cipher is done by making use of vigenere table. It consists of 26 rows and 26 columns which have alphabets written 26 times. These are shifted towards left after each row.

7. Vigenere cipher is harder to decipher than keyword cipher.
a) true
b) false

Explanation: Keyword cipher is less secure than vigenere cipher. It is due to the fact that keyword cipher is mono alphabetic and thus can be cracked using frequency analysis. But vigenere cipher being a poly alphabetic cipher cannot be deciphered using this method.

8. What will be the plain text corresponding to cipher text “PROTO” if vigenere cipher is used with keyword as “HELLO”?
a) SANFOUNDRY
b) WORLD
c) INDIA
d) AMERICA

Explanation: Vigenere cipher is a type of poly alphabetic substitution which uses vigenere table for making substitutions in the plain text. Using the table we find the plain text to be “INDIA”.

9. Which cipher is represented by the following function?

```public class Cipher
{
public static String encrypt(String text, final String key)
{
String res = "";
text = text.toUpperCase();
for (int i = 0, j = 0; i < text.length(); i++)
{
char c = text.charAt(i);
if (c < 'A' || c > 'Z')
continue;
res += (char) ((c + key.charAt(j) - 2 * 'A') % 26 + 'A');
j = ++j % key.length();
}
return res;
}```

a) vigenere cipher
b) hill cipher
c) keyword cipher
d) rotor cipher

Explanation: The given function represents the function of hill cipher. It is a type of poly alphabetic substitution which makes use of the vigenere table for making substitutions in the plain text.

10. In which of the following cipher the plain text and the ciphered text does not have a same number of letters?
a) affine cipher
b) vigenere cipher
c) columnar cipher

Explanation: In transposition cipher and mono alphabetic cipher the number of letters remain same in ciphered and deciphered text. But in poly alphabetic cipher the number of letters are different. So here as vigenere cipher is the only poly alphabetic cipher so it will be the answer.

11. What will be the ciphered text if the string “SANFOUNDRY” is given as input to the code of vigenere cipher with keyword as “HELLO”?
a) UEWIIDKLL
b) ZEYQCOCM
c) ZEYQCBROCM
d) ZEYQCBROCMJDH

Explanation: Vigenere cipher is a type of poly alphabetic substitution which uses vigenere table for making substitutions in the plain text. Using the table we find the solution to be ZEYQCBROCM.

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