Data Structures & Algorithms Multiple Choice Questions on “Hill Cipher”.
1. Hill cipher requires prerequisite knowledge of?
a) integration
b) differentiation
c) matrix algebra
d) differential equation
Answer: c
Clarification: Hill cipher uses matrix multiplication in order to encrypt the given plain text. So it requires prerequisite knowledge of matrix algebra.
2. Hill cipher is an example of ____________
a) mono-alphabetic cipher
b) substitution cipher
c) transposition cipher
d) additive cipher
Answer: b
Clarification: Hill cipher is a substitution cipher. It falls under the category of poly alphabetic cipher as it uses multiple substitutions at different positions in order to cipher the plain text.
3. Encryption in hill cipher is done using ______________ Answer: a 4. What is poly graphic substitution cipher? Answer: c 5. Which of the following was the first poly graphic cipher to be able to operate on more than 3 letters at once? Answer:b 6. Which of the following is hardest to break using frequency analysis? Answer: b 7. Hill cipher is harder to crack than playfair cipher. Answer: b 8. What will be the plain text corresponding to cipher text “YGQ“ if hill cipher is used with keyword as “GYBNQKURP”? Answer: a 9. What will be the size of a key matrix if the plain text is “SECRET”? 10. A key matrix used for encryption in hill cipher must be? 11. What will be the ciphered text if the plain text “SAN” is encrypted using hill cipher with keyword as “GYBNQKURP”? and Answers.
a) matrix multiplication
b) a 5×5 table
c) vigenere table
d) matrix inversion
Clarification: Encryption of plain text in playfair cipher is done using matrix multiplication. Then modulo 26 of the resulting matrix is taken so as to get the ciphered text.
a) a substitution based cipher which uses multiple substitutions at different positions
b) a substitution based cipher which uses fixed substitution over entire plain text
c) a substitution based cipher in which substitution is performed over a block of letters
d) a transposition based cipher which uses fixed substitution over entire plain text
Clarification: Poly graphic cipher is a type of substitution cipher in which substitution is performed over a block of letters. Hill cipher is an example of poly graphic cipher.
a) autokey cipher
b) hill cipher
c) one time pad cipher
d) playfair cipher
Clarification: Poly graphic cipher is a type of substitution cipher in which substitution is performed over a block of letters. Hill cipher was the first poly graphic cipher to be able to operate on more than 3 letters at once.
a) Vigenere cipher
b) Hill cipher
c) Caesar cipher
d) Affine cipher
View Answer
Clarification: Out of the given options hill cipher is the hardest cipher to break using frequency analysis. Although it is quite vulnerable to other forms of attack.
a) True
b) False
Clarification: Both hill cipher and playfair cipher are less vulnerable to frequency analysis. But hill cipher is quite vulnerable to other forms of attack and thus less secure than playfair cipher.
a) SECRET
b) WORLD
c) DOLLAR
d) HELLO
View Answer
Clarification: To decrypt the message we follow the reverse procedure. We first find the inverse of the keyword matrix then multiply it with cipher matrix.
a) 1×6
b) 5×1
c) 6×1
d) 6×6
Answer: d
Clarification: Hill cipher uses a n x n matrix in order to cipher the plain text. In this case n=6 so a 6×6 matrix will be used.
a) invertible matrix
b) non invertible matrix
c) square matrix
d) rectangular matrix
Answer: a
Clarification: A key matrix used for encryption in hill cipher must be invertible matrix. Otherwise it will be impossible to decipher the message.
a) RAJ
b) JAR
c) ARJ
d) AJR
Answer: a
Clarification: We first convert the keyword and plain text into their corresponding matrix respectively. Then we multiply those matrix and take modulo 26 of the resulting matrix to get the ciphered text.