## Problem Set

Here is a problem set for students.

Time: 30 mins

Max score: 100

1) Input: I know this
Output: 0c081a92a4b4221cb2e059cf46c2c7e5
What is this process called?
a) Substitution
b) Decryption
c) Hashing
d) Encryption

2) Input: “You can be a cryptographer too”.
Output: “Aqw ecp dg b etarvqitcrjgt vqq”.
This is a simple substitution cipher. What is the key?
a) 1
b) 2
c) 3
d) 4

3) The following problem is based on one time pad.
Key: RQBOPS
Message: ATTACK
What is the encrypted message?
a) XRTTHG
b) RQBOPS
c) RJUORC
d) ATTACK

4) Now it’s time for you to be the codebreaker! Using the Polybius square technique, decrypt the following message – 014343325
a) Done
b) Good
c) Pray
d) Nope

5) If a message is 1 2 3 4 5 6 5 4 3 2 1, and key = 423, what is the encrypted message?
a) 7 6 5 8 9 3 3 5 6 2 1
b) 1 2 3 4 5 6 7 8 9 0 1
c) 4 2 3 4 2 3 4 2 3 4 2
d) 5 4 6 6 9 8 8 6 7 4 4
(hint: repeat 423 as many times as required to generate entire key sequence)

6) Decrypt the following message by picking the appropriate technique: Uif fofnz jt bqqsbdijoh.
a) The times are changing
b) The enemy is approaching
c) This batch is destroyed
d) The ghost is approaching

7) What type of encryption is the following?
Input: Hello
Output: khoor
b) Polybius square technique
c) Substitution
d) Public key encryption

8) For a message, Caesar shift with key 3 is applied. What is the original message if the encrypted message is: DEFGHIJKLMNOPQRSTUVWXYZABC
a) TUVWXYZABCDEFGHIJKLMNOPQRS
b) ABCDEFGHIJKLMNOPQRSTUVWXYZ
c) CDEFGHIJKLMNOPQRSTUVWXYZAB
d) DEFGHIJKLMNOPQRSTUVWXYZABC

9) Alice added two numbers and hashed her solution and sent it to Bob. Bob added the same 2 numbers, hashed his solution and compared his hash with Alice’s hashed solution. When can he say his solution is the same as hers?
a) When both the hashes are EXACTLY the same
b) If the hashes are of same length
c) If both the answers are fed to the same hashing generator
d) If after feeding both the answers to the same hashing generator, the hashes are exactly the same.

10) Which cipher is unbreakable?
a) Caesar cipher
c) Vignere cipher
d) Polybius square

Solution set:
1) Ans: c
2) Ans: b
3) Ans: c
4) Ans: a
5) Ans: d
6) Ans: b
7) Ans: c
8) Ans: b
9) Ans: d