1. A tweak is used in XTS-AES mode to provide a different output for the same input PT and same key.
a) True
b) False
Explanation: The statement is true for XTS-AES mode of operation.
2. XTS-AES mode of operation is a better version of
a) OFB
b) CFB
c) CTR
d) ECB
Explanation: XTS-AES mode overcomes the principle security weakness of ECB, which is that two encryptions of the same CT yeild the same PT.
3. What is the size of the XTS-AES key?
a) 1024 bits
b) 64 bits
c) 512 bits
d) 128 bits
Explanation: The key size can be either 256 bits or 512 bits. There are 2 keys of the same size K1 and K2.
4. Which of the following represent the tweak?
a) j
b) i
c) alpha
d) alphaj
Explanation: ‘i’ represents the tweak value.
5. Which of the following is true for the tweak in XTS-AES mode?
a) they are non-negative integers
b) they are of size 128 bits
c) they are assigned consecutively
d) all of the mentioned
Explanation: All of the statements are true in relation to the tweak ‘i’ from the XTS-AES mode of operation.
6. Which of the following is the correct encryption statement representation for the XTS-AES mode?
a) E(K1,P) XOR T
b) E(K2,T) XOR P
c) E(K1,T XOR P) XOR P
d) E(K1,P XOR T) XOR T
Explanation: The correct encryption representation would be : C = E(K1,P XOR T) XOR T.
7. The last two blocks of the XTS-AES mode are –
a) padded as 10*
b) encrypted/ decrypted using ciphertext-stealing
c) padded as 10*1
d) padded and then swapped after encryption/ decryption
Explanation: The correct term used to encrypt/ decrypt the last 2 blocks is ‘cipher-text stealing’ where C(m) and C(m-1) are interchanged with each other.
8. PRNG stands for
a) Personal Random Number Generation
b) Pseudo Random Number Generation
c) Primitive Number Generators
d) Private Number Generators
Explanation: PRNG stands for Pseudo Random Number Generation.
9. TRNG stands for
a) True Random Number Generation
b) Trust Random Number Generation
c) Text Ring Number Generators
d) None of the mentioned
Explanation: TRNG stands for True Random Number Generation.
10. A rule to check for a large number N being a prime number
a) by dividing N by every even interger less than N/2
b) by dividing N by every odd interger less than root(N)
c) by dividing N by every even interger less than root(N)
d) by dividing N by every interger less than N/2
Explanation: A rule for checking if a number N is a prime is by dividing N by every odd interger less than root(N).