Question

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

I have been asked this question during an online interview.

My question is from DES Modes of Operation topic in section Advanced Encryption Algorithm and Block Cipher Operation of Cryptograph & Network Security

Answer 1

Right answer is (b) encrypted/ decrypted using ciphertext-stealing

For explanation I would say: 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.