Question 1

Distinguish between the following:

i) A block cipher and a stream cipher
ii) Diffusion and Confusion

i) A block cipher encrypts data in fixed-size blocks, while a stream cipher encrypts data bit by bit or byte by byte.
ii)

Question 2

What kind of attack on double DES makes it useless? Explain briefly.
	
The attack that makes Double DES (2DES) ineffective is called the Meet-in-the-Middle attack. 
Although 2DES was designed to increase security by using two keys (encrypting the plaintext twice with different keys), this attack significantly reduces its effectiveness. 
Instead of trying all possible combinations of two 56-bit keys (which would take 2¹¹² attempts), the Meet-in-the-Middle attack allows an attacker to match encrypted and decrypted values in the middle, reducing the effort to about 2⁵⁷ operations. 
This is only slightly more secure than regular DES, which requires 2⁵⁶ operations, making 2DES practically useless as a secure encryption method.

Question 1

Question 2

Question 1

Question 2

Question 3

Question 4

Question 5