4- Consider a block cipher whose block length is 𝑛. 𝑁 = 2^n is number of possibilities. Imagine wehave 𝑡 plain text-cipher text pairs 𝑃i, 𝐶i = 𝐸k(𝑃i) , where the key 𝐾 selects one of the 𝑁! Possiblemappings. Now, imagine you want to brute force this encryption algorithm for the key. In each try,you generate the test key 𝐾′ and check whether 𝐶i = 𝐸(𝐾'ᇱ, 𝑃i); i=1,…,t. If 𝐾'ᇱ maps 𝑃i to its proper𝐶i, we have an evidence that 𝐾'ᇱ = 𝐾. However, it could be the case that 𝐸k(. ) a

Consider a new block cipher, DES2, that consists only of two rounds of the DES block cipher. DES2 has the same block and key size as DES. For this question you should consider the DES F function as a black box that takes two inputs, a 32 -bit data segment and a 48 -bit round key, and that produces a 32-bit output. Suppose you have a large number of plaintext-ciphertext pairs for DES2 under a single, unknown key. Give an algorithm for recovering the 48 -bit round key for round 1 and the 48 -bit r