IIl. Block Ciphers Exercise #7 Ben Bitdiddle has invented a Feistel cipher and hired you to check if it is secure. His cipher opreates on 64-bit block and consists of 4 rounds. For each round Li = Ri-1 Fe(m) = kBrn The same 32-bit key, k is used for each round. You are given the plaintext-ciphertext pair: Plaintext: 0001100100001101011101001100011101101011010100010011101001100010 ciphertext: 0111001001011100010011101010010101101011010100010011101001100010 Ben is stubbornly convinced of his genius and the invincibility of his cipher, and is not disturbed by the odd similarily between the second half of the ciphertext and the second half of the plaintext. Convince Ben the cipher is insecure by determining the key