Not a programming Q

Problem 2: Shift Cipher (a). Assume a message m is encrypted using the Shift cipher and the resulting ciphertext is as follows: TEBKFKQEBZLROPBLCERJXKBSBKQP What would be the values of m and key k in this case? Assume that encryption and decryption in the shift cipher are defined as Ci = (mi - k) mod 26 and m; = (ci + k) mod 26, respectively. Here mi and c; denote the ith character in message m and ciphertext c, respectively. Please justify your answer. (Hint: you need to do an exhaustive search or brute force attack over 26 possible keys.) (50 points)