53) Ceasar Cipher is one of the earliest classical substitution ciphers. It involves replacing each letter in the plaintext by a shifted 1) letter in the alphabet used.

Mathematically it can be expressed as follows: c = E(p) = (p + k) mod (26) p = D(c) = (c k) mod (26) where p and c refer to the plaintext and ciphertext, respectively; E(p) and D(C) are the encryption and decryption functions, respectively; and k is the secret key. a) Show the encryption and decryption processes of the plaintext Attack at dawn using a key value of 4; b) Explain how a brute force attack can break this simple cryptosystem; c) Use a brute force attack to decrypt (decipher) the following message TEBKFKQEBZLROPBLCERJXKBSBKQP.

What is the original plaintext and the encryption key used?