Problem 5:. (a) The ciphertext ONXM was encrypted by a Hill cipher with a 2 x 2 matrix. The plaintext is null. Find the encryption matrix. (b) Suppose the ciphertext is PNXM and the plaintext is still null. Find the encryption matrix. Note that the first column of the matrix is changed. What does it mean? Is it a good or a bad property of a cipher. Discuss. Problem 5:. (a) The ciphertext ONXM was encrypted by a Hill cipher with a 2 x 2 matrix. The plaintext is null. Find the encryption matrix. (b) Suppose the ciphertext is PNXM and the plaintext is still null. Find the encryption matrix. Note that the first column of the matrix is changed. What does it mean? Is it a good or a bad property of a cipher. Discuss