4. A message is enciphered using a product cipher that consists of one Hill cipher followed by (composed with) another Hill cipher. Each of these Hill ciphers uses a 4 x 4 matrix that is invertible modulo 26. a. Use a theorem from linear algebra to explain why the product cipher has a well defined inverse (deciphering) function. b. Is the product cipher more secure, less secure or just as secure as a single Hill cipher? Justify your answer 4. A message is enciphered using a product cipher that consists of one Hill cipher followed by (composed with) another Hill cipher. Each of these Hill ciphers uses a 4 x 4 matrix that is invertible modulo 26. a. Use a theorem from linear algebra to explain why the product cipher has a well defined inverse (deciphering) function. b. Is the product cipher more secure, less secure or just as secure as a single Hill cipher? Justify your