Exercise $2$:

a$)$ Using Hill cipher encrypt the plaintext "meeting postponed". The key matrix, $K$ and its

inverse are given as: $K=\left[\begin{array}{ccc}6& 24& 1\\ 13& 16& 10\\ 20& 17& 15\end{array}\right]$;$K^{-1}=\left[\begin{array}{ccc}8& 5& 10\\ 21& 8& 21\\ 21& 12& 8\end{array}\right]($modulo $26)$

b$)$ Using the above Hill cipher's information, decrypt the ciphertext: QRTWNFJVV