Now Bob should follow the following steps to decrypt the message
1) First he should arrange the input vector in the form of a 3X3 matrix i.e the first 3 elements form the first column, the next three elements form the second column and so on.
Thus he would get
A= $ \left[ \begin{matrix}1 & 0 & 4 \\ 0 & 1 & 0 \\ 1 & 0 & 1\end{matrix} \right] $
