1. Bob can decrypt the message by multiplying the encrypted message with the inverse of the secret matrix.
2. Eve can not decrypt the message without the inverse of the secret matrix. She does however have all the necessary information to find said inverse.
3. $ \right[ \begin{array}{ccc} 1 & 0 & 4 \\& 0 & 1 & 0 \\& 1 & 0 & 1\end {array} \left $
