Let F be a secure block cipher and consider instantiating Enc$-$then$-$MAC with: our favorite CPA$-$secure encryption Enc$($k$,$m$)=($r$,$F$($k$,$r$)$m$).-$ CBC$-$MAC restricted to $2-$block inputs $($construction $10\mathrm{.}5)$ The encryption scheme is CPA$-$secure and the MAC is also a secure MAC since it is used on inputs of only $2$ blocks $($ciphertexts of the encryption scheme$).$ Because of this Enc$-$then$-$MAC will result in a CCA$-$secure scheme. Show that the result is not CCA$-$secure when the same key $($and same F $)$ is used for both the encryption $\backslash$& MAC!