Q$7$: KeyGen ${?}_4,$ Tag ${?}_4,$ Verify $\{$:${?}_4)$ is defined as follows:

KeyGen ${?}_4$ is identical to KeyGen ${?}_1,$ and it outputs a key $k.$

$Ta{g}_4[k,(m_1,m_2)]$ first runs $Ta{g}_1(k,m_1)$ and obtains ${}_1$ and it

runs $Ta{g}_2(k,m_2)$ and obtains ${}_2.$ The final tag is

$$:$={}_{1}o+{}_2$

Is ${}_4$ a secure MAC? Briefly explain why. $(10$ pts$)$