The interactive protocol for $\overline{\text { GIso }}$ of Example 10.1 is not perfect zero-knowledge, because a verifier $M_{v^{\prime}}$ may send a graph $G^{\prime}$ to the prover that is not randomly generated from $G_1$ or $G_2$ and gain information of whether $G^{\prime}$ is isomorphic to $G_1$ or $G_2$. Modify this interactive protocol to a perfect zero-knowledge proof system for $\overline{\text { GIso. }}$