Add computational hiding for 5d

exam/ex.tex

@@ -330,6 +330,11 @@
       two different graphs to the same output which corresponds to solving the
       CGI problem.
 
+      Computational hiding: Two commitments are computationally
+      indistinguishable from each other as long as the adversary is PPT.
+      Otherwise, the adversary could distinguish between the two distribution
+      ensembles.
+
     \item If $G_{ch}=\phi_{ch}(G)$ and $G'=\psi(G)$, it follows that
       $G=\phi_{ch}^{-1}(G_{ch})$ and therefore $G'=\psi(\phi_{ch}^{-1}(G_{ch}))$
       so the verifier will always accept.