Rectify solution for 3c

exam/ex.tex

@@ -167,9 +167,14 @@
       $P$.
 
     \item In order for $(x,y)$ to be a valid preimage for the compression
-      function $F^P$, $x$ must be of size $\unit[655]{bits}$ ($=e$ in the
-      diagram) and $y$ must be of size $\unit[101]{bits}$. Furthermore, the
-      following condition must be true: $[F^P(x)=y]\vee [F^P(y)=x]$.
+      function $F^P$, $x$ must be of size $\unit[800]{bits}$ and contain 55
+      zeros at the beginning and 90 zeros at the end. The 655 bits in-between
+      can be modified by an adversary to achieve the required target. Similarly,
+      $y$ must be of size $\unit[800]{bits}$ where the first 50 and the last 649
+      bits are discarded. The bits in-between must be 101 zeros to satisfy our
+      target image. Furthermore, the following condition must be true to achieve
+      a valid preimage: $[F^P(x)=y]$ where $x$ and $y$ satisfy the
+      aforementioned conditions.
 
     \item \TODO