Add solution for 1d

exam/ex.tex

@@ -63,7 +63,11 @@
       function. In total there likely need to be two distinct keys for the block
       cipher calls and one key for the hash function.
 
-    \item \TODO
+    \item Since EWCDM is based on a block cipher and a hash function and because
+      those usually operate on fixed-length inputs, the construction also
+      operates on fixed-length inputs. Messages come in variable-length sizes
+      and need to be padded by the block cipher to the specified block size.
+
     \item \TODO
     \item \TODO
     \item \TODO