Implement encryption oracle for challenge 11.

src/main.rs

@@ -1,6 +1,7 @@
 mod bytes;
 mod bytes_base64;
 mod cbs;
+mod ecb;
 mod set1;
 mod set2;
 
@@ -13,7 +14,7 @@ fn main() {
     // set1::challenge6();
     // set1::challenge7();
     // set1::challenge8();
-    // set2::challenge9();
+    set2::challenge9();
     set2::challenge10();
     set2::challenge11();
 }