(* ------------------------------------------------ *)
(* Lemma 2: |M1| = |M2| -> |Pad(M1)| = |Pad(M2)| *)

Theorem length_equal_pad_length : forall (msg1 : list byte) (msg2 : list byte),
Zlength msg1  = Zlength msg2 ->
Zlength (generate_and_pad msg1) = Zlength (generate_and_pad msg2).