Local Open Scope nat.
Definition LBLOCK : nat := Z.to_nat LBLOCKz.
Definition CBLOCK : nat := Z.to_nat CBLOCKz.
Opaque LBLOCK CBLOCK.

Lemma length_hash_blocks: forall regs blocks,
length regs = 8%nat ->
(LBLOCKz | Zlength blocks) ->
length (hash_blocks regs blocks) = 8%nat.