Lemma HMAC_DRBG_generate_helper_Z_Zlength_fst:
forall HMAC key v z,
0 <= z ->
Zlength v = 32 ->
(forall x y, Zlength (HMAC x y) = 32) ->
Zlength (fst (HMAC_DRBG_generate_helper_Z HMAC key v z)) = 32.