Lemma HMAC_DRBG_generate_helper_Z_Zlength_snd: forall HMAC key v z, 0 <= z -> (forall x y, Zlength (HMAC x y) = 32) -> (exists n, z = n * 32) -> Zlength (snd (HMAC_DRBG_generate_helper_Z HMAC key v z)) = z.