(*The function occurring in the VST spec of mbedtls' random function ie no additional input*)
Definition mbedtls_generate s I n :=
match mbedtls_HMAC256_DRBG_generate_function s I n []
with ENTROPY.success (bytes, J) ss =>
match J with ((((VV, KK), RC), _), PR) =>
Some (bytes, ss, HMAC256DRBGabs KK VV RC (hmac256drbgabs_entropy_len I) PR
(hmac256drbgabs_reseed_interval I))
end
| _ => None
end.

Lemma fold_vector_length: forall l m,
fold_left
(fun (acc : nat) (a : Vector.t bool 256) =>
(acc + Datatypes.length (Vector.to_list a))%nat) l m =
(m + Datatypes.length l * 256)%nat.