eio: periodically feed entropy

rng/eio/dune

@@ -1,3 +1,4 @@
 (library
  (name mirage_crypto_rng_eio)
- (libraries eio cstruct logs mirage-crypto-rng))
+ (libraries eio cstruct logs mirage-crypto-rng duration 
+            mtime.clock.os))

rng/eio/mirage_crypto_rng_eio.ml

@@ -17,9 +17,37 @@ let getrandom_init env i =
   let data = getrandom env 128 in
   Entropy.header i data
 
+let periodic env sw f delta =
+  let clock = Eio.Stdenv.clock env in
+  let rec loop () = 
+    f ();
+    Eio.Time.sleep clock (Duration.to_f delta);
+    loop ()
+  in 
+  Eio.Fiber.fork ~sw loop
+
+let periodically_feed_entropy env sw delta source = 
+  let task () = 
+    let per_pool = 8 in
+    let size = per_pool * pools None in
+    let random = getrandom env size in
+    let idx = ref 0 in
+    let f () = 
+      incr idx;
+      Cstruct.sub random (per_pool * (pred !idx)) per_pool
+    in
+    Entropy.feed_pools None source f
+  in 
+  periodic env sw task delta
+
+let rdrand_task env sw delta = 
+  match Entropy.cpu_rng with
+  | Error `Not_supported -> ()
+  | Ok cpu_rng -> periodic env sw (cpu_rng None) delta
+
 let running = ref false 
 
-let initialize env = 
+let initialize ?(sleep = Duration.of_sec 1) (env: Eio.Stdenv.t) sw = 
   if !running then 
     Log.debug
       (fun m -> m "Mirage_crypto_rng_eio.initialize has already been called, \
@@ -37,6 +65,9 @@ let initialize env =
         Entropy.[ bootstrap ; whirlwind_bootstrap ; bootstrap ; getrandom_init env ] in
       List.mapi (fun i f -> f i) init |> Cstruct.concat
     in 
-    let _ = Entropy.register_source "getrandom" in
-    set_default_generator (create ~seed (module Fortuna))
+    let rng = create ~seed ~time:Mtime_clock.elapsed_ns (module Fortuna) in
+    set_default_generator rng;
+    rdrand_task env sw sleep;
+    let source = Entropy.register_source "getrandom" in
+    periodically_feed_entropy env sw (Int64.mul sleep 10L) source
   end 

rng/eio/mirage_crypto_rng_eio.mli

@@ -4,8 +4,12 @@
     [Eio.Stdenv.secure_random] is used as the [getrandom()] implementation.
 *)
 
-(** [initialize env] will bring the RNG into a working state. *)
-val initialize : Eio.Stdenv.t -> unit 
+(** [initialize ~sleep env sw] will bring the RNG into a working state. The argument
+    [sleep] is measured in ns (default 1s), and used to sleep between collection
+    of entropy from the CPU RNG, every [10 * sleep] getrandom is used to collect
+    entropy.
+*)
+val initialize : ?sleep:int64 -> Eio.Stdenv.t -> Eio.Switch.t -> unit 
 
 (** [getrandom env size] returns a buffer of [size] filled with random bytes. *)
 val getrandom: Eio.Stdenv.t -> int -> Cstruct.t