unikernel/duniverse/kdf/hkdf/hkdf.ml

@@ -0,0 +1,42 @@
+
+module type S = sig
+  val extract : ?salt:string -> string -> string
+  val expand : prk:string -> ?info:string -> int -> string
+end
+
+module Make (H : Digestif.S) : S = struct
+  let extract ?salt ikm =
+    let key = match salt with
+      | None -> String.make H.digest_size '\x00'
+      | Some x -> x
+    in
+    H.(to_raw_string (hmac_string ~key ikm))
+
+  let expand ~prk ?info len =
+    let info = match info with
+      | None -> ""
+      | Some x -> x
+    in
+    let t n last =
+      let nc = String.make 1 (Char.unsafe_chr n) in
+      H.(to_raw_string (hmac_string ~key:prk (String.concat "" [last ; info ; nc])))
+    in
+    let n = succ (len / H.digest_size) in
+    let rec compute acc count = match count, acc with
+      | c, xs when c > n -> String.concat "" (List.rev xs)
+      | c, x::_ -> compute (t c x :: acc) (succ c)
+      | _, [] -> invalid_arg "can not happen"
+    in
+    let buf = compute [""] 1 in
+    String.sub buf 0 len
+end
+
+let extract ~hash ?salt ikm =
+  let module H = (val (Digestif.module_of_hash' hash)) in
+  let module HKDF = Make (H) in
+  HKDF.extract ?salt ikm
+
+let expand ~hash ~prk ?info len =
+  let module H = (val (Digestif.module_of_hash' hash)) in
+  let module HKDF = Make (H) in
+  HKDF.expand ~prk ?info len