Source file Hkdf.ml

(* Claude Code
 *
 * Copyright (C) 2026 Yoann Padioleau
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public License
 * (LGPL) as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 *)

(* See Hkdf.mli *)

let extract ~(hmac : string -> string -> string) ~(salt : string) (ikm : string) : string = hmac salt ikm

let expand ~(hmac : string -> string -> string) (prk : string) ~(info : string) (length : int) : string =
  let out = Buffer.create length in
  let rec go t i =
    if Buffer.length out < length then (
      let t = hmac prk (t ^ info ^ String.make 1 (Char.chr i)) in
      Buffer.add_string out t;
      go t (i + 1))
  in
  go "" 1;
  Buffer.sub out 0 length