-- HMAC - Provide a comprehensive generic HMAC package that suffices for the SHA family and whatnot.
-- Copyright (C) 2023 Prince Trippy <programmer@verisimilitudes.net>.

-- This program is free software: you can redistribute it and/or modify it under the terms of the
-- GNU Affero General Public License version 3 as published by the Free Software Foundation.

-- This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
-- even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
-- See the GNU Affero General Public License for more details.

-- You should have received a copy of the GNU Affero General Public License along with this program.
-- If not, see <http://www.gnu.org/licenses/>.

generic -- I'm not entirely pleased with these names, or the tighter index specifications.  Oh well.
   type   Unit_Type is mod <>;
   type  Index_Type is range <>;
   type Length_Type is mod <>;
   subtype Block_Range is Index_Type range <>;
   type  Unit_Array is array (Index_Type range <>) of Unit_Type;
   type  Unit_Block is array (Block_Range) of Unit_Type;
   type Status_Type is private;
   type Digest_Type is private;
   Initial_Status_Constant : in Status_Type;
   Inner_Pad, Outer_Pad : in Unit_Block;
   with function To_Unit (Datum : in Digest_Type) return Unit_Array;
   with function Hash (Data : in Unit_Array) return Digest_Type is <>;
   with function Hash (State : in Status_Type; Data : in Unit_Block) return Status_Type is <>;
   with function Hash (State : in Status_Type; Data : in Unit_Array;
                       Unit_Length : in Natural) return Digest_Type is <>;
package HMAC is
   type Prepared_Key is private; -- The name Keypair for this type was considered, but was too poor.

   function Prepare_Key (Key : in Unit_Array) return Prepared_Key;

   function HMAC (Key : in Prepared_Key; Data : in Unit_Array) return Digest_Type;
private
   type Prepared_Key is record Outer_Status, Inner_Status : Status_Type; end record;
end HMAC;
.