(*
  HMAC plugin.
  Copyright (C) 2012-2014 Silvio Clecio.

  Please see the LICENSE file.
*)

unit HMAC;

{$mode objfpc}{$H+}

interface

uses
  SHA1;

const
  HEX_TABLE: array[0..15] of Char = '0123456789abcdef';
  SHA1_BLOCK_SIZE = 64;
  SHA1_BLOCK_COUNT = 20;

function SHA1Raw(const ABuffer; const ABufferLength: PtrUInt): string;
function HMACSHA1(const AKey, AMessage: string): string;

implementation

function SHA1Raw(const ABuffer; const ABufferLength: PtrUInt): string;
var
  I: Byte;
  VDest: PChar;
  VDigest: TSHA1Digest;
  VContext: TSHA1Context;
begin
  SHA1Init(VContext);
  SHA1Update(VContext, ABuffer, ABufferLength);
  SHA1Final(VContext, VDigest);
  SetLength(Result, SHA1_BLOCK_COUNT);
  VDest := Pointer(Result);
  for I := 0 to SHA1_BLOCK_COUNT - 1 do
  begin
    VDest^ := Char(VDigest[I]);
    Inc(VDest);
  end;
end;

function HMACSHA1(const AKey, AMessage: string): string;
var
  I: Byte;
  VDest: PChar;
  VLenght: PtrUInt;
  VDigest: TSHA1Digest;
  VKey, VOPad, VIPad: string;
begin
  VLenght := Length(AKey);
  if VLenght > SHA1_BLOCK_SIZE then
  begin
    SetLength(VKey, SHA1_BLOCK_SIZE);
    FillChar(Pointer(VKey)^, SHA1_BLOCK_SIZE, #0);
    VKey := SHA1Raw(Pointer(AKey)^, VLenght) + VKey;
  end
  else
  begin
    SetLength(VKey, SHA1_BLOCK_SIZE - VLenght);
    FillChar(Pointer(VKey)^, SHA1_BLOCK_SIZE - VLenght, #0);
    VKey := AKey + VKey;
  end;
  SetLength(VOPad, SHA1_BLOCK_SIZE);
  FillChar(Pointer(VOPad)^, SHA1_BLOCK_SIZE, $5c);
  SetLength(VIPad, SHA1_BLOCK_SIZE);
  FillChar(Pointer(VIPad)^, SHA1_BLOCK_SIZE, $36);
  for I := 1 to SHA1_BLOCK_SIZE do
  begin
    VOPad[I] := Char(Byte(VOPad[I]) xor Byte(VKey[I]));
    VIPad[I] := Char(Byte(VIPad[I]) xor Byte(VKey[I]));
  end;
  VIPad := VIPad + AMessage;
  VDigest := SHA1String(VOPad + SHA1Raw(Pointer(VIPad)^, Length(VIPad)));
  SetLength(Result, SHA1_BLOCK_COUNT * 2);
  VDest := Pointer(Result);
  for I := 0 to SHA1_BLOCK_COUNT - 1 do
  begin
    VDest[0] := HEX_TABLE[(VDigest[I] shr 4) and 15];
    VDest[1] := HEX_TABLE[VDigest[I] and 15];
    Inc(VDest, 2);
  end;
end;

end.