Create a DKIM-Signature for a MIME Message

See more DKIM / DomainKey Examples

Demonstrates the Chilkat Dkim.DkimSign method, which creates a DKIM-Signature header and prepends it to a complete MIME message held in a BinData, modifying it in place. The DkimAlg, DkimCanon, DkimDomain, DkimSelector, DkimHeaders, and DkimBodyLengthCount properties configure the generated signature.

Note: The file paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.BinData,
  Chilkat.PrivateKey,
  Chilkat.Dkim;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  dkim: TDkim;
  privKey: TPrivateKey;
  mimeData: TBinData;

begin
  success := False;

  //  Demonstrates the Dkim.DkimSign method, which creates a DKIM-Signature header and prepends it to
  //  a complete MIME message.  The only argument is a BinData holding the MIME, which is modified in
  //  place.
  //  
  //  The DkimAlg, DkimCanon, DkimDomain, DkimSelector, DkimHeaders, and DkimBodyLengthCount
  //  properties configure the signature that is generated.

  dkim := TDkim.Create;

  //  Configure the DKIM signature.
  dkim.DkimDomain := 'example.com';
  dkim.DkimSelector := 'myselector';

  //  Signing algorithm written to the a= tag.
  dkim.DkimAlg := 'rsa-sha256';

  //  Canonicalization for headers and body, written to the c= tag.
  dkim.DkimCanon := 'relaxed/relaxed';

  //  Colon-separated list of header fields to sign, written to the h= tag.
  dkim.DkimHeaders := 'From:To:Subject:Date:Message-ID';

  //  Maximum number of canonicalized body bytes to hash.  0 means the entire body.
  dkim.DkimBodyLengthCount := 0;

  //  Load the RSA private key and give it to the Dkim object.
  privKey := TPrivateKey.Create;
  success := privKey.LoadPemFile('qa_data/dkim_private.pem');
  if (success = False) then
    begin
      WriteLn(privKey.LastErrorText);
      Exit;
    end;
  success := dkim.SetDkimPrivateKey(privKey);
  if (success = False) then
    begin
      WriteLn(dkim.LastErrorText);
      Exit;
    end;

  //  Load the complete MIME message to be signed.  It must already contain all headers, transfer
  //  encodings, MIME boundaries, and body bytes.
  mimeData := TBinData.Create;
  success := mimeData.LoadFile('qa_data/message.eml');
  if (success = False) then
    begin
      WriteLn(mimeData.LastErrorText);
      Exit;
    end;

  //  Sign.  The DKIM-Signature header is prepended to the MIME in place.
  success := dkim.DkimSign(mimeData);
  if (success = False) then
    begin
      WriteLn(dkim.LastErrorText);
      Exit;
    end;

  //  Save the signed message.
  success := mimeData.WriteFile('qa_output/signed.eml');
  if (success = False) then
    begin
      WriteLn(mimeData.LastErrorText);
      Exit;
    end;
  WriteLn('Message signed.');


  dkim.Free;
  privKey.Free;
  mimeData.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.