Delphi ActiveX

Add an S/MIME Detached Signature

Demonstrates the Chilkat Mime.AddDetachedSignature method, which creates an S/MIME detached signature. The only argument is the signing Cert, which must have access to its private key. On success the entity becomes a multipart/signed with the content and a separate signature part.

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.

Background: A detached signature (multipart/signed) keeps the original content readable alongside a separate signature part — so recipients whose software does not understand S/MIME still see the message, they just cannot verify it. That backward compatibility makes detached the usual choice for signed email. The signer proves authorship with a certificate that carries its private key.

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var
success: Integer;
mime: TChilkatMime;
pfxPassword: WideString;
cert: TChilkatCert;

begin
success := 0;

mime := TChilkatMime.Create(Self);
success := mime.SetBodyFromPlainText('This message will be signed.');
if (success = 0) then
  begin
    Memo1.Lines.Add(mime.LastErrorText);
    Exit;
  end;
//  Load the signing certificate (which must have access to its private key) from a PFX file.
//  The PFX password should come from a secure source rather than being hard-coded.
pfxPassword := 'myPfxPassword';
cert := TChilkatCert.Create(Self);
success := cert.LoadPfxFile('qa_data/signer.pfx',pfxPassword);
if (success = 0) then
  begin
    Memo1.Lines.Add(cert.LastErrorText);
    Exit;
  end;

//  Create an S/MIME detached signature.  The object becomes a multipart/signed entity with the
//  original content and a separate signature part.
success := mime.AddDetachedSignature(cert.ControlInterface);
if (success = 0) then
  begin
    Memo1.Lines.Add(mime.LastErrorText);
    Exit;
  end;

success := mime.SaveMime('qa_output/signed.eml');
if (success = 0) then
  begin
    Memo1.Lines.Add(mime.LastErrorText);
    Exit;
  end;
Memo1.Lines.Add('Detached signature added.');