Dart

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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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  final mime = CkMime();
  try {
    mime.setBodyFromPlainText('This message will be signed.');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // 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.
  final pfxPassword = 'myPfxPassword';
  final cert = CkCert();
  try {
    cert.loadPfxFile('qa_data/signer.pfx', pfxPassword);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Create an S/MIME detached signature.  The object becomes a multipart/signed entity with the
  // original content and a separate signature part.
  try {
    mime.addDetachedSignature(cert);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  try {
    mime.saveMime('qa_output/signed.eml');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('Detached signature added.');
}