Dart

Get the S/MIME Signer's Certificate

Demonstrates the Chilkat Mime.LastSignerCert method, which loads the signer certificate at a zero-based index from the most recent successful verification (or security-unwrapping) into a Cert. The first argument is the signer index and the second is the receiving Cert.

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: Verifying tells you the signature is mathematically valid, but you usually also need to know who signed — the subject, the issuer, the validity dates — to decide whether to trust it. This retrieves each signer's certificate after verification so your code can inspect and apply its own trust rules. A message can have multiple signers, so iterate from 0 to NumSignerCerts - 1.

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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  final mime = CkMime();
  try {
    mime.loadMimeFile('qa_data/signed.eml');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // After a successful verification, load each signer's certificate to inspect it.  The 1st argument
  // is the zero-based signer index and the 2nd is a Cert object that receives the certificate.
  try {
    mime.verify();
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  final n = mime.numSignerCerts;
  final cert = CkCert();
  for (var i = 0; i < n; i++) {
    try {
      mime.lastSignerCert(i, cert);
    } on ChilkatException catch (e) {
      print(e.lastErrorText);
      return;
    }

    print('Signer $i: ${cert.subjectCN} (issued by ${cert.issuerCN})');
  }
}