Dart

Check if an Email Was Received Digitally Signed

Demonstrates the read-only Chilkat Email.ReceivedSigned property, which is true if the email was originally received carrying one or more digital signatures. Knowing a message was signed is separate from knowing the signature checked out, so this example also reads SignaturesValid to report whether the signed content verified.

Background: A digital signature on an email (S/MIME) provides two things: authenticity (it was really sent by the holder of a particular certificate) and integrity (the content was not altered in transit). The sender signs a hash of the message with their private key; the recipient verifies it with the sender's public certificate. ReceivedSigned simply tells you a signature is present — verifying it is a separate step exposed through SignaturesValid.

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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // Demonstrates the read-only Email.ReceivedSigned property, which is true if this
  // email was originally received with a digital signature.  Use SignaturesValid to
  // determine whether the signed content actually verified.

  final email = CkEmail();

  try {
    email.loadEml('qa_data/eml/signed.eml');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  if (email.receivedSigned) {
    print('This email was received with a digital signature.');
    if (email.signaturesValid) {
      print('All signatures are valid.');
    } else {
      print('One or more signatures are NOT valid.');
    }
  } else {
    print('This email was not signed.');
  }

  // Note: Paths such as "qa_data/..." are relative local filesystem paths,
  // relative to the current working directory of the running application.
}