PHP

Create an Opaque (Attached) S/MIME Signature

Demonstrates the Chilkat Mime.ConvertToSigned method, which creates an opaque (attached) S/MIME signature. The only argument is the signing Cert. On success the entity is replaced by a CMS/PKCS #7 signed-data structure that wraps the content inside the 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.

Background: An opaque signature bundles the content inside the CMS structure, so the message is a single application/pkcs7-mime blob that only S/MIME-aware software can read. It is more tamper-resistant in transit — nothing can alter the content without breaking the wrapper — at the cost of the backward compatibility a detached signature offers. Use it when every recipient is known to support S/MIME.

Chilkat PHP Downloads

Download Chilkat for PHP

Chilkat2 PHP

<?php

use Chilkat2\Cert;
use Chilkat2\Mime;

$mime = new Mime();
try {
    $mime->SetBodyFromPlainText('This message will be signed.');

    // 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 = new Cert();
    $cert->LoadPfxFile('qa_data/signer.pfx', $pfxPassword);

    // Create an OPAQUE (attached) S/MIME signature.  The entity is replaced by a CMS/PKCS #7
    // signed-data structure that wraps the content inside the signature.
    $mime->ConvertToSigned($cert);

    $mime->SaveMime('qa_output/signed_opaque.eml');
} catch (\Chilkat2\Exception $e) {
    echo $e->getMessage(), "\n";
    exit;
}

echo "Message converted to an opaque signed message.\n";