PHP

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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<?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 S/MIME detached signature.  The object becomes a multipart/signed entity with the
    // original content and a separate signature part.
    $mime->AddDetachedSignature($cert);

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

echo "Detached signature added.\n";