PHP ActiveX

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

$success = 0;

$mime = new COM("Chilkat.Mime");
$success = $mime->SetBodyFromPlainText('This message will be signed.');
if ($success == 0) {
    print $mime->LastErrorText . "\n";
    exit;
}

//  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 COM("Chilkat.Cert");
$success = $cert->LoadPfxFile('qa_data/signer.pfx',$pfxPassword);
if ($success == 0) {
    print $cert->LastErrorText . "\n";
    exit;
}

//  Create an S/MIME detached signature.  The object becomes a multipart/signed entity with the
//  original content and a separate signature part.
$success = $mime->AddDetachedSignature($cert);
if ($success == 0) {
    print $mime->LastErrorText . "\n";
    exit;
}

$success = $mime->SaveMime('qa_output/signed.eml');
if ($success == 0) {
    print $mime->LastErrorText . "\n";
    exit;
}

print 'Detached signature added.' . "\n";

?>