PHP

Send an Email with a Digital Signature

Demonstrates the Chilkat Email.SendSigned property. Set it to true to have the email sent with a digital signature (the default is false). Signing also requires a certificate with access to its private key. This example loads that certificate (and its private key) from a PFX file with Cert.LoadPfxFile, supplies it via SetSigningCert, and enables signed sending.

Background: Signing is the mirror image of encrypting. To encrypt for a recipient you use their public certificate; to sign you use your own private key, and recipients verify with your public certificate. A signature does not hide the message — a signed email is still readable by anyone — but it proves who sent it and guarantees the content was not tampered with. A PFX (also called PKCS#12, .pfx or .p12) is a password-protected file that bundles a certificate together with its private key, making it a convenient single-file source for signing credentials.

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<?php

use Chilkat2\Cert;
use Chilkat2\Email;

// Demonstrates the Email.SendSigned property with a full signing setup.  Set SendSigned
// to true to have the email sent with a digital signature.  Signing requires a certificate
// with access to its private key, which we load here from a PFX (.pfx / .p12) file.

$email = new Email();
$email->Subject = 'Signed email';
$email->Body = 'This message will be sent with a digital signature.';
$email->From = 'alice@example.com';
$email->AddTo('Bob', 'bob@example.com');

// Load the signing certificate (including its private key) from a PFX file.
// The 2nd argument is the PFX password.
$cert = new Cert();
try {
    $cert->LoadPfxFile('qa_data/certs/signer.pfx', 'pfx_password');

    // Provide the signing certificate.
    $email->SetSigningCert($cert);
} catch (\Chilkat2\Exception $e) {
    echo $e->getMessage(), "\n";
    exit;
}

// Request that the email be sent with a digital signature.
$email->SendSigned = true;

echo 'SendSigned = ', ($email->SendSigned ? 'true' : 'false'), "\n";

// Note: The path "qa_data/certs/signer.pfx" is a relative local filesystem path,
// relative to the current working directory of the running application.