PHP ActiveX

Prefetch a DKIM Public Key from DNS

Demonstrates the Chilkat Dkim.PrefetchPublicKey method, which retrieves a DKIM public key from DNS and caches it for a specific selector and domain. The arguments are the selector and the domain. The TXT lookup is made at selector._domainkey.domain.

Background: DkimVerify already fetches the key from DNS on demand, so prefetching is about when the lookup happens: doing it up front lets you separate a potentially slow network step from the verification itself, warm the cache before a batch of messages from the same domain, or confirm the key is publishable before relying on it. After a successful prefetch, verification of a matching signature uses the cached key with no further DNS traffic.

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<?php

$success = 0;

//  Demonstrates the Dkim.PrefetchPublicKey method, which retrieves a DKIM public key from DNS and
//  caches it for a specific selector and domain.  The 1st argument is the selector and the 2nd is
//  the domain.

$dkim = new COM("Chilkat.Dkim");

//  Retrieve the public key from the DNS TXT record at selector._domainkey.domain and cache it.
//  A later DkimVerify for the same selector and domain then uses the cached key.
$success = $dkim->PrefetchPublicKey('myselector','example.com');
if ($success == 0) {
    print $dkim->LastErrorText . "\n";
    exit;
}

print 'Public key prefetched from DNS and cached.' . "\n";

?>