Prefetch a DKIM Public Key from DNS

See more DKIM / DomainKey Examples

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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#include <C_CkDkim.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkDkim dkim;

    success = FALSE;

    //  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 = CkDkim_Create();

    //  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 = CkDkim_PrefetchPublicKey(dkim,"myselector","example.com");
    if (success == FALSE) {
        printf("%s\n",CkDkim_lastErrorText(dkim));
        CkDkim_Dispose(dkim);
        return;
    }

    printf("Public key prefetched from DNS and cached.\n");


    CkDkim_Dispose(dkim);

    }