Java

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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Java

import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    boolean 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.

    CkDkim dkim = new CkDkim();

    //  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 == false) {
        System.out.println(dkim.lastErrorText());
        return;
        }

    System.out.println("Public key prefetched from DNS and cached.");
  }
}