Tcl

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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Tcl


load ./chilkat.dll

set 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.

set 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.
set success [CkDkim_PrefetchPublicKey $dkim "myselector" "example.com"]
if {$success == 0} then {
    puts [CkDkim_lastErrorText $dkim]
    delete_CkDkim $dkim
    exit
}

puts "Public key prefetched from DNS and cached."

delete_CkDkim $dkim