SQL Server

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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SQL Server

--
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    DECLARE @sTmp0 nvarchar(4000)
    DECLARE @success int
    SELECT @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.

    DECLARE @dkim int
    EXEC @hr = sp_OACreate 'Chilkat.Dkim', @dkim OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    --  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.
    EXEC sp_OAMethod @dkim, 'PrefetchPublicKey', @success OUT, 'myselector', 'example.com'
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @dkim, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @dkim
        RETURN
      END

    PRINT 'Public key prefetched from DNS and cached.'

    EXEC @hr = sp_OADestroy @dkim


END
GO