Subject: [DNSOP] Can an RRSET remain valid past the expiration timestamp on its signing RRSIG?

From: Nick Johnson <[email-masked]>
Date: Wed, 24 Jul 2019 17:50:04 +1200

Suppose I receive a response containing an RRSET with records with
ttl=3600, signed with an RRSIG that has an expiration timestamp 60 seconds
from now.

After validating the signature, can I cache the RRSET for 3600 seconds, or
only for 60 seconds? If the former, and the RRSET is a DNSKEY, can I rely
on it to validate other RRSIGs for the entire 3600 seconds?

-Nick Johnson

---

From: Matthijs Mekking <[email-masked]>
Date: Wed, 24 Jul 2019 08:29:11 +0200

RFC 4035 says:

   If the resolver accepts the RRset as authentic, the validator MUST
   set the TTL of the RRSIG RR and each RR in the authenticated RRset to
   a value no greater than the minimum of:

   o  the RRset's TTL as received in the response;

   o  the RRSIG RR's TTL as received in the response;

   o  the value in the RRSIG RR's Original TTL field; and

   o  the difference of the RRSIG RR's Signature Expiration time and the
      current time.

That last bullet point tells that if the signature's expiration time is
smaller than the TTLs received in the response, the RRset is cached for
at most the duration until the signature expires.

On 7/24/19 7:50 AM, Nick Johnson wrote:
> ttl=3600, signed with an RRSIG that has an expiration timestamp 60
> seconds from now.
> 
> After validating the signature, can I cache the RRSET for 3600 seconds,
> or only for 60 seconds? If the former, and the RRSET is a DNSKEY, can I
> rely on it to validate other RRSIGs for the entire 3600 seconds?

In your example, the RRset must be cached for at most 60 seconds.

Best regards,

Matthijs

> 
> -Nick Johnson
> 
> _______________________________________________
> DNSOP mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/dnsop
>

---

From: Nick Johnson <[email-masked]>
Date: Thu, 25 Jul 2019 09:27:51 +1200

Thank you both.