Re: [Doh] [Ext] Does the HTTP freshness lifetime need to match the TTL?

Paul Hoffman <paul.hoffman@icann.org> Mon, 14 May 2018 13:04 UTC

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From: Paul Hoffman <paul.hoffman@icann.org>
To: Tony Finch <dot@dotat.at>, Miek Gieben <miek@miek.nl>
CC: DoH WG <doh@ietf.org>
Thread-Topic: [Doh] [Ext] Does the HTTP freshness lifetime need to match the TTL?
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Date: Mon, 14 May 2018 13:03:56 +0000
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Subject: Re: [Doh] [Ext] Does the HTTP freshness lifetime need to match the TTL?
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On May 14, 2018, at 4:15 AM, Tony Finch <dot@dotat.at> wrote:
> 
> Paul Hoffman <paul.hoffman@icann.org> wrote:
>> 
>> To me, "may use the time remaining before expiration" does not sound a
>> requirement, or even an expectation.
> 
> RFC 4035, section 5.3.3
> 
>   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.

Ouch. (Note to HTTP folks: you're not the only ones with RFCs whose text does not always line up.)

Proposed addition:
   If the DNS API Server is also Security-Aware Resolver ([RFC4033] Section 2),
   the explicit freshness time MUST be set based on [RFC4035] Section 5.3.3.

--Paul Hoffman