Re: [DNSOP] One Chair's comments on draft-wessels-dns-zone-digest

["Paul Hoffman" <[e-mail]>]

On 2 Aug 2018, at 19:50, Paul Wouters wrote:

> On Thu, 2 Aug 2018, Paul Hoffman wrote:
>
>>>  Note that the checksum in this case must be at least as
>>>  cryptographically strong as the signature algorithm used
>>>  in the individual RRSIGs/DNSKEYs.
>>
>> Not true.
>>
>> If the resolver is validating, the ZONEMD only adds assurance that 
>> the non-signed records are there. Thus, the hash algorithm for the 
>> zone is unrelated to the hash algorithms in the signatures.
>
> Then don't cover signed RRsets with ZONEMD. Then this problem goes 
> away,
> and you force implementations to validate all records before putting
> them in the cache.

That only works for validating resolvers. ZONEMD also is useful for 
non-validating resolvers.

>> If the resolver is not validating, the ZONEMD assures that all the 
>> records are there. The strength of that assurance is the same as the 
>> second pre-image strength of the hash. However, the resolver cannot 
>> say "oh, look, now I can start resolving with what I got in the zone 
>> transfer": it still needs to validate every RRSIG all the way to the 
>> root.
>
> That's not what people are going to do. They are going to grab the
> AXFR'ed data, check the checksum and throw it in the "validated" cache
> and they won't revalidate every root zone entry they are about to 
> serve.

A non-validating resolver doesn't have a validated cache.

--Paul Hoffman