[dns-operations] NSEC3 parameter selection (BCP: 1 0 0 -)

[Viktor Dukhovni]

On Mon, Jan 18, 2021 at 05:58:21PM +0100, Vladimír Čunát wrote:

> On 1/18/21 7:57 AM, Viktor Dukhovni wrote:
> > The non-empty salt is pointless, but basically harmless.
> 
> Why should salt be pointless?  Can you hint/link?

Because:

    1.  Every zone is effectively already salted, because as you
        note below the hash covers the FQDN.

    2.  Changing the salt takes some care, so "nobody" does it.

    3.  Combining 1 and 2 we conclude that a fixed salt is no
        better than an empty salt.

> > I find the shared "salt" value somewhat "amusing"
> 
> Whole FQDNs are hashed, so sharing salt among different zones seems safe 
> to me, though I must admit I have no idea why anyone might want to do 
> it.  Though if salt is pointless overall...

See above. :-)  Here are the frequencies of NSEC and NSEC3 parameter
combinations across all TLDs:

     50 NSEC
    177 NSEC3 no opt-out:

         77 NSEC3 1 0 5 salted
         48 NSEC3 1 0 1 salted
         28 NSEC3 1 0 12 salted
         18 NSEC3 1 0 10 salted
          2 NSEC3 1 0 8 salted
          1 NSEC3 1 0 3 salted
          1 NSEC3 1 0 20 salted
          1 NSEC3 1 0 13 salted
          1 NSEC3 1 0 100 salted

    1143 NSEC3 with opt-out:

        482 NSEC3 1 1 1 salted
        191 NSEC3 1 1 100 salted
        152 NSEC3 1 1 10 salted
        145 NSEC3 1 1 0 -
         99 NSEC3 1 1 1 -
         30 NSEC3 1 1 5 salted
         15 NSEC3 1 1 3 salted
          9 NSEC3 1 1 0 salted
          5 NSEC3 1 1 20 salted
          4 NSEC3 1 1 5 -
          2 NSEC3 1 1 8 salted
          2 NSEC3 1 1 25 salted
          2 NSEC3 1 1 150 salted
          1 NSEC3 1 1 2 salted
          1 NSEC3 1 1 17 salted
          1 NSEC3 1 1 15 salted
          1 NSEC3 1 1 12 salted
          1 NSEC3 1 1 10 -

It would be good to see all the iteration counts drop to 10 or less,
ideally just 0.

It would also be good to see opt-out used substantially less frequently,
with just a few of the largest zones (perhaps some day none) using it to
reduce storage overhead and cost of whole-zone signing if delegations
are sufficiently sparsely signed.

-- 
    Viktor.