Re: [DNSOP] Comments regarding the NSEC5

[Jan Včelák <[e-mail]>]

On 11.3.2015 17:30, Florian Weimer wrote:
> On 03/11/2015 05:19 PM, Jan Včelák wrote:
> 
>>> It's not clear if the security goals make sense.  What do zone operators
>>> gain if zone enumeration attacks are moved from offline to online, other
>>> than a need to provision additional server capacity?  It's not that they
>>> can block resolution requests from large resolvers if a part of their
>>> client population participates in aggressive enumeration.
>>
>> It dependes whether you see zone enumeration as a problem.
> 
> If I really want to enumerate a zone, I will just send my dictionary as
> queries, possibly through open resolvers.  People are reckless like
> that.  At least with NSEC3, polite attackers can do some of the
> processing off-line, without punishing authoritative servers or
> resolvers.  NSEC5 takes away that option.  Do the existing enumerators
> care?  Who knows.

I really can't tell. I don't know.

>>> Section 4 says, “NSEC5 hash is an SHA-256 hash function as specified in
>>> [RFC6234].”  Are you sure that's right?
>>
>> You mean the reference to the RFC? Yes, I think it's right. Or am I
>> missing something?
> 
> I'm guessing, but “NSEC5 hash” is probably what involves FDH.  Based on
> your comment,s it's clearly *not* SHA-256, contrary to what I quoted above.

NSEC5 proof is the FDH of domain name.
NSEC5 hash is SHA-256 of NSEC5 proof.

I will clarify that.

>> We deal with NSEC5 proofs and NSEC5 hashes (see the Terminology
>> section). The NSEC5 proof is the FDH (can be comptuted only by the
>> holder of the NSEC5 private key); the NSEC5 hash is an SHA-256 hash of
>> the NSEC5 proof (everyone can compute it, if they know the NSEC5 proof).
>>
>> So in your notation, an NSEC5 RR owner name should be:
>> Base32hex(SHA-256(FDH(Wire-Encode(owner name), privkey)))
> 
> And the inner part (without the Base32 encoding) is the NSEC5 hash?  Or
> is the SHA-256 hash skipped?

Yes, the SHA-256(...) is the NSEC5 hash. The input is NSEC5 proof.

Jan