This is a discussion on Re: DJB about NSEC3 - DNS ; > On Tue, Sep 02, 2008 at 09:50:15AM +0100, Roy Arends wrote: > > I'd like to have more information how the "NSEC3" variant of DNSSEC is > > almost always breakable? I'd like to know how to interpret "almost ...
> On Tue, Sep 02, 2008 at 09:50:15AM +0100, Roy Arends wrote:
> > I'd like to have more information how the "NSEC3" variant of DNSSEC is
> > almost always breakable? I'd like to know how to interpret "almost always
> > breakable".
> I think it has been established that NSEC(3) allows the creation of
> non-existent names within secured zones, if I followed things directly.
> So even if importantbank.com is signed, I can try to spoof in
> NS records for secure.importantbank.com, using a purloined NSEC(3) record tha
> covers secure.importantbank.com. The secure.importantbank.com zone is then
> unsigned, and contains the data of my choice.
> As long as secure.importantbank.com does not exist already of course.
> As a precautionary measure, importantbank.com might want to have dummy
> records for everything that 'looks' official.
Assuming the optout is not in use.
You can't bring a secure delegation into existance under a
NSEC3 zone and have the subzone validate. NSEC3 is as
strong as NSEC for this case.
You can bring a insecure delegation into existance iff there
is another insecure delegation and the hash of the name
your are trying to bring into existance matches the hash
of a existing insecure delegation.
Given the it's a sha1 hash that's n in 2^160 for the hash
of any abitrary name matching one a existing nsec3 hash where
n is the number of insecure delegations.
For all practical purposes this is impossible.
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: Mark_Andrews@isc.org
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