Subject: Re: DJB about NSEC3

From: Mark Andrews <[email-masked]>
Date: Tue, 02 Sep 2008 21:23:59 +1000

> 
> > 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 t
> ha
> > t
> > 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.
> > 
> > 	Bert
> 
> 	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

	All importantbank.com has to do is not have insecure delegations.

	Mark
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: [email-masked]

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