Re: [DNSOP] Whiskey Tango Foxtrot on key lengths...

Phillip Hallam-Baker <> Thu, 27 March 2014 14:58 UTC

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Date: Thu, 27 Mar 2014 10:58:49 -0400
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From: Phillip Hallam-Baker <>
To: Joe Abley <>
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Cc: dnsop WG <>, Nicholas Weaver <>
Subject: Re: [DNSOP] Whiskey Tango Foxtrot on key lengths...
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The NIST Guidance is from 2009. It is long since obsolete.

This is one of the reasons why we need to take advice on crypto algorithms
in house and make them IETF wide. Which is why I was asked to write this:

Having DNSSEC use 1024 bit RSA when we know it is unsafe sends a really bad
message. We are currently phasing out use of 1024 bit crypto in the Web PKI
for far less core concerns than the DNS roots.

This is one of the reasons why I am proposing support for multi-packet UDP
responses in PRIVATE-DNS. I am not sure that they are necessary. It might
well be that 1500 bytes is sufficient for all DNS messages as argued here.
But right now we have people making really bad decisions because of a
design constraint.

If we are going to encrypt messages that is going to eat up a few bytes in
each packet no matter what we do. IPSEC consumes quite a few bytes.

Trying to dance round this constraint is not making the protocol any
simpler. All it is doing is pushing the complexity balloon down in one
place and have bits pop out all over the place.

On Thu, Mar 27, 2014 at 10:22 AM, Joe Abley <> wrote:

> On 27 Mar 2014, at 22:56, Nicholas Weaver <>
> wrote:
> > Bits are not precious:  Until a DNS reply hits the fragmentation limit
> of ~1500B, size-matters-not (tm, Yoda Inc).
> >
> > So why are both root and com and org and, well, just about everyone else
> using 1024b keys for the actual signing?
> Those requirements (for the root zone keys) came from NTIA via NIST:
> (well, NIST specified a minimum key size, but the implication at the time
> was that that was a safe minimum).
> Bear in mind, I guess, that these keys have a publication lifetime that is
> relatively short. The window in which a factoring attack has an opportunity
> to find a result that can be exploited as a compromise is fairly narrow.
> Joe
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