Re: [dnsext] DNSSEC, robustness, and several DS records

"George Barwood" <george.barwood@blueyonder.co.uk> Wed, 11 May 2011 17:28 UTC

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From: "George Barwood" <george.barwood@blueyonder.co.uk>
To: "Paul Hoffman" <paul.hoffman@vpnc.org>, "Stephane Bortzmeyer" <bortzmeyer@nic.fr>
References: <20110511080159.GA13132@nic.fr> <63381BB3-7552-4721-B334-CFE292AA9465@vpnc.org>
Date: Wed, 11 May 2011 18:28:17 +0100
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Cc: dnsext@ietf.org
Subject: Re: [dnsext] DNSSEC, robustness, and several DS records
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>   If there is a known preimage attack on SHA-1 that reduces its
>   effective strength to less than 128 bits,
>   validator implementations SHOULD ignore DS RRs containing SHA-1
>   digests if DS RRs with SHA-256 digests are present in the DS RRset.

The problem is that we don't know if such attacks exist, and more practically
it's hard to update software. So it seems better to plan for the worst.

Besides, implementations may want to use dual algorithms, for example
elliptic curve plus RSA with a moderate size key, on the basis that it's
unlikely that anyone would be able to break both.

I really doubt having resolvers trying to fix up data errors is the way forward.

I think the real fix for mishaps uploading DS records is to have better
in-protocol support. The proposed CDS RRtype is aimed at this :

http://www.ietf.org/mail-archive/web/dnsext/current/msg10900.html

George