Re: [dane] Digest Algorithm Agility discussion
Paul Wouters <paul@cypherpunks.ca> Mon, 17 March 2014 16:58 UTC
Return-Path: <paul@cypherpunks.ca>
X-Original-To: dane@ietfa.amsl.com
Delivered-To: dane@ietfa.amsl.com
Received: from localhost (ietfa.amsl.com [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id C79AA1A01ED for <dane@ietfa.amsl.com>; Mon, 17 Mar 2014 09:58:05 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.9
X-Spam-Level:
X-Spam-Status: No, score=-1.9 tagged_above=-999 required=5 tests=[BAYES_00=-1.9] autolearn=ham
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id qIQYnJ-KmuWu for <dane@ietfa.amsl.com>; Mon, 17 Mar 2014 09:58:04 -0700 (PDT)
Received: from bofh.nohats.ca (bofh.nohats.ca [76.10.157.69]) by ietfa.amsl.com (Postfix) with ESMTP id E664A1A0436 for <dane@ietf.org>; Mon, 17 Mar 2014 09:58:03 -0700 (PDT)
Received: from bofh.nohats.ca (bofh.nohats.ca [127.0.0.1]) by bofh.nohats.ca (Postfix) with ESMTP id 48BDF800AA for <dane@ietf.org>; Mon, 17 Mar 2014 12:57:55 -0400 (EDT)
Received: from localhost (paul@localhost) by bofh.nohats.ca (8.14.7/8.14.7/Submit) with ESMTP id s2HGvsCM008140 for <dane@ietf.org>; Mon, 17 Mar 2014 12:57:55 -0400
X-Authentication-Warning: bofh.nohats.ca: paul owned process doing -bs
Date: Mon, 17 Mar 2014 12:57:54 -0400
From: Paul Wouters <paul@cypherpunks.ca>
X-X-Sender: paul@bofh.nohats.ca
To: dane WG list <dane@ietf.org>
In-Reply-To: <20140317155049.GB24183@mournblade.imrryr.org>
Message-ID: <alpine.LFD.2.10.1403171235400.32251@bofh.nohats.ca>
References: <20140315051704.GY21390@mournblade.imrryr.org> <alpine.LFD.2.10.1403171115580.32251@bofh.nohats.ca> <20140317155049.GB24183@mournblade.imrryr.org>
User-Agent: Alpine 2.10 (LFD 1266 2009-07-14)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset="US-ASCII"; format="flowed"
Archived-At: http://mailarchive.ietf.org/arch/msg/dane/9aULsaRq_gkNcIho1WdarErMlvY
Subject: Re: [dane] Digest Algorithm Agility discussion
X-BeenThere: dane@ietf.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: DNS-based Authentication of Named Entities <dane.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/dane>, <mailto:dane-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/dane/>
List-Post: <mailto:dane@ietf.org>
List-Help: <mailto:dane-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/dane>, <mailto:dane-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 17 Mar 2014 16:58:06 -0000
On Mon, 17 Mar 2014, Viktor Dukhovni wrote: >>> * It should be possible for servers to publish TLSA records >>> employing multiple digest algorithms allowing clients to >>> choose the best mutually supported digest. >> >> Isn't that already possible? > > Not based on RFC 6698 alone. With RFC 6698 the client trusts all > TLSA records whether "weak" and "strong". 4.1 states: A TLSA RRSet whose DNSSEC validation state is secure MUST be used as a certificate association for TLS unless a local policy would prohibit the use of the specific certificate association in the secure TLSA RRSet. Can that not be used to reject a weak digest? > My proposal is essentially the same. The client uses the strongest > acceptable digest algorithm. The *client* decides what "strongest" > means. It never chooses an unsupported algorithm. but you want to fail if that one selected one fails. I don't think that is the right decision. >> If a certain digest is so weak it is basically broken, it should not be >> left in a published TLSA record. > > Weak digests (say SHA2-256 if/when broken) cannot be easily removed > from RRsets until all clients support stronger ones. The idea is > to publish stronger digests and deploy stronger clients, then remove > weak digests later. Stronger clients will never use the published > weak records. Otherwise there's an Internet-wide flag-day. I don't think we disagree. the server publishes a new strong digest, and clients that support that and consider sha2-256 weak will not use sha2-256. If the admin messes up the new strong digest, than new clients will fail to get a TLSA record, and old clients will use an unsafe one. >> If the most prefered TLSA record fails validation, the client should try >> another TLSA record. > > This works poorly. While the weak algorithm is being phased out > (years) even clients that support stronger algorithms are at risk. New clients can have a local policy that states never to accept weak digests. I don't see a problem with agility. The weak TLSA records are only left in for clients that support nothing stronger. >> This also gives the server admin some more protection. If they publish >> digests using SHA2-256 and SHA1, and it turns out their tool generates >> bad SHA2-256, than the clients still have a valid SHA1 to fall back to. > > They could also publish a bogus CU or selector, or mess up in many other > ways. I don't think that the intent of multiple algorithms in 6698 is > to mask bogus data. Maybe I don't understand what you think the problem is? >> Perhaps there is text in the DS record RFC to look at that describes >> this better than I just did. > > Perhaps Wes can chime in. His comment to me was that the proposed > DAA (digest algorithm agility) is essentially the only possible > and largely analogous to the DNSSEC approach. So aren't we all agreeing? Paul
- [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Paul Wouters
- Re: [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Paul Hoffman
- Re: [dane] Digest Algorithm Agility discussion Paul Wouters
- Re: [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Paul Hoffman
- Re: [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Paul Wouters
- Re: [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Paul Hoffman
- Re: [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Martin Rex
- Re: [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Mark Andrews
- Re: [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion (c… Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Jim Schaad
- Re: [dane] Digest Algorithm Agility discussion (c… Paul Hoffman
- Re: [dane] Digest Algorithm Agility discussion (c… Andrew Sullivan
- Re: [dane] Digest Algorithm Agility discussion (c… Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion (c… Scott Rose
- Re: [dane] Digest Algorithm Agility discussion (c… Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion (c… Scott Rose
- Re: [dane] Digest Algorithm Agility discussion Wes Hardaker
- Re: [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Peter Palfrader
- Re: [dane] Digest Algorithm Agility discussion Mark Andrews
- Re: [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Mark Andrews
- Re: [dane] Digest Algorithm Agility discussion Peter Palfrader
- Re: [dane] Digest Algorithm Agility discussion Mark Andrews
- Re: [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Peter Palfrader
- Re: [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Mark Andrews
- Re: [dane] Digest Algorithm Agility discussion Mark Andrews
- Re: [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Paul Wouters
- Re: [dane] Digest Algorithm Agility discussion Viktor Dukhovni
- Re: [dane] Digest Algorithm Agility discussion Peter Palfrader
- Re: [dane] Digest Algorithm Agility discussion Wes Hardaker
- Re: [dane] Digest Algorithm Agility discussion Wes Hardaker