Hi Ben, The proposal is not to remove the possibility of double signatures, but to relax the requirement so that other use cases become possible.
Our use case is the transition from one dns provider to another without going insecure. If both use the same algorithm you can use the multi-signer dnssec to do this. But if the signers only support a distinct set of algorithms you are out of luck. As Libor pointed out, there are some implications to validation that must be considered. I would say, there are no obvious or easy solutions. But I think/hope that DNSOP will be able to come up with some ideas that we can explore. /Ulrich > On 21 Mar 2022, at 10:32, Ben Schwartz <bem...@google.com> wrote: > > I'm concerned about this. Concretely, this seems like it would raise a major > barrier to rolling out new algorithms. For example, any zone that offers > ECDSA and RSA signatures would be insecure for any RSA-only resolvers. It's > hard to see how new algorithms could be adopted at scale if this rule were in > place. > > On Sun, Mar 20, 2022 at 4:42 PM libor.peltan > <libor.peltan=40nic...@dmarc.ietf.org <mailto:40nic...@dmarc.ietf.org>> wrote: > Hi Ulrich, dnsop, > thank you for your effort in improving DNS. > > This is a follow-up to your proposal on easing the requirements by > RFC4035, which say, in short, that if there's a DS of an algorithm, > there must be a complete DNSKEY set of that algorithm, and if there is a > DNSKEY of an algorithm, the whole zone must be signed by RRSIGs of that > algorithm. > > The counter-proposal is to only require at least one valid > DS-DNSKEY-RRSIG path to sign each RR in the zone. I understand how this > would enable multi-signer setups with the signers supporting different > algorithms, which in turn is beneficial to enable smooth transitions > between such signers. > > Let's suppose we go this way. How do we specify the validator behaviour > when there are algorithm A and B DNSKEYs, just algorithm B RRSIGs, and > the validator only understands algorithm A, but not B? I guess BOGUS > will be no longer proper here, we would probably stick at INSECURE. Am I > correct? > > Now a different scenario. There are algorithm A and B DNSKEYs, the whole > zone is also signed by both alg A and B RRSIGs, and the validator only > understands alg A. Some man-in-the-middle attacker intercepts the > answers by fiddling with the records, while removing algorithm A RRSIGs > from the packets. The validator ends up with INSECURE and lets the > attacker poison some cache... > > With current DNSSEC requirements, it is enough for security if there is > any intersection between the algorithms which the zone is signed by, and > the algorithms supported by the validator, respectively. With your > proposal, it would be required that the validator supports all the > algorithms, which the zone is signed by. > > I agree that in case the zone is signed by just one algorithm > (occasionally being rolled-over to just one different one), these > conditions are equivalent. Fortunately, it did not happen yet (or I'm > not aware of), that the existence of different validators with distinct > sets of supported algorithms forced signers to permanently sign zones > with two algorithms in parallel. The question is, if it remains so for > the future. I can't imagine what would happen in case of a "post-quantum > apocalypse", maybe it wouldn't be a problem, but it might. > > It would also cause the paradox and indeed creepy security quirk, that > if you sign your zone with one more algorithm, which is > cryptographically strong but poorly adopted (perhaps experimental), it > will result in _less_ security. Hardly anyone does this, but if they do, > they will be surprised, I think. > > Just to be clear, I don't want to fight against your ideas. I'm just > pointing at possible problems that could emerge. > > Thanks, > Libor > > _______________________________________________ > DNSOP mailing list > DNSOP@ietf.org <mailto:DNSOP@ietf.org> > https://www.ietf.org/mailman/listinfo/dnsop > <https://www.ietf.org/mailman/listinfo/dnsop>
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