On Thu, Mar 24, 2022 at 9:53 AM Ulrich Wisser <ulrich= 40wisser...@dmarc.ietf.org> wrote:
> Hi Mark, > > Sorry for the late answer, IETF and some other stuff keeps me busy. > > > Let’s start with this > > *We did not and do not propose to remove anything from RFC 4035. Currently > we are asking for RFC 6840 to be amended * > > *RFC 6840 Se*ction 5.11 > > This requirement applies to servers, not validators. Validators > SHOULD accept any single valid path. They SHOULD NOT insist that all > algorithms signaled in the DS RRset work, and they MUST NOT insist > that all algorithms signaled in the DNSKEY RRset work. > > > PROPOSED CHANGE > > This requirement applies to servers, not validators. Validators > SHOULD accept any single valid path. They *MUST* NOT insist that all > algorithms signaled in the DS RRset work, and they MUST NOT insist > that all algorithms signaled in the DNSKEY RRset work. > > > > We absolutely do not want to enable lying. We want to enable transfer of > domains between to signers using different algorithms. > > I share your analysis that this is possible today. It violates RFC 4035 > section 2.2. It should work given that you use two fairly well supported > algorithms and your resolver follows the “SHOULD” in RFC 6840 section 5.11. > > So the first step is to change 6840 to “MUST”, so that resolvers use any > validation path and do not insist on a specific or all algorithms being > present. > > Secondly, problems arise if a resolver only supports one of the > algorithms. In that case half of the answers would be considered bogus. We > are looking for a way to make this work. > > I admit, the problem is not trivial, but I have faith in DNSOP! ( Please > don’t prove me wrong. Pretty please!) > So, just to recap the problem(s) for which a solution is desired, and also the implications/dependencies of various solutions to the problem(s): - Migrate a signed delegation from provider X using algorithm A only to provider Y using algorithm B only - Validators that support both A and B must always have validation result "secure" during the migration (before/during/after) - Validators that support only A or only B must always have validation result of "secure" or "insecure", never "bogus" - There may be (are?) validators deployed which, if they understand two algorithms (call them C and D, which may or may not be A and/or B respectively) require that if two DS exists (C and D), that the DNSKEY RRSET be signed by both C and D (signed == with SEP bit set) Starting with the simplest corner case: - A validator that supports A but does not support B, will treat a DS RRSET which has both A and B, as if the B records do not exist, and thus the DS RRSET only contains A record(s). This means that if alg A DS record exists, the DNSKEY set MUST be signed with alg A. - Ditto for B - This results in a requirement that if two alg DS records exist (A and B), the DNSKEY set must be signed by both. - Changing the requirement on how a validator that supports both (A and B) does not remove this requirement, unfortunately. This is a different corner case than the one for one algorithm, but two provider's DS records, where each provider's version of the zone has one KSK (their own) and two ZSKs (theirs and the other provider's). In that situation, the DNSKEY set is validated by either KSK (which has a matching DS), and enables both ZSKs (only one of which will actually sign each provider's records), permitting validation of records of a mix/match record+RRSIG in a cache. I do have a solution which allows each provider to have exclusive control of their respective private keys. It does not, however, involve both providers both being "active" at any point in time. I think this is the only viable mechanism, without having to go back to the design phase of DNSSEC, unfortunately: - Start with provider X using algorithm A - Add provider Z also using algorithm A. The provider Z MUST support both A and B algorithms. (This might actually be the zone owner, or could be a third provider.) - Do the usual thing with each provider having their own KSK, and both ZSKs. Publish both DS records (one for each provider's KSK). - Remove provider X, unpublish X's DS, remove X's ZSKs (in the normal order of operations needed to not go insecure and not go bogus) - Have provider Z do an algorithm roll from A to B. Z can do this unilaterally, since Z would have private keys for both KSKs (one each of algorithm A and B) - Provider Z is now only publishing with algorithm B - Add provider Y using algorithm B (Y and Z both using algorithm B, normal single algorithm dual signer) - Remove provider Z - Profit It should always be possible to find someone who can temporarily operate a zone, who supports the two algorithms of the respective before and after providers. At worst, this could involve self-hosting (possibly with use of added providers who support zone transfer of signed zones to improve availability and/or avoid serving the zone on the signing server, i.e. using "hidden primary" method. Brian > > /Ulrich > > > > > On 22 Mar 2022, at 00:59, Mark Andrews <ma...@isc.org> wrote: > > Also the whole point of mandatory to implement (which includes business > practices) is to prevent cases like this. > If a business wants to lie to its customers about supporting DNSSEC it > should be taken to court, preferably by > bodies like the ACCC. > > As for migration between providers, provided there is some co-operation, > it is possible to migrate between two providers with non overlapping > algorithms. It does require the signed zone data to be transferred back and > forth between the operators. It does require DNSKEY records to be swapped. > > raw zone + provider B keys -> add A keys and sign by A -> sign by B > preserving A signatures and keys -> transfer to A for serving. > > This works today and requires no DNSSEC protocol changes. It may require > some minor implementation changes. For BIND that would be to stop > stripping out DNSSEC stuff from A at B when inline signing. It could all > be done in single server instances with views. This is conceptually what > BIND does when introducing a new algorithm with incremental signing except > for transferring the new zone back and forth. > > On 22 Mar 2022, at 06:58, Ben Schwartz <bemasc=40google....@dmarc.ietf.org> > wrote: > > If we assume the existing install base of resolvers isn't going away, then > I don't see how we could relax the requirement. There are already deployed > resolvers enforcing it. You would need a "flag day" to deprecate them, > which could not happen for many years. > > This seems a lot harder than just telling your next DNS provider that you > can't do business with them until they implement another one of the (very > small number of) widely implemented algorithms. > > Of course, I've personally argued for essentially the opposite of this > proposal [1]. Until DNSSEC has algorithmic agility without sacrificing > compatibility or security, it's only usable as "extra" security. > > [1] > https://www.ietf.org/archive/id/draft-schwartz-dnsop-dnssec-strict-mode-00.html > > On Mon, Mar 21, 2022 at 12:06 PM Ulrich Wisser <ulr...@wisser.se> wrote: > 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> 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 > https://www.ietf.org/mailman/listinfo/dnsop > > > _______________________________________________ > DNSOP mailing list > DNSOP@ietf.org > https://www.ietf.org/mailman/listinfo/dnsop > > > -- > Mark Andrews, ISC > 1 Seymour St., Dundas Valley, NSW 2117, Australia > PHONE: +61 2 9871 4742 INTERNET: ma...@isc.org > > > _______________________________________________ > DNSOP mailing list > DNSOP@ietf.org > https://www.ietf.org/mailman/listinfo/dnsop >
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