Re: Comments on draft-stark-expect-ct-00
Emily Stark <estark@google.com> Fri, 02 December 2016 17:24 UTC
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From: Emily Stark <estark@google.com>
Date: Fri, 02 Dec 2016 09:18:57 -0800
Message-ID: <CAPP_2SYCbYMqRkFf9Z7LfwViQytgqngm6wzjnADH8U-tVbTo9w@mail.gmail.com>
To: Nick Sullivan <nicholas.sullivan@gmail.com>
Cc: Eric Rescorla <ekr@rtfm.com>, HTTP Working Group <ietf-http-wg@w3.org>
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Subject: Re: Comments on draft-stark-expect-ct-00
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Just a note that I've uploaded a new version which caches report-only headers based on the feedback here: https://datatracker.ietf.org/doc/draft-stark-expect-ct/ On Mon, Nov 28, 2016 at 3:54 PM, Nick Sullivan <nicholas.sullivan@gmail.com> wrote: > Cloudflare is considering using this header in report-only mode to help > identify issues in our CT-stapling infrastructure. This data will help us > with future CT decisions. > > We would naturally expect report-only and enforce mode to have the same > semantics, which includes caching. Although our CT-stapling and > header-adding infrastructures are de-coupled, there is a use case for > caching report-only headers: load balancing. Our connections are load > balanced, so subsequent connections may not end up on the same server as > the previous connection. Cached enforcement headers would help us catch > issues where both the CT-stapling configuration and the header-adding > configuration failed to run on a server. With caching, it's more likely > that a > that server with a broken CT config will end up handling resumed > connection from a user agent that had previously connected to a > properly-configured server that that had set the header. > > Nick > > On Fri, Nov 25, 2016 at 11:21 AM Eric Rescorla <ekr@rtfm.com> wrote: > >> On Mon, Nov 21, 2016 at 3:28 PM, Emily Stark <estark@google.com> wrote: >> >> Summarizing some hallway conversations from IETF: >> >> - Caching in report-only mode: I can be convinced that this is useful, >> in case where you are e.g. rolling out a CT-compliant certificate in >> conjunction with Expect-CT (for example if you have a config that >> turns on CT and also turns on Expect-CT in report-only mode, and the >> config didn't make it out to a few of your servers). Will be >> especially convinced if site owners say that this is how they want it >> to work. >> >> >> I'd in general be interested in hearing from site owners on how they >> feel about this header. That would be a good addition to this discussion. >> >> >> - Policy: One can draw an analogy to HSTS, where a site promises to >> provide a certificate that is valid according to the client's >> definition of valid, including factors that vary across clients >> (variations in trust stores, SHA1 deprecation, etc.). In practice, I >> don't think CT will be more of a foot-gun than HSTS (and certainly >> much less than HPKP) because browsers are in close collaboration to >> work out policies that play nicely with each other. >> >> >> I'm not sure how strong the analogy is here. It's actually a nontrivial >> inconvenience >> for sites that different browsers have different policies. With that >> said, it's not something >> I'm willing to make a big deal of if the send of the WG is otherwise. >> >> -Ekr >> >> >> >> On Mon, Nov 14, 2016 at 8:53 PM, Eric Rescorla <ekr@rtfm.com> wrote: >> > On Tue, Nov 15, 2016 at 10:50 AM, Emily Stark <estark@google.com> >> wrote: >> >> >> >> >> >> >> >> >> >> (https://groups.google.com/d/msg/mozilla.dev.security. >> policy/VJYX1Wnnhiw/ZaJBaKfKBQAJ). >> >> >> That is, eventually, when browsers require CT for all certificates, >> >> >> site owners will have to face this same problem of making sure that >> >> >> all their certificate chains are compliant with the CT policies of >> all >> >> >> the UAs that they care about. So I guess I see the interop problem >> as >> >> >> somewhat separate, perhaps something that should be addressed on its >> >> >> own when the CT ecosystem and implementations have matured enough >> that >> >> >> UAs are able to standardize on one policy...? >> >> >> >> >> >> To put it another way, I see Expect-CT as a way that individual >> sites >> >> >> can opt in to the future early ("the future" being when browsers >> >> >> require CT for all certificates), and the future is quite possibly >> >> >> different policies in different browsers, at least for some amount >> of >> >> >> time. >> >> > >> >> > >> >> > The problem is that as written the future is likely to involve a lot >> of >> >> > bustage. >> >> >> >> I feel like maybe I'm not understanding what you'd like to see >> >> instead. Are you arguing that the Expect-CT draft should contain a >> >> policy like "all EE certs must come with 2 SCTs from different logs", >> >> even if that policy differs from what different browsers plan to >> >> actually enforce for new certificates? Or that browsers shouldn't >> >> require CT for all certificates until they standardize on such a >> >> policy? >> > >> > >> > I'm arguing that we shouldn't define a header that says "you must >> enforce >> > CT" >> > without defining what "enforce CT" means. >> > >> > -Ekr >> > >> >> >> >> > >> >> > >> >> >> > S 2.1.3. >> >> >> > What's the rationale for not caching the directive in report-only >> >> >> > mode. >> >> >> > If the purpose of the report-only mode is to tell you when you >> have >> >> >> > nonconforming servers, then don't you want to be able to turn it >> on >> >> >> > on server A and detect hwen server B is broken? That seems like it >> >> >> > doesn't work if you don't cache. >> >> >> >> >> >> I'm tempted to say "because that's how HPKP does it", but that's >> >> >> probably not the answer you're looking for. :) I'd expect that sites >> >> >> would generally serve the report-only header on all responses >> >> >> unconditionally. I can't really think of a common misconfiguration >> >> >> scenario that would cause a CT violation and would *also* cause the >> >> >> header to not be served, but maybe that's a failure of imagination >> on >> >> >> my part. >> >> > >> >> > >> >> > Two different independent servers with the same name behind >> >> > a load balancer? Or a server farm where policies are rolled out >> slowly. >> >> > >> >> > -Ekr >> >> > >> >> >> >> >> >> >> >> >> > >> >> >> > -Ekr >> >> >> >> >> > >> > >> > >> >>
- Comments on draft-stark-expect-ct-00 Eric Rescorla
- Re: Comments on draft-stark-expect-ct-00 Tom Ritter
- Re: Comments on draft-stark-expect-ct-00 Emily Stark
- Re: Comments on draft-stark-expect-ct-00 Tom Ritter
- Re: Comments on draft-stark-expect-ct-00 Emily Stark
- Re: Comments on draft-stark-expect-ct-00 Eric Rescorla
- Re: Comments on draft-stark-expect-ct-00 Emily Stark
- Re: Comments on draft-stark-expect-ct-00 Eric Rescorla
- Re: Comments on draft-stark-expect-ct-00 Emily Stark
- Re: Comments on draft-stark-expect-ct-00 Eric Rescorla
- Re: Comments on draft-stark-expect-ct-00 Nick Sullivan
- Re: Comments on draft-stark-expect-ct-00 Emily Stark