I'm emerging from lurking to just say this: I think this is a fantastic idea, and thank you for doing it. FWIW and IMO, you're better off summarizing the codepoints you are using and planning to use on a wiki somewhere instead of in registries, given the timescales and the lifetime of these codepoints.
- jana On Tue, Jun 12, 2018 at 9:28 AM David Benjamin <david...@chromium.org> wrote: > Hi all, > > Now that TLS 1.3 is about done, perhaps it is time to reflect on the > ossification problems. > > TLS is an extensible protocol. TLS 1.3 is backwards-compatible and may be > incrementally rolled out in an existing compliant TLS 1.2 deployment. Yet > we had problems. Widespread non-compliant servers broke on the TLS 1.3 > ClientHello, so versioning moved to supported_versions. Widespread > non-compliant middleboxes attempted to parse someone else’s ServerHellos, > so the protocol was further hacked to weave through their many defects. > > I think I can speak for the working group that we do not want to repeat > this adventure again. In general, I think the response to ossification is > two-fold: > > 1. It’s already happened, so how do we progress today? > 2. How do we avoid more of this tomorrow? > > The workarounds only answer the first question. For the second, TLS 1.3 > has a section which spells out a few protocol invariants > <https://tlswg.github.io/tls13-spec/draft-ietf-tls-tls13.html#rfc.section..9.3>. > It is all corollaries of existing TLS specification text, but hopefully > documenting it explicitly will help. But experience has shown specification > text is only necessary, not sufficient. > > For extensibility problems in servers, we have GREASE > <https://tools.ietf.org/html/draft-ietf-tls-grease-01>. This enforces the > key rule in ClientHello processing: ignore unrecognized parameters. GREASE > enforces this by filling the ecosystem with them. TLS 1.3’s middlebox woes > were different. The key rule is: if you did not produce a ClientHello, you > cannot assume that you can parse the response. Analogously, we should fill > the ecosystem with such responses. We have an idea, but it is more involved > than GREASE, so we are very interested in the TLS community’s feedback. > > In short, we plan to regularly mint new TLS versions (and likely other > sensitive parameters such as extensions), roughly every six weeks matching > Chrome’s release cycle. Chrome, Google servers, and any other deployment > that wishes to participate, would support two (or more) versions of TLS > 1.3: the standard stable 0x0304, and a rolling alternate version. Every six > weeks, we would randomly pick a new code point. These versions will > otherwise be identical to TLS 1.3, save maybe minor details to separate > keys and exercise allowed syntax changes. The goal is to pave the way for > future versions of TLS by simulating them (“draft negative one”). > > Of course, this scheme has some risk. It grabs code points everywhere. > Code points are plentiful, but we do sometimes have collisions (e.g. 26 and > 40). The entire point is to serve and maintain TLS’s extensibility, so we > certainly do not wish to hamper it! Thus we have some safeguards in mind: > > * We will document every code point we use and what it refers to. (If the > volume is fine, we can email them to the list each time.) New allocations > can always avoid the lost numbers. At a rate of one every 6 weeks, it will > take over 7,000 years to exhaust everything. > > * We will avoid picking numbers that the IETF is likely to allocate, to > reduce the chance of collision. Rolling versions will not start with 0x03, > rolling cipher suites or extensions will not be contiguous with existing > blocks, etc. > > * BoringSSL will not enable this by default. We will only enable it where > we can shut it back off. On our servers, we of course regularly deploy > changes. Chrome is also regularly updated and, moreover, we will gate it on > our server-controlled field trials > <https://textslashplain.com/2017/10/18/chrome-field-trials/> mechanism. > We hope that, in practice, only the last several code points will be in use > at a time. > > * Our clients would only support the most recent set of rolling > parameters, and our servers the last handful. As each value will be > short-lived, the ecosystem is unlikely to rely on them as de facto > standards. Conversely, like other extensions, implementations without them > will still interoperate fine. We would never offer a rolling parameter > without the corresponding stable one. > > * If this ultimately does not work, we can stop at any time and only have > wasted a small portion of code points. > > * Finally, if the working group is open to it, these values could be > summarized in regular documents to reserve them, so that they are > ultimately reflected in the registries. A new document every six weeks is > probably impractical, but we can batch them up. > > We are interested in the community’s feedback on this proposal—anyone who > might participate, better safeguards, or thoughts on the mechanism as a > whole. We hope it will help the working group evolve its protocols more > smoothly in the future. > > David > _______________________________________________ > TLS mailing list > TLS@ietf.org > https://www.ietf.org/mailman/listinfo/tls >
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