Re: [expect-ct] Is expect-ct policy intended for long-term use? (plus: no user recourse)
Tom Ritter <tom@ritter.vg> Sat, 26 November 2016 03:43 UTC
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From: Tom Ritter <tom@ritter.vg>
Date: Fri, 25 Nov 2016 21:38:17 -0600
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To: =JeffH <Jeff.Hodges@kingsmountain.com>
Cc: Emily Stark <estark@google.com>, IETF HTTP WG <ietf-http-wg@w3.org>
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Subject: Re: [expect-ct] Is expect-ct policy intended for long-term use? (plus: no user recourse)
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Expect-CT has usefulness long-term if a browser chooses not to require CT for all certs, but implements the spec anyway. A browser could implement Expect-CT by making a minimal policy (perhaps by choosing to select an intersection of logs trusted by other browsers), and simply verifying SCT signatures. -tom On 24 November 2016 at 20:00, =JeffH <Jeff.Hodges@kingsmountain.com> wrote: > Emily wrote: >> I anticipate Expect-CT to be useful more than a year and less than 5 >> years. Within 1-2 years, I expect/hope several browsers will be >> requiring CT for all new certificates. They can still implement >> Expect-CT to protect sites against backdating and against >> certificates that were issued before the date that they started >> requiring CT for all new certs. > > ok, by "they" you mean UAs, yes? > > >> Once a browser is requiring CT for *all* certificates (e.g. because >> the maximum validity period has elapsed beyond the date that the >> browser began requiring CT for all new certs), then I don't think >> Expect-CT is useful for that browser anymore. > > by implication you mean "useful" for a server (aka "relying party" (RP)) and > user, yes? > > because what we are protecting here is not so much the browser (vendor) but > the RP and user, yes? > > I could see Expect-CT to be useful for the longer term if it were to signal > additional RP-desired selective UA behavior such as "no user recourse", *if* > the browsers were not going to implement such behavior, e.g., as a a matter > of course in the case of errors during secure connection establishment. > > =JeffH > > > >> On Wed, Nov 23, 2016 at 4:47 PM, =JeffH >> <Jeff.Hodges@kingsmountain.com> wrote: >> WRT "Expect-CT" >> <https://tools.ietf.org/html/draft-stark-expect-ct> >> (aka "the I-D" in the below)... >> >> Is the expect-ct policy intended to be used long-term by servers? >> >> I.e., is this server-declared expect-ct policy only a stop-gap until >> all browsers natively enforce their vendors' "ct policies"? >> >> At first glance, it seems the answer is "yes, expect-ct has long-term >> usefulness" given the language in >> <https://tools.ietf.org/html/draft-stark-expect-ct-00#section-2.1.2>, >> >> i.e., a host's declaration of expect-ct policy is stating that the UA >> must terminate any connection to that host (and port?) that does not >> satisfy the UA's ct policy. >> >> However, given this.. >> >> On Sunday, November 13, 2016 at 4:47 AM, Emily Stark wrote: >>> That is, eventually, when browsers require CT for all >>> certificates, [...] 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) >> >> ..it sounds like the browsers intend to do that in any case, and if >> so, on what timescale? >> >> I.e., is it worthwhile to go through all the work to formally define >> Expect-CT in an RFC? >> >> I'm not sure. This is part of the reason why I uploaded this as an >> experimental draft. I'm not 100% sure what's the right process or >> venue is for a mechanism that is not meant to stick around forever. >> >> >> Though, if there is some functionality that a server-declared >> expect-ct policy stipulates that is not intended to be implemented by >> default in near- to intermediate-term, then formally specifying >> Expect-CT perhaps has a reasonable cost-benefit regardless. Or also >> if explicit server-declared "expect-ct" policy would be useful to the >> long-tail of HTTPS clients other than the dominant browsers. >> >> Perhaps one should consider having the expect-ct policy additionally >> mean that there is "no user recourse" to connection termination as a >> result of CT-policy violation. I note the I-D does not presently >> state that. >> >> See <https://tools.ietf.org/html/rfc6797#section-12.1> for how this >> is discussed in HSTS. You might consider adding "no user recourse" to >> a "UA implementation advice" section. >> >> That seems reasonable to include, though I don't think "no user >> recourse" is enough benefit to justify keeping Expect-CT around after >> it has otherwise exhausted its usefulness. >> >> >> Though, like any of this (including HSTS), the browsers could in the >> future decide that they will have a "no user recourse" policy by >> default for all secure transport establishment failures. It's a >> question of how far in the future might that occur (in order to >> justify present-to-intermediate-term work). >> >> HTH, >> >> =JeffH >> >> >> > >
- [expect-ct] Is expect-ct policy intended for long… =JeffH
- Re: [expect-ct] Is expect-ct policy intended for … Emily Stark
- [expect-ct] Is expect-ct policy intended for long… =JeffH
- Re: [expect-ct] Is expect-ct policy intended for … Tom Ritter
- Re: [expect-ct] Is expect-ct policy intended for … Emily Stark