Re: [Acme] ACME breaking change: Most GETs become POSTs

[Richard Barnes <[e-mail]>]

After the weekend's discussions, I've updated the PR to reflect what I
understand to be emerging agreement on these topics:

ISSUE 1. Should we do POST-as-GET at all, vs. keeping GET and doing the
privacy analysis?
PROPOSED RESOLUTION: Yes.

ISSUE 2: How should we signal that POST-as-GET request is different from
other POST requests?
PROPOSED RESOLUTION: A JWS with a zero-octet payload ("")

ISSUE 3: Should servers be required to allow GET requests for certificate
URLs?
PROPOSED RESOLUTION: No, but they MAY

ISSUE 4: How should we address the risk that an attacker can discover URLs
by probing for Unauthorized vs. Not Found?
PROPOSED RESOLUTION: Security considerations that recommend
non-correlatable URL plans

https://github.com/ietf-wg-acme/acme/pull/445

Adam: Is this looking like an approach that would satisfy your DISCUSS?

Chairs / EKR: How would you like to proceed on closing this out?  What are
the next process steps?


On Fri, Aug 31, 2018 at 6:08 PM Richard Barnes <[e-mail]> wrote:

> Hey all,
>
> This thread forked into a couple of different issues, so I wanted to post
> a little end-of-day summary of the issues and where we stand.  I've updated
> the PR [1] to reflect most of today's discussion.
>
> ===
>
> ISSUE 1. Should we do POST-as-GET at all, vs. keeping GET and doing the
> privacy analysis?
>
> It seems like there's pretty strong agreement that we should get rid of
> GET, as the architecturally cleanest option.
>
> ===
>
> ISSUE 2: How should we signal that POST-as-GET request is different from
> other POST requests?
>
> The current PR signals this by sending a JWS with an empty (zero-octet)
> payload, instead of a JSON object.  Jacob and Daniel suggested that we
> should instead use the payload being an empty JSON object as the signal.
> An earlier draft PR used a field in the protected header.
>
> ===
>
> ISSUE 3: Should servers be required to allow GET requests for certificate
> URLs?
>
> I had proposed this earlier today; Jacob and Daniel pushed back.  I have
> implemented a compromise in the latest PR, where servers MAY accept GET
> requests.
>
> ===
>
> ISSUE 4: How should we address the risk that an attacker can discover URLs
> by probing for Unauthorized vs. Not Found?
>
> There seemed to be agreement on the list that this should be addressed
> with some guidance to servers on how to assign URLs.  I have just added
> some text to the PR for this.
>
> ===
>
> It seems to me we're pretty much closed on the first issue, and the other
> three are still open.  Please send comments, so we can resolve this issue
> and get the document back in motion!
>
> Thanks,
> --Richard
>
> [1] https://github.com/ietf-wg-acme/acme/pull/445
>
> On Thu, Aug 30, 2018 at 7:20 PM Jacob Hoffman-Andrews <[e-mail]>
> wrote:
>
>> ACME currently has unauthenticated GETs for some resources. This was
>> originally discussed in January 2015[1]. We decided to put all sensitive
>> data in the account resource and consider all GET resources public, with
>> a slant towards transparency.
>>
>> Adam Roach recently pointed out in his Area Director review that even
>> when the contents of GET URLs aren’t sensitive, their correlation may
>> be. For instance, some CAs might consider the grouping of certificates
>> by account to be sensitive.
>>
>> Richard Barnes proposes[2] to change all GETs to POSTs (except directory
>> and new-nonce). This will be a breaking change. Clients that were
>> compatible with previous drafts, informally called ACMEv1 and ACMEv2,
>> will not be compatible with a draft that mandates POSTs everywhere. It
>> will be a painful change, since the ecosystem just started switching to
>> ACMEv2, which looked to be near-final.
>>
>> I think this is the right path forwards. ACME will be a simpler, better
>> protocol long-term if all requests are authenticated. However, if we’re
>> taking this path we should aim to come to consensus and land the final
>> spec quickly to reduce uncertainty for ACME client implementers.
>>
>> [1]
>> https://github.com/letsencrypt/acme-spec/pull/48#issuecomment-70169712
>> [2] https://github.com/ietf-wg-acme/acme/pull/445/files
>>
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>