Re: Eric Rescorla's Discuss on draft-ietf-httpbis-expect-ct-07: (with DISCUSS and COMMENT)

[Emily Stark <[e-mail]>]

Sorry for the delay. I'm on maternity leave but hope to have these
addressed in the next couple weeks.

On Wed, Nov 21, 2018 at 1:52 PM Eric Rescorla <[e-mail]> wrote:

> Following up, I don't see any response to these comments.
>
> -Ekr
>
>
> On Thu, Sep 13, 2018 at 7:22 AM Eric Rescorla <[e-mail]> wrote:
>
>> I have one other non-blocking comment: Why is this document Experimental?
>> People are already deploying CT without this. It seems like PS would make
>> more sense or Informational.
>>
>> Alexey, I leave it to you.
>> -Ekr
>>
>>
>> On Wed, Sep 12, 2018 at 4:12 PM, Eric Rescorla <[e-mail]> wrote:
>>
>>> Eric Rescorla has entered the following ballot position for
>>> draft-ietf-httpbis-expect-ct-07: Discuss
>>>
>>> When responding, please keep the subject line intact and reply to all
>>> email addresses included in the To and CC lines. (Feel free to cut this
>>> introductory paragraph, however.)
>>>
>>>
>>> Please refer to
>>> https://www.ietf.org/iesg/statement/discuss-criteria.html
>>> for more information about IESG DISCUSS and COMMENT positions.
>>>
>>>
>>> The document, along with other ballot positions, can be found here:
>>> https://datatracker.ietf.org/doc/draft-ietf-httpbis-expect-ct/
>>>
>>>
>>>
>>> ----------------------------------------------------------------------
>>> DISCUSS:
>>> ----------------------------------------------------------------------
>>>
>>> Rich version of this review at:
>>> https://mozphab-ietf.devsvcdev.mozaws.net/D4579
>>>
>>>
>>> This generally seems like a sound mechanism, but I believe there are
>>> some points here that are sufficiently unclear they might create
>>> interop problems,s o I am balloting DISCUSS.
>>>
>>> Most importantly, this document just says you support CT, but that
>>> creates a potential interop problem if say 6962-tris had a different
>>> way of delivering CT information or a different syntax. I'm not saying
>>> you need a version here, but you need to indicate that it's not
>>> forward-looking.
>>>
>>> Also, see below.
>>>
>>> DETAIL
>>> S 2.4.
>>> >      beginning an HTTP conversation over the TLS channel.
>>> >
>>> >      If a connection to a Known Expect-CT Host violates the UA's CT
>>> policy
>>> >      (i.e., the connection is not CT-qualified), and if the Known
>>> Expect-
>>> >      CT Host's Expect-CT metadata indicates an "enforce" configuration,
>>> >      the UA MUST treat the CT compliance failure as an error.
>>>
>>> Is this supposed to be a hard failure, as with HSTS. If not, how does
>>> it interact with HSTS's hard failure reqs.
>>>
>>>
>>> S 3.1.
>>> >         (This may differ from the value of the
>>> "served-certificate-chain"
>>> >         key.)  The value is provided as an array of strings, which MUST
>>> >         appear in the order matching the chain that the UA validated;
>>> each
>>> >         string in the array is the Privacy-Enhanced Mail (PEM)
>>> >         representation of each X.509 certificate as described in
>>> >         [RFC7468].
>>>
>>> What happens if you try to construct multiple paths?
>>>
>>>
>>> S 3.1.
>>> >            does not have or does not trust the public key of the log
>>> from
>>> >            which the SCT was issued), "valid" (indicating that the UA
>>> >            successfully validated the SCT as described in Section 5.2
>>> of
>>> >            [RFC6962] or Section 8.2.3 of
>>> [I-D.ietf-trans-rfc6962-bis]), or
>>> >            "invalid" (indicating that the SCT validation failed because
>>> >            of, e.g., a bad signature).
>>>
>>> Is "invalid" anything other than the specific cases listed above?
>>>
>>>
>>> ----------------------------------------------------------------------
>>> COMMENT:
>>> ----------------------------------------------------------------------
>>>
>>>
>>> >      allows web host operators to instruct user agents to expect valid
>>> >      Signed Certificate Timestamps (SCTs) to be served on connections
>>> to
>>> >      these hosts.  Expect-CT allows web host operators to discover
>>> >      misconfigurations in their Certificate Transparency deployments
>>> and
>>> >      ensure that misissued certificates accepted by UAs are
>>> discoverable
>>> >      in Certificate Transparency logs.
>>>
>>> I don't believe that it does this. Consider a client which simply did
>>> not support CT, then it would (a) accept a misissued certificate that
>>> (b) was not discoverable
>>>
>>>
>>> S 2.1.1.
>>> >
>>> >               Figure 2: Syntax of the report-uri directive value
>>> >
>>> >      "absolute-URI" is defined in Section 4.3 of [RFC3986].
>>> >
>>> >      Hosts may set "report-uri"s that use HTTP or HTTPS.  If the
>>> scheme in
>>>
>>> Why are you allowing HTTP?
>>>
>>>
>>> S 2.3.2.
>>> >         the "enforce", "max-age", or "report-uri" header field value
>>> >         directives convey information different from that already
>>> >         maintained by the UA.  If the "max-age" directive has a value
>>> of
>>> >         0, the UA MUST remove its cached Expect-CT information if the
>>> host
>>> >         was previously noted as a Known Expect-CT Host, and MUST NOT
>>> note
>>> >         this host as a Known Expect-CT Host if it is not already noted.
>>>
>>> As noted above, I think you need to clear the cache when you upgrade
>>> to a potentially incompatible CT version, or otherwise reconfigure the
>>> client.
>>>
>>>
>>> S 2.3.2.1.
>>> >         this host as a Known Expect-CT Host if it is not already noted.
>>> >
>>> >   2.3.2.1.  Noting Expect-CT
>>> >
>>> >      Upon receipt of the Expect-CT response header field over an error-
>>> >      free TLS connection (including the validation adding in Section
>>> 2.4),
>>>
>>> s/adding/added/?
>>>
>>>
>>> S 2.3.2.1.
>>> >      host's domain name and its associated Expect-CT directives in non-
>>> >      volatile storage.
>>> >
>>> >      To note a host as a Known Expect-CT Host, the UA MUST set its
>>> Expect-
>>> >      CT metadata given in the most recently received valid Expect-CT
>>> >      header field, as specified in Section 2.3.2.2.
>>>
>>> This seems ungrammatical. Set it where?
>>>
>>>
>>> S 2.3.2.2.
>>> >
>>> >   2.3.2.2.  Storage Model
>>> >
>>> >      If the substring matching the host production from the Request-URI
>>> >      (of the message to which the host responded) does not congruently
>>> >      match an existing Known Expect-CT Host's domain name, per the
>>>
>>> I would say "exactly match" rather than "congruently match" unless
>>> this ia term of art somewhere.
>>>
>>>
>>> S 2.3.2.2.
>>> >      understands them, the UA MAY note them as well.
>>> >
>>> >      UAs MAY set an upper limit on the value of max-age, so that UAs
>>> that
>>> >      have noted erroneous Expect-CT hosts (whether by accident or due
>>> to
>>> >      attack) have some chance of recovering over time.  If the server
>>> sets
>>> >      a max-age greater than the UA's upper limit, the UA MAY behave as
>>> if
>>>
>>> This MAY seems out of place, given that you already said MAY.
>>>
>>>
>>> S 2.4.
>>> >
>>> >      When a UA connects to a Known Expect-CT Host using a TLS
>>> connection,
>>> >      if the TLS connection has no errors, then the UA will apply an
>>> >      additional correctness check: compliance with a CT Policy.  A UA
>>> >      should evaluate compliance with its CT Policy whenever connecting
>>> to
>>> >      a Known Expect-CT Host, as soon as possible.  However, the check
>>> can
>>>
>>> What does "as soon as possible" mean?
>>>
>>>
>>> S 2.4.
>>> >      terminates the connection due to an Expect-CT failure, this could
>>> >      cause the UA to skip subsequent correctness checks.  When the CT
>>> >      compliance check is skipped or bypassed, Expect-CT reports
>>> >      (Section 3) will not be sent.
>>> >
>>> >      When CT compliance is evaluted for a Known Expect-CT Host, the UA
>>>
>>> Nit: evaluated
>>>
>>>
>>> S 2.4.1.
>>> >      "report-uri" (Section 3).
>>> >
>>> >   2.4.1.  Skipping CT compliance checks
>>> >
>>> >      It is acceptable for a UA to skip CT compliance checks for some
>>> hosts
>>> >      according to local policy.  For example, a UA may disable CT
>>>
>>> Should this be MAY?
>>>
>>>
>>> S 3.1.
>>> >
>>> >      o  "scts": the value represents the SCTs (if any) that the UA
>>> >         received for the Expect-CT host and their validation statuses.
>>> >         The value is provided as an array of JSON objects.  The SCTs
>>> may
>>> >         appear in any order.  Each JSON object in the array has the
>>> >         following keys:
>>>
>>> So these just apply to the EE cert? What about CT for the non-EE
>>> certs?
>>>
>>>
>>>
>>>
>>> S 3.1.
>>> >            of, e.g., a bad signature).
>>> >
>>> >         *  The "source" key, with a string value that indicates from
>>> where
>>> >            the UA obtained the SCT, as defined in Section 3 of
>>> [RFC6962]
>>> >            and Section 6 of [I-D.ietf-trans-rfc6962-bis].  The UA MUST
>>> set
>>> >            the value to one of "tls-extension", "ocsp", or "embedded".
>>>
>>> What do these mean? They seem obvious, but you don't say.
>>>
>>>
>>>
>>