Re: Genart last call review of draft-ietf-httpbis-client-hints-13

Addressed the latest points in the PR. Thanks! :)

On Wed, May 6, 2020 at 3:20 PM Yoav Weiss <yoav@yoav.ws> wrote:

>
>
> On Wed, May 6, 2020 at 2:43 PM Christer Holmberg <
> christer.holmberg@ericsson.com> wrote:
>
>> Hi Yoav,
>>
>> >> I have not received the pull request yet, so I will comment only based
>> on your e-mail reply :)
>> >
>> > Apologies for the delay. PR is now up at
>> https://protect2.fireeye.com/v1/url?k=0a42e34e-54e25920-0a42a3d5-
>> >
>> 869a14f4b08c-11c3f32cbd74f2f2&q=1&e=978d85da-fab3-4523-a8d9-447aa6bdf056&u=
>> https://github.com/httpwg/http-extensions/pull/1171
>>
>> Thanks!
>>
>> I think it looks ok.
>>
>> BTW, are high-entropy and low-entropy defined and well-known HTTP terms?
>>
>
> I'm not sure. The browser processing model defines a list of low-entropy
> CH headers:
> https://wicg.github.io/client-hints-infrastructure/#low-entropy-table
> I could point at that.
>
>
>> ---
>>
>> MaQ3:
>>
>> >>>> Related to MaQ2, what happens if a server receives hints that it
>> does not
>> >>>> understand, or does not support?
>> >>>
>> >>> Servers SHOULD ignore hints they do not understand or do not support.
>> >>
>> >> Is there are reason for not using MUST? SHOULD typically means
>> MUST-unless-X. What would X be?
>> >>
>> >> Is there a way for the server to indicate to the client that it did
>> not understand/support the hints? Whatever the answer, I think it would be
>> good to have some text about that.
>> >
>> > There's no such a mechanism, similar to other request headers.
>> > Do you have sample text in mind that may make that point clearer?
>>
>> Maybe just a note pointing out that there is no mechanism for a server to
>> inform a client whether it understands and supports the hints.
>>
>> ---
>>
>> Minor issues:
>>
>> MiQ1:
>>
>> >>> Section 1 described that proactive content negotiation allows servers
>> to
>> >>> silently fingerprint the user agent.
>> >>>
>> >>> But, later in the Section it is described that Client Hints also
>> allow a server
>> >>> the perform fingerprinting, and the Security Considerations also say
>> that there
>> >>> is really no difference.
>> >>>
>> >>> So, does Section 1 need to talk about fingerprinting at all?
>> >>
>> >> Section 1 describes the fact that traditional (read: pre-Client Hints)
>> content negotiation methods relied on sending information to all servers,
>> which enabled passive fingerprinting,
>> >> and how Client Hints breaks away from that paradigm, by only sending
>> (high entropy) hints when the server needs them and opts-in to receive them.
>> >>
>> >> A server can request the hints even if it doesn't "need" them, but it
>> wants to do fingerprinting. The client does not know what the server will
>> do with the information.
>> >>
>> >> My point is that the reader should not get an impression that client
>> hints somehow prevents fingerprinting. It doesn't. The only difference is
>> that the server has to ask for the information.
>> >
>> > Current draft includes " Client Hints mitigate ... privacy concerns of
>> passive fingerprinting by requiring explicit opt-in and disclosure of
>> > required headers by the server through the use of the Accept-CH
>> response header."
>> > Should that be clearer?
>>
>> Yes, I think it is better.
>>
>> -------
>>
>> Regards,
>>
>> Christer
>>
>>