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Re: Proprietary dependencies (was Re: Request for review of the Presentation API from a security perspective)

From: Martin Thomson <martin.thomson@gmail.com>
Date: Tue, 24 Nov 2015 08:57:24 -0800
Message-ID: <CABkgnnVFSj2LRbtYhVpaGV+_fLRuPtTZemjvR3D+6AWK-RhoRg@mail.gmail.com>
To: "Kostiainen, Anssi" <anssi.kostiainen@intel.com>
Cc: François Daoust <fd@w3.org>, WebAppSec WG <public-webappsec@w3.org>, Mike West <mkwst@google.com>, "mark a. foltz" <mfoltz@google.com>
Thanks Anssi,

I'm glad to see that I'm not the only one, and I look forward to
seeing some progress on the CG work.

I don't believe that it is appropriate to call the Presentation API
complete until its prerequisites are stable.  I can imagine some ways
in which the protocol work could be completed without changing the
API, but most of those require some ugly trade-offs.  I'd encourage
you to give the protocol work priority.  I've learned that if you
don't, it's easy to get an non-interoperating mess [1].   And you want
to learn about API changes as early as possible.


[1] Based on what I've seen, that point might have been reached
already. But I'm always willing to be optimistic when starting new

On 24 November 2015 at 05:06, Kostiainen, Anssi
<anssi.kostiainen@intel.com> wrote:
> [ +bcc public-secondscreen ]
> Hi Martin,
> Thanks for your comments. The Second Screen Working Group [1] received similar feedback during the TAG review of the spec. To address TAG's as well as your concern, discussions were started to recharter the Second Screen *Community* Group [2] with the following goals (from the work-in-progress CG charter [3]):
> [[
> Specifically, the CG provides a venue for discussing and incubating early proposals that aim to:
> * define a base set of protocols that Presentation API implementers can refer to to implement the spec;
> * improve interoperability between implementations, i.e. the possibility to associate a presentation controller with a presentation receiver even if they have not been implemented by the same user agent.
> ]]
> Mozilla has provided valuable input to these discussions.
> Thanks,
> -Anssi (Second Screen WG and CG chair)
> [1] http://www.w3.org/2014/secondscreen/
> [2] https://www.w3.org/community/webscreens/
> [3] https://webscreens.github.io/cg-charter/
>> On 23 Nov 2015, at 20:45, Martin Thomson <martin.thomson@gmail.com> wrote:
>> I don't see any mention of any network security aspects of this API.
>> That's worrying.  Not as much from a security perspective - I'm sure a
>> proprietary interface can be implemented to the necessary level of
>> security as much as an open one could.  However, I don't like that
>> this is being developed with a reliance on proprietary technology.
>> The fact that I won't be able to use Browser from vendor X to talk to
>> Screen from vendor Y makes this a technology that could do more harm
>> than good to the open web.
>> Is there any goal of addressing this problem?  It's not like there
>> aren't a good number of options available to us that are
>> well-standardized.  I am aware of the Mozilla implementation and that
>> seems to be relying on RTCPeerConnection for at least part of the
>> underlying technology.
>> On 23 November 2015 at 09:22, Francois Daoust <fd@w3.org> wrote:
>>> Hello WebAppSec WG,
>>> The Second Screen Working Group is working on the Presentation API specification, which enables web content to access external presentation-type displays and use them for presenting web content:
>>>  http://www.w3.org/TR/presentation-api/
>>> The group would like to draw the attention of this group to this working draft and request a security review of the spec. This request was initially sent to the Web Security IG but Mike West suggested we rather got in touch with you.
>>> The group evaluated the spec against the "Self-review questionnaire". See evaluation in:
>>>  https://github.com/w3c/presentation-api/issues/45#issuecomment-100955052
>>> The group has discussed this topic since the evaluation was made and had a lunch discussion with Mike in Sapporo, in particular, mainly around five axes:
>>> 1. Potential issues about the API being inherently cross-origin. There was a feeling that this was acceptable, since there is no way to push information to the other side if it does not want to consume it.
>>> 2. The need to require a secure context in all cases. The feeling here was that the overall risk is relatively low: there is permission involved, the API can do little harm to users. The fingerprinting issue related to the possibility to check whether a second screen is available could be mitigated by preventing it on non-secure contexts.
>>> 3. Mixed content rules for the API: here the group plans to add a requirement to the spec to prevent an existing receiving presentation running in a secure context from receiving input from a controller running in a non secure context.
>>> 4. The behavior of nested frames (i.e. when a nested frame wants to present content as typically needed when one embeds a media player). Mike mentioned an early proposal to delegate permissions to the nested context. In our case, there is no long-term permission and the group is actually considering not requesting any additional iframe attribute à la "allowfullscreen" for a nested frame to be able to call the API.
>>> 5. Security requirements for the messaging channel between secure origins. This touches upon the protocols used under the hoods, which are out of scope of the Second Screen Working Group.
>>> See the summary of this discussion in [1].
>>> Please let us know if you have further comments on these issues, or if you think there are other issues related to the API.
>>> Thanks,
>>> Francois Daoust, Staff Contact
>>> Second Screen Presentation Working Group
>>> [1] http://www.w3.org/2015/10/29-webscreens-minutes.html#item06
Received on Tuesday, 24 November 2015 16:57:53 UTC

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