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

[ +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.


-Anssi (Second Screen WG and CG chair)




> On 23 Nov 2015, at 20:45, Martin Thomson <> 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 <> 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:

>> 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:

>> 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]


Received on Tuesday, 24 November 2015 13:07:08 UTC