Re: [EME] Key Release

On Tue, Jun 19, 2012 at 8:52 AM, Mark Watson <watsonm@netflix.com> wrote:

>
>  On Jun 11, 2012, at 11:57 PM, David Dorwin wrote:
>
> https://www.w3.org/Bugs/Public/show_bug.cgi?id=17199
>
>  The Key Release portion (
> http://dvcs.w3.org/hg/html-media/raw-file/tip/encrypted-media/encrypted-media.html#key-release)
> of the proposal hasn't received a lot of feedback, so I'd like to start a
> discussion about it.
>
>  Section 4.1 gives a good overview of the problem. Briefly, the goal is
> the provide the application with secure proof that a key is no longer
> present on the client ("released"). The application must also be able to
> ACK proofs. One particular thing to note is that proofs are not related
> to any particular media element. In addition, the current API proposal does
> not associate key release with HTMLMediaElement or any other object.
>
>  Some possible topics for discussion:
>  * Multiple KeyReleaseManagers could be created, but they would all
> represent the same data. How might we make KeyReleaseManager global or a
> singleton?
>
>
>  I would like to better understand what is the "normal" way to do this ?
> Should this be window.mediakeyreleasemanager ? What are the issues with
> that ?
>
>   * While not related to HTMLMediaElement from an API point of view, key
> release would need to be tightly integrated with the implementation
> underlying the rest of the proposal, which is related to HTMLMediaElement.
>    - What is the impact on implementations?
>    - How might we more closely associate key release with HTMLMediaElement
> and/or the rest of the EME implementation?
>
>
>  If it makes a significant difference for implementations then this could
> be dealt with using methods on HTMLMediaElement, with the consequence that
> you might need to create a "dummy" HTMLMediaElement to get access to the
> proof of key release messages.
>

I think this is worth investigating. One thing we will have to address is
ensuring that the media element implementation can be sufficiently
initialized in the "dummy" case. See
https://www.w3.org/Bugs/Public/show_bug.cgi?id=17470, which is tracking
when we applications call other methods, specifically generateKeyRequest().

>
>   * How might representing sessions as objects (
> https://www.w3.org/Bugs/Public/show_bug.cgi?id=16613) affect the design?
>
>
>  I think it makes it clearer, since the "proof of key release" messages
> are created (and stored in the CDM) exactly when a  "session" is destroyed.
> In fact they become "proof of session destruction" instead.
>
>  …Mark
>
>