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Re: Bug 25269

From: Mark Watson <watsonm@netflix.com>
Date: Fri, 6 Jun 2014 16:47:23 -0700
Message-ID: <CAEnTvdCy9-fFpUE4t-G+KZvHQv3Zk+j0RQWEre-JAcAw-q-tfg@mail.gmail.com>
To: Joe Steele <steele@adobe.com>
Cc: David Dorwin <ddorwin@google.com>, "<public-html-media@w3.org>" <public-html-media@w3.org>
Key Ids are generally random 16-byte identifiers. I don't think we can
assume that a title id can be derived from a key id except by a database
lookup.

...Mark


On Fri, Jun 6, 2014 at 4:39 PM, Joe Steele <steele@adobe.com> wrote:

> You are right — as a random 16-byte value it *should* be unique. However
> the CENC spec does not seem to say that *must* be the case. Thus my
> concern.
>
> I am looking at this text (emphasis mine) from ISO/IEC CD 23001-7 2nd
> Edition:
> "NOTE: For global uniqueness, a UUID [1] *should *be used for each unique
> KID /key value pair to prevent
> duplicate IDs for different keys by independent publishers. Publishers may
> use the same key value and
> KID  in more than one track or file according to their rights management
> intentions."
>
> Option #2 only works if the keys are unique for all titles as you point
> out. This is a catch-22. My assumption is that they are not unique.
> Option #3 is a non-starter because the CDM needs to be able to attest to
> the information in the license request and it can’t unless it has all of it.
>
> I suggest we add a note in the spec that emphasizes that these must be
> unique and suggests Option #1 as a good way to do it.
> That seems like minimal effort. If implementers run into this problem it
> will point them in the right direction even if they can’t make the
> suggested change.
>
> Joe
>
> On Jun 4, 2014, at 10:47 AM, David Dorwin <ddorwin@google.com> wrote:
>
> Yes, it is just an array of key IDs.
>
> There are a few options to identify the title:
>
>    - The key ID(s) could include the title ID in them, allowing it to be
>    easily extracted on the server. (This forces unique key IDs.)
>    - The server can look the title up based on the key ID(s). (This
>    assumes they are unique.)
>    - The application knows the title and can include this in its request.
>
>
>  Why do you say KID isn't generally unique across streams? That should
> probably be a best practice for content providers.
>
> David
>
>
> On Tue, Jun 3, 2014 at 10:42 AM, Joe Steele <steele@adobe.com> wrote:
>
>> https://www.w3.org/Bugs/Public/show_bug.cgi?id=25269
>>
>> This bug was closed on Saturday. Rather than just re-open it — maybe you
>> can give me some clarification.
>>
>> Your proposal only includes the KIDs in the data that is sent into the
>> CDM — correct?
>>
>> Given that KID is not generally unique across streams, how are you
>> planning to support this? I would expect implementations to require a title
>> identifier to pass to the server in order to identify the title that the
>> KID is associated with. It sounds like you are proposing that the
>> application which has this information should send it to the server in some
>> out of band communication.
>>
>> Joe
>>
>
>
>
Received on Friday, 6 June 2014 23:47:51 UTC

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