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[Bug 19788] What, if any, event should be fired when no key is available to decrypt the block?

From: <bugzilla@jessica.w3.org>
Date: Tue, 30 Oct 2012 22:34:53 +0000
To: public-html-bugzilla@w3.org
Message-ID: <bug-19788-2486-gX2lYftboj@http.www.w3.org/Bugs/Public/>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=19788

--- Comment #2 from David Dorwin <ddorwin@google.com> ---
Follow-up: Should the event for the Encrypted Block Encountered algorithm [1]
contain Initialization Data or the key ID?

If we choose to report an event, we need to decide what data to report in the
event.
Step 7 of [1] says to fire a needkey event where "initData = block initData".
"block initData" was set in step 4, which says, "If the block (or its parent
entity) has Initialization Data, let block initData be that initialization
data." 

The problem is that Initialization Data may not be readily available when
decrypting. Instead, the key ID is generally what is known for a given block.

Which of the following should we specify?
1) The needkey event contain the Initialization Data, which can be sent to the
server just like it can for the Potentially Encrypted Stream Encountered
algorithm [2]. This has implementation overhead.
2) The key ID of the current block. This is easier to implement but
inconsistent with the Potentially Encrypted Stream Encountered algorithm [2]
and may not be useful for obtaining a key. This option is probably better if we
have a separate even name and/or fire it at different objects.


[These footnotes apply to all three updates through this one.]

^ Is this true for CENC, even in use cases case that involve key rotation?

[1]
http://dvcs.w3.org/hg/html-media/raw-file/tip/encrypted-media/encrypted-media.html#algorithms-enrypted-block
[2]
http://dvcs.w3.org/hg/html-media/raw-file/tip/encrypted-media/encrypted-media.html#algorithms-encrypted-stream

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