Re: Key distribution

On 13-05-10 10:25 AM, Mark Watson wrote:
> [Moving to public-html-media]
>
> Sent from my iPhone
>
> On May 10, 2013, at 6:21 AM, Casey Callaghan <caseyc37@gmail.com 
> <mailto:caseyc37@gmail.com>> wrote:
>
>> Having a look over the documentation on EME (encrypted media 
>> extensions), I find the following:
>>
>> > The user should not be restricted from accessing content for which 
>> legal rights have been obtained.
>>
>> (source: https://dvcs.w3.org/hg/webtv/raw-file/tip/mpreq/cpreq.html)
>>
>> I also find the following statement in the First Working Public Draft 
>> (https://dvcs.w3.org/hg/html-media/raw-file/tip/encrypted-media/encrypted-media-fpwd.html):
>>
>> > Support simple decryption without the need for DRM servers, etc.
>>
>> This is a necessary corollary of the previously quoted statement; if 
>> servers are needed to view legally purchased content (even if only to 
>> obtain decryption keys), then the legally purchased content will be 
>> unavailable if and while said servers are down.
>>
>> However, as soon as secure decryption is discussed, I find that a DRM 
>> server begins to form a vital part of the process. I have no doubt 
>> that many content providers will accept only the most secure 
>> decryption methods for their content; this leads to well-known 
>> problems should the content provider's servers ever go offline.
>>
>> This can be mitigated, to some degree, with multiply redundant 
>> servers or cloud computing. However, these solutions may be expensive 
>> and are unlikely to be kept running when it would be unprofitable to 
>> do so (for example, when the sales of a given piece of media have 
>> ended; possibly after an interval after that ending). This could also 
>> be impractical for smaller content providers, without large budgets.
>>
>> Therefore, in order to resolve this, I would like to propose for 
>> consideration the following idea (based on the serverless encryption 
>> scheme for Bitcoin):
>>
>> - that, when a user purchases legal access to a given piece of media, 
>> a message (signed with the content provider's private key) must be 
>> sent to all clients informing them of this purchase;
>> - that all clients may (and are indeed encouraged to) keep a record 
>> of all such messages from all providers;
>> - that any client, in possession of both the signed message from the 
>> content provider (verified by means of the content provider's public 
>> key) giving a given user legal permission to view certain media, and 
>> the data required to decrypt that media (either the CDM or the key 
>> obtained from the same content provider), may provide either the CDM, 
>> or the key, or both to the user on authorised request.
>> - that any client which does so must inform the content provider's 
>> server and all other clients of such access, if the key is limited in 
>> any way.
>>
>> In this way, a DRM server going offline does not prevent a user from 
>> viewing content to which they purchased a valid license before the 
>> server went offline. This appears to be a necessary consequence of 
>> the stated aims of this standard.
>>
>
> You are making an assumption that the legal rights purchased are 
> perpetual and independent of the continued operation of the service 
> from which they are purchased.
>
> This may not be true in all cases and indeed may never be true for 
> exactly the reasons you give above.
>
> For example, in the case of Netflix, the legal right to watch the 
> content extends for only 8 hours or until the Netflix client 
> application is closed, whichever is sooner. After that the right must 
> be requested again and this is only possible if Netflix servers are 
> still operating and you are still a subscriber.
>
> I would agree that the mechanism above is an interesting concept for 
> perpetual, service-independent rights, but support for this case is 
> not one of our requirements (as discussed in the bug titled 'EME 
> depends on servers with a finite life' - I don't have the number to hand).
>
> ...Mark
>
>> Casey
So: if, as a content provider, one wishes to sell, rather than lease 
access to, a copy of one's own work, one cannot depend on this scheme to 
protect one's rights, as one's right to sell rather than lease is not 
provided for at all ...

-- 
B. Ross Ashley
registered Linux user 548111