[Matroska-devel] Re: Re: Encryption

Paul Bryson paul at msn.com
Tue Dec 20 20:47:11 CET 2005

"Joseph Ashwood" wrote...
> And one reason for not doing it is because anyone can remux it, creating 
> an unauthorized variation of the file, without requiring any sort of 
> decryption to occur (for example removing a "sold-to" track).

You may want to look at the SignatureSlot element.  It allows contents to be 
signed for authenticity, so if the content is changed, then the signing 
would no longer match.  I assume that if a DRM system is good enough to 
safely exchange keys, then it is good enough to be able to check that the 
file contains all required elements.

In the end, there is no way to 100% prevent unauthorized altering of files. 
No matter how DRM'd a file is, I can always capture video being sent to the 
overlay and audio being sent to the sound card.  But DRM decoders requiring 
certain signed elements should work for any 'reasonable expectations' for 
file protection.

Of course this does not at all address any weaknesses introduced by being 
able to determine timecode and frame type.


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