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> What in the W3C EME standard cannot be freely implemented? As far as I know, EME is just a communications standard between the browser and components that are not part of the browser to allow those components to provide media data for the browser to display.

That, sadly, isn't the case. (It would be much better if it were!) All the existing EME modules are embedded as part of the browser, and there definitely isn't any standardised API to communicate with a module external to the browser.

All EME defines is an API on HTMLMediaElement to communicate with this abstract module, which yes, would allow the case of hiding the key from third parties to be addressed.

> All the existing EME modules are embedded as part of the browser

The CDMs used by Firefox, Chrome and Opera on Windows and Mac are distinct downloadables although the browsers handle the download automatically.

The CDMs used by Chrome for Android, Edge and Safari are bundled with the underlying platform and aren't embedded in the browser (though these browsers are bundled with their platform).

> From the browser's point of view there is not really any significant difference between a video that is encrypted for DRM and one that is encrypted for privacy. In the former case those who encrypted it want to keep the key secret from the viewer, whereas in the latter case they want to keep the key secret from third parties. To the browser, these look the same: there is encrypted video, and the browser needs something to decrypt that and hand it the decrypted data for it to display.

If you hiding the key from person who is intended recipient you are implementing a DRM, not solution that provides privacy.

The problem that you are mentioning is already solved, and you don't need to hide key from the viewer. It happens as follows:

- content is encrypted using randomly generated symmetric key

- the key is then encrypted using asymmetric public keys of recipients

The recipient has all information necessary to decrypt the information. If your goal is to hide from the recipient the one time key that is only used for the content that the recipient supposed to be able to view, then you're implementing DRM.

> For instance, couldn't EME be used to make a system to protect the privacy of people sharing personal videos

Not really. If you want to use the Clear Key key system for privacy, you need to deliver the key over https. (Plain http plus Web Crypto doesn't work against an active adversary.)

To get the key over https, the hosting page needs to be https. Then, due to cross-scheme CORS being prohibited, you also have to fetch the media (MSE segments) over https.

Since https already provides privacy, Clear Key EME doesn't add privacy value beyond protecting against untrusted CDN staff. But if you deliver some JPEGs over the same CDN, you have to trust the CDN staff anyway.

Don't try to post hoc rationalize DRM-motivated constructs as privacy measures.

You don't need an EME blackbox to protect privacy.

You simply need client-side decryption for that case, which can be done in a transparent sandbox with audited open source code.

But they're never going to agree to that, because then it would be trivial to dump the decrypted stream to a file. Right?

But it is trivial anyhow. DRM doesn't actually work, never has, never will; and attempting to criminalize it (such as mentioned elsewhere around here) will only serve to increase piracy, not decrease it.

Yes yes, I'm on your side here. The point is that if the decryption module were open-source, it would be trivial to do it, and there would be lots of implementations of it, while if it were a binary blob, it would significantly raise the bar. They know this, so they'll never agree to having it be open-source.

If we're talking about privacy (protecting the user from "the cloud") and not copy-protection (protecting our media overlords from the user) then I don't see the problem.

That's already part of the EME standard, implemented in the browser (so as open source as the browser is).

https://w3c.github.io/encrypted-media/#clear-key