[povik]

I would especially like to see a cryptographic mechanism enforcing such middle ground. That is, a mechanism that would allow law enforcement accessing the private key or plain text, but only with some inescapable side effect which would hinder abusing that power. That may be producing a cryptographic "proof of compromise" for the person being spied on, or the spying being publicized, possibly with some delay, or something else. I am searching for an analogue of having police show up for a home search, which would notify both you and your neighbors, and cannot be done sneakily and by-the-book at the same time.

Are there some interesting candidates for such a mechanism? At first is sounds like a long shot, but there are cryptographic mechanisms achieving unintuitive results, so it may very well be possible.

[povik]

But then again there is a mechanism already, just not cryptographic, and that is police having to physically seize your device. I guess we don't need to work on this. There's nothing special about an E2E communication device compared to other things you may have in your home.

[sjy]

It is much more difficult to get data off an E2E communication device these days because mobile OSes use cryptography to mitigate the consequences of loss and theft. That is why law enforcement agencies want "the support of service providers," who can do things like deploy a backdoored WhatsApp binary, or bruteforce passcodes without triggering data loss. https://en.wikipedia.org/wiki/FBI%E2%80%93Apple_encryption_d...

[Canada]

That system simply isn't possible, or at least there are no candidates for such a mechanism at this time.