There are ways to mitigate (snapchat detects screenshots, etc) but no way to fully prevent - Someone could always use an external camera, etc.
I was just really hoping that they had come up with some sort of cool technical way to stop the ability to decode messages after XYZ time, even if they couldn't prevent it from being copied once decoded.
For example, imagine if a message were wrapped in two levels of encryption - Once from the user, and once with a key that you have to retrieve from keybase.io - If you weren't in the right time-window, you wouldn't be able to retrieve the second key.
There's lots of problems with that particular approach, which is why I was hoping they had come up with something awesome, not just asking the client nicely to delete it. It's a nice feature either way, though.
This is exactly how most DRM schemes work. You ping the keyserver a key, they check if you're still authorized, and if you are, they send you a key. There's even a bunch of tech that got built into commercial OSes [1][2] and hardware in an effort to try really, really hard not to expose decrypted content outside some protected path. But if a chunk of decrypted content is displayed on a screen, there's always the analog hole, e.g. taking pictures or a video of the display.
Nonetheless, it'd be interesting if all this effort, which got done because of the lobbying of major media rightsholders, was re-used for interpersonal communication.
I think the solution is pretty simple: encrypt with a one-time pad and then store the pad in a box that will burn that pad at your desired time; make sure no one can ever see the pad and your secret will be pretty safe.
There are ways to mitigate (snapchat detects screenshots, etc) but no way to fully prevent - Someone could always use an external camera, etc.
I was just really hoping that they had come up with some sort of cool technical way to stop the ability to decode messages after XYZ time, even if they couldn't prevent it from being copied once decoded.
For example, imagine if a message were wrapped in two levels of encryption - Once from the user, and once with a key that you have to retrieve from keybase.io - If you weren't in the right time-window, you wouldn't be able to retrieve the second key.
There's lots of problems with that particular approach, which is why I was hoping they had come up with something awesome, not just asking the client nicely to delete it. It's a nice feature either way, though.