> How do I know my partner won't abuse my trust?
> You can't. However with Rumuki you have the discretion to only grant playbacks when you can keep an eye on them. You also have the option to revoke all playback grants and delete the recording if trust is ever lost.
There is, of course, no technological way to prevent someone from capturing a video through the analogue hole (i.e., pointing a camera to the video as it is played), even if we assume that is possible that a consumer device can be controlled to such an extent that its owner can't find a way to capture the video output digitally.
In my opinion this is fair, because the vast majority of bitter/petty ex's are not going to know how to, or bother with, reverse engineering an app to spite their significant other. They'd also have to do it when they're granted access to the app, which implies a certain forethought.
Your answer demonstrates that you've thought about this problem, not that you've solved it. I like the idea of this app, but I would argue that the core promise of your app is technically infeasible.
EDIT: I clicked through to read your whitepaper and see that you've explicitly called this concern out and admitted the DRM scheme cannot be foolproof. That's admirable, and I'm glad you did address it. I would gently suggest you place that disclaimer somewhere in your FAQ as well.
If your ex is making secret copies of sex tapes while you are still in a relationship with him, I think you have bigger things to worry about than revenge porn.
Best bet is avoiding sextapes.
If you don't understand someone's sexual preference, the correct response is no response. You're not obligated to comment on everything.
However, I bet you do remember it better than it was. So keep your memories. They're much better for this than a video record.
The app does not protect from malicious partners, it just makes sure videos are still secure if one of the phones is stolen or lost. I even think there should be a feature to backup your key to your computer or your other phone.
And again, it is a client app, assume it would be modified by a malicious party.
Just admit the problem is not possible to solve.
For example, sending a message between party A and party B so no party C can read it is possible, given that party A and party B have some way to pre-share key. Sending a message from party A to party B in a way that party B knows it is from party A but is unable to prove it to any third-party is, again, possible under some reasonable conditions, see OTR/Axolotl. Sending a message from party A to party B in a way party B can read the message but can't resend it is impossible under any conditions.
In most cases DRM-like functionality is a bullshit. Secret sharing is known to protect against outsiders only. You can use it to split backups so they are harder to steal [1]. The scheme will never work for cases when malicious party has the whole secret at some point in time.
[1] https://www.schneier.com/blog/archives/2010/07/dnssec_root_k...