> I mean - yes? If you design a subtle duress pin that only hides certain things, users would have to choose what.

That's not what we were talking about. This is the full sentence we wrote:

"Reliable deletion of data requires setting it up to be reliably deleted later on by having it encrypted on storage with keys which can be reliably prevented from ever being obtained again."

What we're saying is that in order to have fine-grained deletion of data, it has to be encrypted with fine-grained keys with hardware support for deleting those keys reliably. Reliable deletion of data should also not be confused with stealthy deletion of data which is not generally possible for the kinds of data being discussed.

> I myself want the bank apps, password manager and email to disappear without a trace

You can put all of this into a Private Space or secondary user where it can be reliably deleted as a whole. There will be no way to recover any of the data if the profile is deleted. We have a planned feature for either a toggle to make the duress PIN/password only delete specific secondary profiles or more likely a 2nd duress PIN/password with that different purpose.

Deleting secondary profiles will reliably prevent recovering any of their data, at least after a reboot or shutdown. The best way to do it would be deleting them and then rebooting where the main user and secondary profiles not included in the deletion would still be there after the reboot. Without the reboot, it's unrealistic to reach the point where it's truly highly reliable. The OS does purge the keys for a secondary profile but a lot lingers around in system processes, page cache and elsewhere. If you delete a secondary profile with the goal of preventing data recovery then it's a good idea to reboot afterwards.

Dividing things up into secondary users is the way people can set up having fine-grained reliable deletion of the data. We can expand our duress PIN/password feature to support working with that.

It should be noted nothing about wiping secondary profiles is stealthy. It's very obvious there were profiles and that they were wiped. It can be determined when it happened and approximately how much data was deleted too. The data and filenames are unrecoverable but a fair bit of metadata on the sizes of files, etc. can be recoverable because that metadata is globally encrypted rather than per-profile encrypted. If you want to delete absolutely all traces of it in a reliable way, an overall wipe of the device does it extremely well. If you delete a profile then nothing encrypted by it can be recovered but what about all the evidence of it existing in the system and Owner user data? It's in the battery statistics, data usage statistics, package manager metadata and many other places. It can be purged from those but absence of data can be detected, and there's the usual problem of simply not being able to reliably delete data from computers in a fine-grained way. It's too late to reliably delete data from a file after the file has been regularly rewritten and modified.

Deletion needs to happen through deleting the keys used to encrypt all data which was ever stored in the file, so it would have had to be set up with that in advance. To reliably redact data in a file, the file would need a dedicated hardware-backed key with a new one being generated and the old one wiped as part of redacting data. Reliable wiping of a profile or the overall device works because it's all encrypted with filesystem-based full disk encryption using keys which can be reliably deleted. Profiles have fine-grained encryption for filenames and file data.

You cannot retroactively decide you want to reliably delete the data of a specific app and then do it. It's already spread all over the place. You'd need to wipe the whole profile or the whole device if it's not in a secondary profile. The OS would have had to set up a dedicated encryption key for that app's data with hardware support for deleting only that key by itself. Apps can do this and Signal is an example of app doing it which prevents backing it up via the OS backup system without also using their own backup system too.