> I wonder whether it'd be better for a duress PIN to delete existing data

Reliably deleting data at the scale of the whole data partition, a secondary user or a Private Space is fully supported but requires a reboot or shutdown to truly complete it.

After wiping key derivation material needed to obtain the key encryption keys in multiple ways and wiping the encrypted disk encryption keys, the OS can still access the data. It still has data in the page cache, in registers and elsewhere. There are still a bunch of system processes with data tied to what was removed. The OS is still fully functional after the nearly instant wipe of everything needed to recover the data again. It can still access all data other than what's encrypted with hardware keystore keys and not currently decrypted.

The wiping process for the duress PIN/password is completed with a shutdown which tears down everything, zeroes memory and provides at least a small time window where the hardware is powered off too. A reboot would also work and the boot process has explicit zeroing of memory, registers, etc.

We decided to use shutdown for the duress PIN/pasword but a reboot is a valid approach too. Our locked device auto-reboot timer feature we first shipped in 2021 relies on the zeroing done by GrapheneOS for both the process of the OS tearing down and then again during booting to return the device to Before First Unlock state.

> also create a semi plausible artificial profile to hide the deletion event.

It isn't feasible to fool forensic software so it largely wouldn't work against state actors. It nearly certainly wouldn't have helped in this situation in the news. They aren't reliant on a non-technical person sifting through a phone. They'll just hook it up to a laptop and follow the data extraction procedure which involves enabling ADB. The software is aware of GrapheneOS can guide people through dealing with anything different about it. They've had a lot of trouble with extraction via ADB for GrapheneOS since the vulnerabilities they exploit via ADB keep getting patched or blocked it exploit protections but it isn't realistic to block extraction with them having the PIN/password. They could just enable the encrypted backup service in the OS instead and then use CLI tools to extract the data from there with the seed phrase. They don't do that because they want everything rather than only nearly all app data. They also have special code to deal with apps such as Signal with their own layer of data encryption since the data taken from their app data directory is nearly all useless by itself.

There's also quite a difference between wiping and rebooting into a not very plausible environment with decoy data set up by the user in advance compared to not properly wiping and giving access to a decoy profile. Bear in mind the OS can still access nearly all data after the wipe until a reboot. It could make a best effort attempt at purging as much as possible from memory, but the OS is not designed to continue functioning with all of the data disappearing. It can't just wipe all loaded encryption keys without crashing and rebooting anyway. It also has a ton of data still around in caches and elsewhere. We don't want to just do a best effort job cleaning up as much as we can but rather reliably prevent recovering any of the deleted data.

We could definitely add a duress PIN/password which wipes only specific secondary profiles, reboots and has the device still functional with whatever data was in the main user still there. That's a feature we can add, but it's important to note that it will not hide that there was deletion of data. It's easy to detect, and it's not feasible to hide that it happened. Many steps can be taken to make it less obvious, but it will still be easy for software aware of it to detect. Even a massive overhaul designed to perfect it would not address the SSD itself giving away what happened for more advanced analysis.

We aren't going to add a decoy profile compromising the security of the device and providing a way to recover data in a state where it isn't at all unrecoverable yet. We did already plan to consider a 2nd duress PIN/password which only wipes specific secondary profiles, but we need to make it clear that it cannot stealthily wipe them to users.

Just wanted to say I appreciate your comprehensive comments in this thread. Learned a lot.