paps I’m hesitant to enter my PIN because I’m unsure if it’s possible to backdoor the GrapheneOS boot process.
bagel afaik that kind of tampering should not be possible under normal circumstances
secrec If a device has been outside of your physical control, all bets are off. You should NOT enter your pin, just go straight to factory reset and probably even reinstall GrapheneOS
Here's my answer from last week to someone else with the same concern:
https://discuss.grapheneos.org/d/26248-leaving-bootloader-unlocked/48
Wiping your data would do nothing to secure “your” “phone”. You go into a phone shop. You buy a Pixel phone to install GrapheneOS on it. How can you know it's an authentic, untampered Pixel phone? The state confiscates your phone. They want to attack you and get all your data. They give you a device looking like your phone. How can you know it's your authentic, untampered Pixel phone?
Purchasing an authentic Pixel phone, not a counterfeit or something that has a hardware modification that spies on you, is very important. Why are you willing to “buy” a “phone” from a state attacker that you know (once they actually confiscate your phone) are trying to get your data? This makes no sense and there's absolutely nothing you can do to secure the device they give you. Throw it to the trash and buy a new one.
Nothing can be done to secure a “phone” that was “bought” from law enforcement officials that have an interest to harm the person they “sold” this “phone” to. It's not necessary for them to tamper with the original confiscated phone in any way.
It's not necessary to reinstall GrapheneOS, I'd even say that's dangerous because (what you probably mean) it involves unlocking the bootloader, which is another opportunity to install an unofficial version of GrapheneOS that's not signed by GrapheneOS's official signing keys. It's better to reboot the phone and confirm that the hash matches while keeping the bootloader locked. Even then, that's only useful assuming that the hardware is trustworthy (a wild assumption since the “phone” was “bought” from law enforcement). There can be other modifications that can't be detected, such as an independent microphone+antenna inserted into the shell of the phone, not connected to the other hardware inside it. The microphone records, the antenna transmits. Wiping data or reinstalling GrapheneOS would do nothing to secure a phone with modified hardware, and the bootloader shouldn't be unlocked if it's already locked with GrapheneOS's official verified boot key.
bagel you could verify that it's still running graphene here
The hash cannot be trusted because the hardware cannot be trusted. Using the Auditor app might be better, but is still very problematic because (among several other reasons) Auditor can't possibly detect all hardware modifications to the phone.
paps but if I'm not able to get around the issue I'm confident that wiping device and installing GOS again is safe enough to give device to someone running with stock Android
You would have to disclose that you “bought” the device from law enforcement officials instead of from a phone shop. Not disclosing this would be immoral/fraud…