Verification of integrity after installation of GrapheneOS

Ruralmochaman

"Hardware-based attestation

GrapheneOS provides our Auditor app for using a combination of the verified boot and attestation features to verify that the hardware, firmware and operating system are genuine along with providing other useful data from the hardware and operating system.

Since the purpose of Auditor is to obtain information about the device without trusting it to be honest, results aren't shown on the device being verified. You need a 2nd Android device running Auditor for local QR code based verification. You can also use our optional device integrity monitoring service for automatic scheduled verifications with support for email alerts."

When it says u need a 2nd android device running Auditor because it doesn't trust the pixel for being honest, wouldn't this same principle apply to the 2nd android device for the local QR code based verification?

Seems like it would only be as good as the weakest link and I don't have a second android device I trust when it comes to the step.

Also it mentions Verified Boot and Attestation features that Auditor uses.

If Auditor needs those two can I just check the integrity with both of this things one being the built in attestation feature by the GrapheneOS pixel?

Or does the firmware, hardware and operating system have to be checked by a different source like what Auditor would be doing?

de0u

Ruralmochaman The checking depends on somebody being able to do a lot of cryptographic computation and able to check the results. People can't realistically do the math by hand with pencil and paper, so some computer is needed.

If the phone has been corrupted, it doesn't make sense to ask the phone to do the math and tell you that it got the right answer. Remote attestation uses a server run by the GrapheneOS project to check the math.

People who don't want to trust the GrapheneOS server can use a trusted Android phone instead.

MyIdentityIsntImportant

Ruralmochaman You can verify your installation's integrity by checking the verified boot signing key hash at device power-on. Turn off your device, power it on, and then when the message of "your phone is loading a different operating system" appears, press the power button to pause the process. Then check if the printed hash matches your phone's listed hash over at https://grapheneos.org/install/web#verified-boot-key-hash

If it does, you've got a good & verified installation. Then press the power button again to continue booting as usual.

Good luck on your privacy journey.

Ruralmochaman

de0u well that's part of what I was trying to figure out. Is when you said a trusted android device to do the checking.

If I use a corrupted android device to use Audit to check the Auditee device then it sounds like the Auditor needs to be verified somehow to make sure it will be able to reliably check it?

So to simplify Android device used is Motrolla stock android to check my pixel 8 GrapheneOS. If the Motrolla is compromised is it at all possible for that to affect whether or not the check on the pixel 8 will be accurate?

Ruralmochaman

MyIdentityIsntImportant good input. However, I believe that the GrapheneOS install guide said that you can't really trust the device to reliably tell me if the hash is right if its been compromised, isn't that why Auditor is even there?

oldschkool

@Ruralmochaman - You're over-thinking it.

Users either verify the hash as @MyIdentityIsntImportant advised or for a full audit you find a friend with an Android phone and follow instructions on the GOS usage page :[https://attestation.app/tutorial](https://)

In your case, verifying the hash is simplest way to check. Users following the installation instructions don't mysteriously get hacked installing GOS.

Ruralmochaman

oldschkool I don't mean to sound challenging but the hash check and auditor serve the very purpose of checking whether or not its been hacked in the process.

But for my situation I had lost control over many things prior to my recent factory reset. It may be reliable upon installing but the periodic checks is what I'm after. If someone can clear up my question regarding the Auditing device needing to be verified in any way to make this process reliable it'd help.

Ruralmochaman

oldschkool also my apologies because I had made a new post with updated questions, I had noticed moments ago I accidentally responded to a fairly old post of mine.

raccoondad

Ruralmochaman It may be reliable upon installing but the periodic checks is what I'm after.

That would be security theater. Secure boot removes the possibility of a system files being corrupted.

Assuming your past device had proper secure boot, you most likely weren't compromised like that. People thinking they were compromised certain way, or compromised at all, without any real reason to believe so accounts for a lot of posts here

de0u

Ruralmochaman When Auditor runs on a target device, it assembles a variety of cryptographically signed evidence into a giant QR code. In theory that QR code could be decoded and the contents could be checked by hand with pencil and paper, but it would probably take a careful person a year. In practice the QR code full of evidence must be processed by a computer program. For the computer program that decodes and checks the information in the QR code to produce a trustworthy answer, the computer must be trustworthy.

Ruralmochaman

de0u if one truly can't trust the device that they placed GrapheneOS on then they can't reasonably rely on another. At least one that's not connected to them nor in their control would likely be their best bet in securing a computer (in this case I'm trying to do from another phone) to safely decode and check the QR information as you've stated. That does answer my question, though.

Ruralmochaman

raccoondad so the hash given upon the secure boot screen shows whether or not the system files on a device would show that if any sort of compromise had happened even after the successful install?

People believing that is true. I do have a bit of an odd situation, however that I haven't delved into its description I may post at a later time a bit more of the specifics in hopes to gain a sense of direction on what next steps would be needed.

I hope I don't come across as one of those people, and I thank you for your input.

de0u

Ruralmochaman If one truly can't trust the device that they placed GrapheneOS on then they can't reasonably rely on another.

If one's threat model includes an adversary who can compromise, at the same time, every Android phone (or tablet) that one can gain access to, including new-in-box devices on shelves in retail stores, that sounds like it would be expensive to overcome.

Ruralmochaman

de0u

Expensive and also extremely difficult.

de0u

Ruralmochaman So the hash given upon the secure boot screen shows whether or not the system files on a device would show that if any sort of compromise had happened even after the successful install?

A proper Pixel bootloader observing a user-installed AVB signing key and a system image with a vbmeta partition properly signed by the user-installed AVB signing key will display the fingerprint of the user-installed AVB signing key before proceeding to boot that system image. If the system is GrapheneOS, then the system image will use dm-verity to check the signature of each part of the system image "lazily" (when it is first used). If the system gets to the unlock screen without having displayed a "corrupt" image, then the parts of the system image that were used to get to that point (plus, in practice, some other parts) were observed to be signed by the user-installed AVB signing key.

Of course, a hypothetical fake bootloader can display whatever it wants to. An important thing Auditor adds is an attestation that signatures of all parts of the boot chain, including the bootloader, pass, assuming the secure element of the particular device wasn't compromised. Unfortunately the attestation is a couple kilobytes of densely packed binary data including multiple digital signatures, so the only practical way to evaluate the claims is to use a computer.