If I had to guess, when you set up an Android device's passcode, it generates a key pair, signs a message and ships the public key to Google, and then encrypts

If I had to guess, when you set up an Android device's passcode, it generates a key pair, signs a message and ships the public key to Google, and then encrypts the private key with your pin (maybe with your Google password and/or a Google-provided salt at the end) and ships that to Google. So when you restore access on a new device, it downloads that private key bundle and tries to decrypt it using the PIN you provide. > And what's stopping the FBI from asking Google to send them every device's PIN as it's created? device PINs are never sent to Google in this scenario - but nothing is stopping them from being asked to log your Password the next time you sign in, and it's up to you to trust that they'd never do this even when asked via national security letter since it destroys all trust people (and Google Workspace enterprise businesses) have in their login system.