Let's say I'm selling a device with my software pre installed whose license is GPL v3. I want to prevent an unauthorized OS from being installed. According to GPL v3, I will have to share the private key with the user that can sign the image that will be accepted by the device.
My question is, when am I required to share the key? Can I share the key only when the user requests it? Can I stop sending updates and stop providing phone support if the user asks for the signing key? (Assuming it's already part of terms and conditions)