> Maybe we're not talking about the same scenarios/alternatives? If I've set up whole-disk encryption with a security level I trust for my persistent storage, how is that not appropriate for the persisted hibernation state? To me, hibernation state is a subset of persistent storage needs, not some categorically different thing. The coupling between running system and persistent state seems so strong to me that I consider them one equivalence class of data and requiring one consistent protection standard.
Yes, we are talking about different scenarios. As I said, you can absolutely set up your swap to use a fixed password and then it will work fine as you describe.
> Are people concerned about the written hibernation state using the same key as the filesystem volumes?
That might be part of the concern, but it's more that it is possible to recover previous memory/swap state with a key that can reasonably be subsequently recovered.
Let's imagine a scenario where I have a secure password, that I enter into my browser, to say, access my bank's website. That's stored in memory by my browser & the GUI, but it is not normally allowed to be put on disk for security reasons. Then I hibernate my laptop and it gets written to the encrypted hibernate volume that uses a fixed password. I restore my laptop and go about my business. I might even reboot the laptop several time subsequently without thinking much about it. Then, someone finds a way to compromise the password used for swap encryption using any number of possible attacks (some you described). Now, not only do they have access to all the stuff on my computer, but they also have access to the contents of the encrypted swap volume, which unless I was lucky and the particular swap page was overwritten, the compromise goes back to the memory of the runtime from long before the machine was compromised. This would include this password that was very intentionally NOT stored on that computer, in order to avert precisely this kind of threat.
> If so, I would suggest that the swap crypto should not be conflated with the hibernation crypto.
That's another possible avenue, not that unlike what I was suggesting. It's worth noting though that these days there may not be much value in having separate passwords for swap vs. hibernate, since swap is rarely used on laptops.
They are all different security trade-offs, and it is debatable which is the right one. I don't think the current default is the right one for most users, but I do understand it.