I've been wondering why hibernate didn't work with encryption, because this seems like the extremely obvious way to handle it, but I have struggled to find anything about it for years - glad to hear it does exist!

But yeah, also rather obviously it's inherently a bit leak-prone. Though it seems probably pretty simple to test, just hibernate and scan all stored data. They could probably even do it on shutdown, as a hash of the key data would be sufficient to detect the key.