This is a follow up to this post:
I don't see how this can work given the second bullet point:
- Kc is stored on the computer n separate times, one per user. Each instance is encrypted by a different user key Ku1...Kun.
Two related questions:
What happens when a new user is added to the system. Since that new user needs a copy of an unencrypted Kc, then it would follow that Kc is sitting on the disk somewhere, which begs the question, "Why does every user need their own self-encrypted copy of Kc?
What happens when a user is deleted from the system? In the comments of the original post, user Thomas Pornin states Kc needs to be replaced every time a user is removed from the system, which means that each user would need to get a new key every time. If this is the case, wouldn't each user need to be logged out of a current session since the data will be unreadable with their suddenly outdated key?