Recovery possibilities with Zero knowledge encryption


I have some encryption understanding however I fail to get my head around following scenarios. I would like to know if they are possible with a zero knowledge encryption system.

What the system can or can’t do can be added to the answer. Example:

  • The system needs to keep a encrypted copy of the key.
  • The user has to have the key on a USB stick.

In the end, all scenarios ask the same questions.

  • Can the user access his data?
  • Does the system know about his data?

Scenario 1: User logs in on a new computer. Does not have the key with him.

Scenario 2: User logs in on a new computer. Does have the key with him (e.g. USB stick).

Scenario 3: User lost his password. His identity has been verified and approved.

Scenario 4: New sub-users are assigned to the same resource.