Revocation is possible by either changing the address of the data (e.g. by adding a nonce), by changing the encryption key, or ideally both. This is laregly a moot distinction, since encrypting data with a new key changes the protocol-level data (the encrypted blocks), and thus the address.
If another user has a copy of the data being revoked, either by having it on their local disk or with a hard link to the same CID, they will have continued access to this data. This is the same as having downloaded a copy of the data previously — we can’t reach into someone else’s computer and delete files.
Note that removal of access via rotation is a very wide action. Subdeleation of read access of that data when not in a child relationship needs to be re-granted.
Once a new key is used for the data, authorized users need to be granted the new key.
The Web Native File System handles this via the
shared_with_me segments. If there’s a ”cache miss” in your
shared_with_me, you may check the target file system’s
shared_by_me segment, and look up the new key.
This extends to other resources as well. The WNFS happens to be an effective data-layer substrate for key exchange broadly.