VCSK segments come from factories and there are many factories that produce VCSK segments. Two segments produced by the same factory have the same initial content. There is a commonly available VCSK segment factory that produces segments that are initially zero. These factories have no holes. Not even the segment keeper's logic need be trusted.
To provide copyable data with this mechanism one places his data in a VCSK segment S. When this data is complete one calls S to freeze itself and return a factory. Thenceforth S will not be writable by any key. The new factory will produce writable segments whose initial contents are those of S. A segment from the new factory is itself a VCSK segment and after possible modification can itself produce a factory generating copies of the modified segment. Thus the cycle continues.
The VCSK style segment affords a mechanism to provide copies of data stored in a segment that can be modified but where the cost of the copy is little more than the cost of the modified pages.