The following is extracted from this Keykos history:
Derwent had computerized some large collection of patents dealing with chemicals. They were able to search their data to identify patents describing chemicals meeting some sort of chemistry savvy criteria. Their data base and code were highly proprietary and indeed represented their main proprietary assets. Their potential customer’s queries were nearly as proprietary. Neither party was willing to send their stuff to the other party’s computer for processing. Was there a way for a trusted third party to provide a computing platform that would respect simple rules to protect the respective proprietary interests?
One scheme was conceived some years later for Derwent to charge the owner of the query program for the size (entropy) of the answer that the query program returned to the owner. The price per bit would be such that the data base owner would be willing to sell his entire DB at that price per bit. In this context confinement was strategic but did not need to be perfect. Wall banging has a cost per bit well in excess of the value of the confined data. Compression techniques are a bigger problem.

As a side note on the perverse incentives of the current patent system; it is strategic not to read patents lest upon infringement you subject yourself to triple damages.