First my apologies if this isn't the right forum for this but here's my problem :
- I have a black box that takes an input file and produces an output file.
- I want to sell this black box to a customer but I want to meter/limit the number of files the customer can use with this box. A counter would not be fair to the customer since they might use the box multiple times with the same input file.
- I could request the customer to send me the input file every time and I can encrypt it so that the black box would only work with my encryption. The problem with this is that the customer may not want to give me the input file.
- I could ask the customer to generate some sort of key based on each input file; I can then generate another key for the black box and send it to the customer to use. This seems like a workable solution and I would guess this kind of scheme has a known name and has been studied before.
Encryption is not my area (I'm into building black boxes) so I would appreciate if someone can point me to the right terminology to use to search for this kind of metering scheme.