Good question.

I think the current best solution to this dilemma is to let them produce it with FLASH and deliver it to you for final ISP code downloading. You can provide them with merely testing and debugging code. They can't sell it, they can't understand it.

Just make sure you don't program a license with the same information in every copy. Avoid ascii text messages in license data because it just movitates and invites workarounds.
- - - - - - - - - - - - - -

iButtons are not secure as people think. That's all I say on that subject for now.

I know a Canadian company that did this with a clip-in iButton. It was designed to be accessible next to his snap in automotive style fuses. I'm sure it looked good on paper BUT you merely have to kick the device to unclip the metallic iButton and allow it to bridge the fuse junctions. I hear that its quite colorful. :)

- - - - - - - - - - - - - -

You could simply make you license token the reel of preprogrammed and security fused microprocessors.

There are other techniques wherein you build a fixture to reside in the manufacturers facility and with its encloded PC, it downloads a validation code into FLASH and awaits results to insure the circuitry is reasonable working, then sends a message to the faxture's PC to license it a copy of the program and encode it with tracking identifiers and code. Validate the code as running, and blow the security fuses.

Then raise the RobotWars Metal Gate and eject the PCB and load the next one. Include a small paper printer to validate accounting inclase the PC locks. I'd recommend putting it in a metal cage and schedule regualr visits to check the license allocations and look for bypasses.

If you want to talk about techniques to complicate disassembly... that's another topic. I think Embedded Systems magazine had an article on that a few months ago.

-Jay C. Box