Contents of the unique device ID registers LOT_NUM

[MMora.6]

I'm using STM32L031E6Y6 for a high volume low cost product and I'm hoping to arrange it so that even if my firmware binary were to be stolen, it could only be used to produce a limited number of counterfeit products.

I can cryptographically fix the firmware so that it will only run if the LOT_NUM part of the device ID registers is within a certain range but how many unique devices might share the same lot number ?

Also, is it probable that all the devices on a reel share the same lot number and is it possible to discover the lot number(s) before flashing the devices ?

[Piranha]

The one, who can pull the firmware from a protected MCU, definitely can also patch that firmware to bypass the ID test.

[MMora.6]

You're correct of course but I'm more concerned about someone in my supply chain copying the firmware that I give them. I'm not expecting to make it impossible, just more difficult and I'm hoping to do it without spending a lot of money.

[Piranha]

There are flashers that can be operated standalone without PC and can be locked to not allow the readout of stored files. Consider using such devices at manufacturing. For examle:

https://www.segger.com/products/flasher-in-circuit-programmer/