Where to store software license key

[bonmotwang]

Hello.

I am developing a product use ESP32 module.
The firmware image will be released / sold with a license key based on MAC address on each module.
My question is:
- Is it a good idea to use nvs_storage.c lib to save the key?
- Is it internal flash or SPI to the external. If it is external, it doesn't work for me because people can just copy the whole external flash.

Thanks

[ESP_Sprite]

There is no internal flash, although you could perhaps use the eFuses for license purposes. If you do want to use the flash, I'd suggest you look into SecureBoot / flash encryption: that both makes it impossible to just copy the flash (as it's encrypted with a key that only the paired ESP32 knows) as well as read out the firmware and patch the licensing code.