Copy-protected Arduino-like bootloader and .hex scrambler

I wish for a (python 2.7.x) script to scramble a .hex file, , so that it will only work on Atmega328 microcontrollers with proper (descrambling) bootloader. So: (the text file explains how a firmware looks) 1: a python script must open an original file, lets call it "[login to view URL]" scramble/encrypt the data fields, and generate new checksum for each line, outputting it as a new "firmware..[login to view URL]" 2: the bootloader (attached), must be modified to descramble/decrypt the data before saving to EEPROM The goal is to be able to let people upgrade their microcontrollers by uploading a freely distributed .hex , making sure the software will run only on microcontrollers from me.