AES Bootloader for ATmega2560

I want an implementation of aes in at-mega2560's bootloader. Also, I want to explain me in complete how: 1. I can pass the key in the bootloader 2. I will lock the bootloader, in order nobody can read the key 3. I will encrypt the code 4. I will update the code In general, what I want to achieve is in case that somone reads my chip, he wouldn't can make another one same. Also, I want to have the ability of updating, without need to erase the chip.