vaz83:
The idea would be storing the key in the code itself, but leaving some json files on the flash memory encrypted. I know there is always a way, but at least i am protecting my data at some sort of level. Can you point me in any direction ?
Then on the other hand this is just obfuscation as DrAzzy said. You could store the key on an external EEPROM chip or an sd card which you insert before operation and remove after operation (much like online banking dongles work).