If I understand well, it is now well documented that all Intel chips should be considered as back doored because of the Intel Management Engine. I guess one should now consider that all chips over a given complexity are possibly back-doored in this way or in hardware. It is also reported that the Russians are switching back to typewriters.
However mechanical typewriters can also be bugged, and it is not that convenient for file sharing, steganography of the data on images, etc.
So my question is: would the 'good' technical solution, for writing a text and encrypt it keeping the highest level of certainty that one is not spied on, be to:
put together an Arduino microcontroller (simple enough to not be back-doored), 2 SD card readers (one for SD card with text content, the other one for SD card with exclusively encrypted text content), a primitive keyboard, a simple 16 lines LSC screen, and
use the Arduino as a primitive word processor + AES encrypter
plugging only the encrypted SD card on other machines?
Do you think this would be safe? Do you think one can get a safe system in a simpler way?