A whack-a-mole game the FBI has no chance of winning. How? Keep the de/encryption software simple, dirt simple, just open source C code, run as a command line

A whack-a-mole game the FBI has no chance of winning. How? Keep the de/encryption software simple, dirt simple, just open source C code, run as a command line program on, say, an old PC/DOS system with no hard disk. For encryption, just put the file on, say, a smartphone, to be encrypted on a diskette, give the diskette to the PC, erase the orignal file from the smartphone, have the command line C code on the PC do the encryption and write the results as a base 64 file to a diskette, and, with no effort at all at encryption or security, let the smartphone read the diskette and send the file. Simple. Just keep it simple, just dirt simple, really small, open source code. The de/encryption has to be, what, just a few loops in C, in a few hundred lines of code? The rest is just dirt simple C file I/O just one byte at a time? So, very much do not want some 100,000 line app with the de/encryption buried deep inside somewhere. And want the de/encryption run on some other device, maybe an old PC/DOS machine with no hard disk and no network connection. Or get a Raspberry Pi running some simple operating system and where can be sure that no important data will be left on the computer.