The backdoor can be anywhere between the two computers (most likely at the extremities though). I agree with you in the sense that software should be made as s

The backdoor can be anywhere between the two computers (most likely at the extremities though). I agree with you in the sense that software should be made as secure as possible, my comment is just a remainder that one should be realistic about what level of security he can get. If you didn't audit the hardware your software is running on and your local isn't physically secure spending so much time on software auditing isn't very useful. You'd even have to thoroughly double check that the software you have it the one you expect, audit your compiler, audit your os and recompile everything you have. You know better than me that there is no such thing as absolute security, so you're secure relative to a menace. If you try to secure yourself against a 1st world intelligence agency, I say... "Good luck". ;)