When your moneysack is bottomless you can do anything, no need to decrypt it, man-in-the-middle it, if that cant do, switch the victims CPU for your own "special" one. Intelligence organizations have been breaking silently into peoples homes for hundreds of years, its a skill well developed. To then change a chip on your computer, is peanuts.
Why would you bother with CPU switching and such when you could just install an old fashioned microphone? If you were actually inclined to eavesdrop, it seems like hardware-subverting your PC is a lot more expensive and fragile than software or a specialty purpose bug elsewhere in the room.
I vaguely remember hearing other stories where chips were made with secret backdoors in them, but I can't seem to find any.