The process of exchanging keys will theoretically leak metadata unless you already have an established secure line. In which case you will not need to open a ne

The process of exchanging keys will theoretically leak metadata unless you already have an established secure line. In which case you will not need to open a new one, defeating the purpose. Anyway, the most secure method of communication would be to leave all electronic devices somewhere far away and ideally locked in a solid metal box, then meeting in person somewhere where surveillance is hard or impossible. In the ideal case this will obfuscate all metadata including sender and receiver, unless someone happens to see you travelling to or away from the meeting place.