I used opentimestamps.org to timestamp my last apartment lease after signing and before emailing it to an out-of-country landlord who I'd never met; he then signed it and time-stamped his copy before sending me a copy. That way, in case if a dispute, we both had time-stamped proof neither party had changed any lease terms before signing--- as anyone (he, I, or a court) could compare the wording and verify he didn't change what I signed before he signed. His local agent in my city didn't have signing authority for him.