But the comment space below your message is just enough . The only way i can think of ad hoc is to make use of the limit of the speed of light load a bunch of private keys onto a space probe , shoot it into space . Destroy any local copy . Program the probe to send back keys at various time intervals as it moves away from earth . Encrypt messages on earth with the public keys you kept , each one dated with an estimated arrival date of when we expect to receive the private key . The faster the probe the more secure the method . The only problem is . Its not using blockchain . Oh well . <| sep |> Oh wow , makes me cherish mine more ! Thanks for the info <| sep |> That ' s what Old Republic films can be about , and they don ' t have to be about the games .