More than 1 year has passed since last update.

古いマシン

gpg --export -a FFFFFFFF > public.asc
gpg --export-secret-keys -a FFFFFFFF > secret.asc

新しいマシン

gpg --import public.asc
gpg --import secret.asc
gpg --edit-key FFFFFFFF (and set the trust level and whatever else.)