my $f = shift;
my $fp = `ssh-keygen -l -f '$f'`;
chomp($fp);
_die "fingerprinting failed for '$f'" unless $fp =~ /([0-9a-f][0-9a-f](:[0-9a-f][0-9a-f])+)/;
_die "fingerprinting failed for '$f'" unless $fp =~ /([0-9a-f][0-9a-f](:[0-9a-f][0-9a-f])+)/ or $fp =~ m(SHA256:([A-ZA-z0-9+/]+));
$fp = $1;
return $fp;
}