Added the -G option to allow logins only for users that are members of a certain group. This allows finer control of an instance on who can and cannot login over a certain instance (e.g. password and not key). Needs double-checking and ensuring it meets platform requirements.

open(IN,"<crypt.ind");
open(OUT,">crypt.ind.tmp");
$a = <IN>;
print OUT  "$a\n\\addcontentsline{toc}{chapter}{Index}\n";
while (<IN>) {
   print OUT $_;
}
close OUT;
close IN;
system("mv -f crypt.ind.tmp crypt.ind");