sub gen_random_key{
    ####sub fisher_yates_shuffle {
    my @array = split ("", $alpha);
    my @alpha = @array;
    for (my $i = @array; --$i; ) {
        my $j = int rand ($i+1);
        next if $i == $j;
        @array[$i, $j] = @array[$j, $i];
    }
    for (0..$#alpha){
        $decrypt{$alpha[$_]} = $array[$_];
        $encrypt{$array[$_]} = $alpha[$_];
    }
    #ensure a derangement
    for (0..$#alpha){
        if ($alpha[$_] eq $array[$_]) {
            gen_random_key();
            #warn 'key not deranged, setting another..';
            return;
        }
    }
}