Saving multiple encrypted files as one

{
 var str, string_number, filename, i, file, j, k;
 //Remember that the str-variables have to be strings
 str[0]="The string that previously was in save_file.txt";
 str[1]="The string that previously was in save_file2.txt";
 str[2]="The string that previously was in save_file3.txt";
 str[3]="The string that previously was in save_file4.txt";
 str[4]="The string that previously was in save_file5.txt";
 str[5]="The string that previously was in save_file6.txt";
 str[6]="The string that previously was in save_file7.txt";
 str[7]="The string that previously was in save_file8.txt";
 string_number=8;
 filename="savegame.b4s";
 file=file_bin_open(filename, 1);
 for(i=0; i < string_number; i += 1)
 {
    str[i] += " ";
    //I have no idea why I have to add the above line, but it works ;)
    k=string_length(str[0]);
    if(k < 256)
    {
    file_bin_write_byte(file, 0);
    file_bin_write_byte(file, k);
    }
    else if(k < 65536)
    {
    file_bin_write_byte(file, 1);
    file_bin_write_byte(file, floor(k/256));
    file_bin_write_byte(file, k mod 256);
    }
    else if(k < 16777216)
    {
    file_bin_write_byte(file, 2);
    file_bin_write_byte(file, floor(k/65536));
    file_bin_write_byte(file, floor((k mod 65536)/256));
    file_bin_write_byte(file, k mod 256);
    }
    else show_error("String number " + string(i) + " is to large to be saved, please make it smaller. (below 16 Mb)", 0);
    for(j=1; j <= k; j += 1)
    {
        file_bin_write_byte(file, ord(string_char_at(str[i], j))^(((5*i+17)*i*i+33*i+92) mod 256));
    }
 }
 file_bin_close(file);
}

{
 var str, string_number, filename, i, file, j, k, length;
 string_number=8;
 filename="savegame.b4s";
 file=file_bin_open(filename, 0);
 for(i=0; i < string_number; i += 1)
 {
    k=file_bin_read_byte(file);
    if(k == 0)length=file_bin_read_byte(file);
    else if(k == 1)
    {
    length=file_bin_read_byte(file)*256;
    length += file_bin_read_byte(file);
    }
    else if(k == 2)
    {
    length=file_bin_read_byte(file)*65536;
    length += file_bin_read_byte(file)*256;
    length += file_bin_read_byte(file);
    }
    else show_error("String number " + string(i) + " seems to be corrupted...", 0);
    k="";
    for(j=1; j <= length; j += 1)
    {
        k += chr(file_bin_read_byte(file)^(((5*i+17)*i*i+33*i+92) mod 256));
    }
    //k now contains string number i
    //Example of how the following code can look:
    /*
    if(i == 0)
    {
        score=real(k);
        //Remember to use real when necessary
    }
    else if(i == 1)
    {
        global.kills=real(k);
        //Remember to use real when necessary
    }
    else if(i == 2)
    {
        global.player_name=k;
    }
    else if(i == 3)
    {
        player.x=real(k);
    }
    else if(i == 4)
    {
        player.y=real(k);
    }
    else if(i == 5)
    {
        player.ammo=real(k);
    }
    */
 }
 file_bin_close(file);
}