ActionScript code protection

ActionScript code protection. To make ActionScript code as safe as possible flash developers use a variety of code encryption and obfuscation methods. Most of the methods are kept in secret because they are used in popular ActionScript obfuscators.

Overview

ActionScript obfuscators are aimed to resist Flash decompilation. Some SWF protectors implement lexical transformations - such as identifiers renaming, control flow transformation, and data abstraction transformation - that make it harder for decompilers to generate correct and usable output. Others - insert certain traps based on decompilers imperfections.

Obfuscation is the process of modifying ActionScript code. Most popular obfuscators make it impossible to use the original code for programming by mixing up functions, arguments and variables names; however the SWF file with obfuscated code stays readable for Flash players. Some decompilers manage to open protected files and maybe extract some of its resources (sounds, images, etc.), but they cannot read the ActionScript code correctly. It often happens that when protected SWF file is added to decompilation software, the latter may crash or quit unexpectedly.

Examples

The easiest way to understand the benefit of SWF obfuscation is to compare a non-protected SWF with a Protected SWF. Please look at the code below.

ActionScript 2.0

Code before obfuscation:

    stop();
    if (this.holder1 == Number (this.holder1)) {
        loadMovieNum ("jopeClipLoader5.swf", this.holder1);
    } else {
        this.holder1.loadMovie("jopeClipLoader5.swf");
     }

Code after obfuscation:

do {
        if (false) {
            (() add ().holder1);// not popped
            if (true) {
                // unexpected jump
                do {
                    stop();
                } while  (false);
                // unexpected jump
                if (false) {
                    Set("\x0B\x1A\x13\x16", true);
                } while  (true);
                do {
                    if (true) {
                        // unexpected jump
                        // unexpected jump
                        if (false) {
                        } while  (true);
                        do {
                            // unexpected jump
                        } while  (true);
                        // swfAction0xAD  hexdata 0x52,0x17,0x99,0x02,0x00,0x39,0x00,0x9A,0x01... // Unknown action
                    }
                    (() add ().holder1)[(!"holder1".holder1()).holder1].loadMovie();
                    // unexpected jump
                     /* Error1016 */
                    // unexpected jump
                    do {
                        (this);// not popped
                        if (true) {
                            // unexpected jump
                        } while  (this);
                        (this);// not popped
                        // unexpected jump
                    }
                }
            }
            if (false) {
            } while  (true);
            do {
                // unexpected jump
            } while  (true);
            // swfAction0xAD  hexdata 0x52,0x17,0x99,0x02,0x00,0x39,0x00,0x9A,0x01,0x00,0x00,0x99... // Unknown action
        }
        "holder1".holder1.loadMovie();
        // unexpected jump
         /* Error1016 */
        // unexpected jump
        do {
            (this);// not popped
            if (true) {
                // unexpected jump
            } while  (this);
            (this);// not popped
            // unexpected jump
        }
    }
}
Set("\x0B\x1A\x13\x16", true);
} while  (true);
do {
( /* Error1010 */);// not popped
if (true) {
    // unexpected jump
    // unexpected jump
    if (false) {
    } while  (true);
    do {
        // unexpected jump
    } while  (true);
    // swfAction0xAD  hexdata 0x52,0x17,0x99,0x02,0x00,0x39,0x00,0x9A,0x01,0x00,0x00,0x99,0x02... // Unknown action
}

ActionScript 3.0

Code before obfuscation:

private function getNeighbours(i:int, j:int):Array{
  var a:Array = new Array();
  for (var k = 0; k < 8; k++){
    var ni = i + int(neighbour_map[k][0]);
    var nj = j + int(neighbour_map[k][1]) ;
    if (ni < 0 || ni >= xsize || nj < 0 || nj >= ysize)
      continue;
    a.push(Cell(cells[ni][nj]));
  }
  return a;
}

Code after obfuscation:

private function getNeighbours(_arg1:int, _arg2:int):Array{
  var _local3:Array = -(((null - !NULL!) % ~(undefined)));
  var _local4:*;
  var _local5:*;
  var _local6:*;
  _local3 = new Array();
  _local4 = 0;
  for (;//unresolved jump
  , _arg2 < 8;_local4++) {
    _local5 = (_arg1 + int(!NULL!));
    _local6 = (_arg2 + int(!NULL!));
    if (true){
      _arg1 = (((//unresolved nextvalue or nextname << !NULL!) + !NULL!) 
<< undefined);
      _arg1 = (!(!NULL!) ^ !NULL!);
      (!NULL! instanceof !NULL!);
      var _local1 = (((!NULL! as !NULL!) + !NULL!) == this);
      if (!(!NULL! == !NULL!)){
        -((true << !NULL!)).push(Cell(cells[_local5][_local6]));
      }
    }
    if (!true){
      (_local6 < 0);
      (_local6 < 0);
      (_local5 < 0);
    }
  }
return (_local3);
}

See also

• ActionScript
• ActionScript Foundry
• Adobe Flash
• Obfuscated code
• SWF

External links

Adobe documentation and references

• ActionScript Technology Center
• ActionScript 2.0 Language Reference
• ActionScript 3.0 Language & Component Reference
• Flex 3 LiveDocs: Programming ActionScript 3.0