Hack The Box

Advanced Obfuscation

So far, we have been able to make our code obfuscated and more difficult to read. However, the code still contains strings in cleartext, which may reveal its original functionality. In this section, we will try a couple of tools that should completely obfuscate the code and hide any remnants of its original functionality.

Obfuscator

Let's visit https://obfuscator.io. Before we click obfuscate, we will change String Array Encoding to Base64, as seen below:

Now, we can paste our code and click obfuscate:

We get the following code:

          Code: javascript
          var _0x1ec6=['Bg9N','sfrciePHDMfty3jPChqGrgvVyMz1C2nHDgLVBIbnB2r1Bgu='];(function(_0x13249d,_0x1ec6e5){var _0x14f83b=function(_0x3f720f){while(--_0x3f720f){_0x13249d['push'](_0x13249d['shift']());}};_0x14f83b(++_0x1ec6e5);}(_0x1ec6,0xb4));var _0x14f8=function(_0x13249d,_0x1ec6e5){_0x13249d=_0x13249d-0x0;var _0x14f83b=_0x1ec6[_0x13249d];if(_0x14f8['eOTqeL']===undefined){var _0x3f720f=function(_0x32fbfd){var _0x523045='abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+/=',_0x4f8a49=String(_0x32fbfd)['replace'](/=+$/,'');var _0x1171d4='';for(var _0x44920a=0x0,_0x2a30c5,_0x443b2f,_0xcdf142=0x0;_0x443b2f=_0x4f8a49['charAt'](_0xcdf142++);~_0x443b2f&&(_0x2a30c5=_0x44920a%0x4?_0x2a30c5*0x40+_0x443b2f:_0x443b2f,_0x44920a++%0x4)?_0x1171d4+=String['fromCharCode'](0xff&_0x2a30c5>>(-0x2*_0x44920a&0x6)):0x0){_0x443b2f=_0x523045['indexOf'](_0x443b2f);}return _0x1171d4;};_0x14f8['oZlYBE']=function(_0x8f2071){var _0x49af5e=_0x3f720f(_0x8f2071);var _0x52e65f=[];for(var _0x1ed1cf=0x0,_0x79942e=_0x49af5e['length'];_0x1ed1cf<_0x79942e;_0x1ed1cf++){_0x52e65f+='%'+('00'+_0x49af5e['charCodeAt'](_0x1ed1cf)['toString'](0x10))['slice'](-0x2);}return decodeURIComponent(_0x52e65f);},_0x14f8['qHtbNC']={},_0x14f8['eOTqeL']=!![];}var _0x20247c=_0x14f8['qHtbNC'][_0x13249d];return _0x20247c===undefined?(_0x14f83b=_0x14f8['oZlYBE'](_0x14f83b),_0x14f8['qHtbNC'][_0x13249d]=_0x14f83b):_0x14f83b=_0x20247c,_0x14f83b;};console[_0x14f8('0x0')](_0x14f8('0x1'));

This code is obviously more obfuscated, and we can't see any remnants of our original code. We can now try running it in https://jsconsole.com to verify that it still performs its original function. Try playing with the obfuscation settings in https://obfuscator.io to generate even more obfuscated code, and then try rerunning it in https://jsconsole.com to verify it still performs its original function.

More Obfuscation

Now we should have a clear idea of how code obfuscation works. There are still many variations of code obfuscation tools, each of which obfuscates the code differently. Take the following JavaScript code, for example:

          Code: javascript

          [][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]][([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]])[+!+[]+[+[]]]+([][[]]+[])[+!+[]]+(![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[+!+[]]+([][[]]+[])[+[]]+([][(!
          ...SNIP...
          []]+(!![]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]])[+!+[]+[+[]]]+([][[]]+[])[+!+[]]+(![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[+!+[]]+([][[]]+[])[+[]]+([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]])[+!+[]+[+[]]]+(!![]+[])[+!+[]]])[!+[]+!+[]+[+[]]]](!+[]+!+[]+[+[]])))()

We can still run this code, and it would still perform its original function:

Note: The above code was snipped as the full code is too long, but the full code should successfully run.

We can try obfuscating code using the same tool in JSF, and then rerunning it. We will notice that the code may take some time to run, which shows how code obfuscation could affect the performance, as previously mentioned.

There are many other JavaScript obfuscators, like JJ Encode or AA Encode. However, such obfuscators usually make code execution/compilation very slow, so it is not recommended to be used unless for an obvious reason, like bypassing web filters or restrictions.