JSObfu

JSObfu is a Javascript obfuscator written in Ruby, using the rkelly-remix library. The point is to obfuscate beyond repair, by randomizing as much as possible and removing easily-signaturable string constants.

Installation

To use JSObfu in your project, just add the following line to your Gemfile:

gem 'jsobfu'

Or, to install JSObfu on to your system, run:

$ gem install jsobfu

Documentation

Generated documentation is hosted on Github.

Example Usage

Obfuscating a Javascript string in ruby:

require 'jsobfu'

source = %Q|
  // some sample javascript code, to demonstrate usage:
  this.send_websocket_request = function(address, callback) {
    // create the websocket and remember when we started
    try {
      var socket = new WebSocket('ws://'+address);
    } catch (sec_exception) {
      if (callback) callback('error', sec_exception);
      return;
    }
    var try_payload = function(){
      TcpProbe.send("AAAAAAAAAAAAAAAAAAAAAAAAAA"+
                    "AAAAAAAAAAAAAAAAAAAAAAAAAA"+
                    "AAAAAAAAAAAAAAAAAAAAAAAAAA");
    }
    // wait a sec, then start the checks
    setTimeout(check_socket, WS_CHECK_INTERVAL);
  };
|

puts JSObfu.new(source).obfuscate

Will produce something that looks like:

this[((function () { var A="st",K="ket_reque",P="_send_webs",Z="oc"; return P+Z+K+A }
)())]=function(\u006b,U){var e;try{var B;var B=new window[(function () { var G="t",Rr
="e",C="We",$="bSock"; return C+$+Rr+G })()]((function () { var R9='/',x='s:/',xe='w'
; return xe+x+R9 })()+k);} catch(a){if(U)U((function () { var b='or',cF='r',E='e',f='
r'; return E+f+cF+b })(),a);return;}var e=function(){window[(function () { var t="e",
L="pProb",j="T",z="c"; return j+z+L+t })()][((function () { var zp="d",D="sen"; retur
n D+zp })())]((function () { var KL="AAAAAAAAAAAA",y6="AAAAAAAAAAAAAA"; return y6+KL
})()+String.fromCharCode(0x41,0x41,0101,0101,65,65,0x41,65,0101,65,0x41,0101,0x41,010
1,0101,0101,65,65,0x41,0x41,0x41,65,65,0101,0x41,0x41)+String.fromCharCode(0x41,0x41,
0x41,65,0x41,0101,0x41,0x41,0101,0101,0101,0101,0101,0101,0101,0101,0x41,65,65,65,010
1,0x41,0101,0x41,0101,0101));};setTimeout(this[((function () { var TF="et",D="k",B="c
heck_s",S="oc"; return B+S+D+TF })())],('Mcc'.length*51+47));};

Encode from the command line:

$ cat source.js | jsobfu 3

Options for obfuscation iterations and global object names can be passed:

JSObfu.new(blah).obfuscate(iterations: 3, global: 'this')

Memory Disruption

Obfuscation of this type can cause completely different memory footprints on every run. This can be annoying in some instances (like during a heap spray). To avoid this, a memory_sensitive option is provided:

JSObfu.new('var me = "BAR";\nvar description = "FOO" + me;').obfuscate(memory_sensitive: true)
#=> var y="BAR";var x="FOO"+y;

Note that the variables are still randomized and whitespace is stripped, but the String transformations are omitted.

Obfuscating multiple inputs

Typically you will want to create a new JSObfu instance per script you create, but sometimes you need the ability to generate obfuscated code on-demand that is compatible with other, already obfuscated scripts in the page. To do this you can reuse a JSObfu instance by replacing its code member:

j1 = JSObfu.new('var JSObfu = 1;')
j1.obfuscate           #=> 'var y = 1;'

j1.code = 'var Value2 = JSObfu + 2;'
j1.obfuscate           #=> 'var x = y + 2;'

Alternatively, you can persist the instance's #scope (which contains a map of top-level variable renames) and pass it into a new instance of JSObfu later:

j1 = JSObfu.new('var JSObfu = 1;')
j1.obfuscate           #=> 'var y = 1;'

j2 = JSObfu.new('var Value2 = JSObfu + 2;', scope: j1.scope)
j2.obfuscate           #=> 'var x = y + 2;'

Deobfuscation

Just as coding these transformations is possible, so is the inverse. Hats off to @m1el for creating a jsobfu deobfuscator! Don't forget, jsobfu will never stop a determined analyst; but it can be very helpful against static detection.

Development Environment

Setting up is easy:

$ cd jsobfu
$ bundle install

Generating documentation

$ yard && yard server --port 9999

Then open http://localhost:9999 in your browser.

Running specs

$ rake spec

To run without integration specs, set INTEGRATION=false as an environment variable.

License

BSD-3-Clause

jsobfu

Development

Runtime