Can someone explain me how jjencode works and if is good to use it on my code

Question

Can someone explain me how http://utf-8.jp/public/jjencode.html works and if is good to use it on my code? The first time I tried it I thought that I needed to have some kind of algorithm in my code to use it, but it works on every site. What is happening?

I already read the source code but I don't understand it.

Answer 1

Here is the commented script http://corkami.googlecode.com/svn-history/r399/trunk/misc/jjencode.txt

// this is a commented source of a jjencode script
// jjencode, http://utf-8.jp/public/jjencode.html

// reference: Peter Ferrie, 2011, http://pferrie2.tripod.com/papers/jjencode.pdf

// for reference,
// alert("Hello, JavaScript" )
// is encoded as 

// $=~[];$={___:++$,$$$$:(![]+"")[$],__$:++$,$_$_:(![]+"")[$],_$_:++$,$_$$:({}+"")[$],$$_$:($[$]+"")[$],_$$:++$,$$$_:(!""+"")[$],$__:++$,$_$:++$,$$__:({}+"")[$],$$_:++$,$$$:++$,$___:++$,$__$:++$};$.$_=($.$_=$+"")[$.$_$]+($._$=$.$_[$.__$])+($.$$=($.$+"")[$.__$])+((!$)+"")[$._$$]+($.__=$.$_[$.$$_])+($.$=(!""+"")[$.__$])+($._=(!""+"")[$._$_])+$.$_[$.$_$]+$.__+$._$+$.$;$.$$=$.$+(!""+"")[$._$$]+$.__+$._+$.$+$.$$;$.$=($.___)[$.$_][$.$_];$.$($.$($.$$+"\""+$.$_$_+(![]+"")[$._$_]+$.$$$_+"\\"+$.__$+$.$$_+$._$_+$.__+"(\\\"\\"+$.__$+$.__$+$.___+$.$$$_+(![]+"")[$._$_]+(![]+"")[$._$_]+$._$+",\\"+$.$__+$.___+"\\"+$.__$+$.__$+$._$_+$.$_$_+"\\"+$.__$+$.$$_+$.$$_+$.$_$_+"\\"+$.__$+$._$_+$._$$+$.$$__+"\\"+$.__$+$.$$_+$._$_+"\\"+$.__$+$.$_$+$.__$+"\\"+$.__$+$.$$_+$.___+$.__+"\\\"\\"+$.$__+$.___+")"+"\"")())();


// preliminary points

// (a + "") gives the string representation of a

// [] = empty array. 0 by value, -1 with ~ => ~[] = -1
// as a string, ![] gives  'false'

// {} = empty object.
// as a string, {} gives '[object Object]'

// if a is a x-long array, a[x] is 'undefined' as a string. same for absent properties.

// "" is an empty string. !"" returns 'true' as it is indeed 'null'


// now let's start with the actual code

// creating $ variable with a value.
 $=~[]; // $ = -1

 // defining properties of a $ object.
 $ =
 {
   ___:++$,             // 0, $ = 0

   $$$$:(![] + ””)[$],        // 0th char of 'false',           => 'f'

   __$:++$,             // 1, $ = 1 now...

   $_$_:(![] + ””)[$],        // 1st char of 'false'            => 'a'

   _$_:++$,             // 2...

   $_$$:({} + ””)[$],         // 2nd char of '[object Object]'  => 'b'

   $$_$:($[$] + ””)[$],       // 2nd char of 'undefined'        => 'd'

   _$$:++$,             // 3...

   $$$_:(!”” + ””)[$],        // 3rd char of 'true'             => 'e'

   $__:++$,             // 4

   $_$:++$,             // 5

   $$__:({} + ””)[$],         // 5th char of '[object Object]'  => 'c'

   $$_:++$,             // 6

   $$$:++$,             // 7

   $___:++$,            // 8

   $__$:++$             // 9
 };

// => in order, ___, __$, _$_, _$$, $__, $_$, $$_, $$$, $___, $__$, $_$_, $_$$, $$__, $$_$, $$$_, $$$$ are now equal to 0...F,
// note they are just binary numbers with character substitution

$.$_ =
    ($.$_ = $ + ””)[$.$_$] +              // 5th character of '[object Object]'  => $.$_ = 'c'
    ($._$ = $.$_[$.__$]) +                // 1st character of ...                => $._$ = 'o'
    ($.$$ = ($.$ + ””)[$.__$]) +          // 1st char of 'undefined'             => $.$$ = 'n'
    ((!$) + ””)[$._$$] +                  // 3rd char of 'false'                 => 's'         // poor s, we don't save it...
    ($.__ = $.$_[$.$$_]) +                // 6th char of '[object Object]'       => $.__ = 't'
    ($.$ = (!”” + ””)[$.__$]) +           // 1st char of 'true'                  => $.$  = 'r'
    ($._ = (!”” + ””)[$._$_]) +           // 2nd char of 'true'                  => $._  = 'u'
    $.$_[$.$_$] +                         // 5th char of '[object Object]']      => 'c'         // hey, we already have a c !
    $.__ +                                // 't'
    $._$ +                                // 'o'
    $.$;                                  // 'r'

// => $.$_ = 'constructor'


$.$$ =
    $.$ +                       // 'r'
    (!”” + ””)[$._$$] +         // 'true'[3] => 'e'
    $.__ +                      // 't'
    $._ +                       // 'u'
    $.$ +                       // 'r'
    $.$$;                       // 'n'

$.$ =
    ($.___)[$.$_][$.$_];        // (0)[constructor][constructor]


// summary of $ at this point

// $ = {}
// $.___  = '0';
// $.__$  = '1';
// $._$_  = '2';
// $._$$  = '3';
// $.$__  = '4';
// $.$_$  = '5';
// $.$$_  = '6';
// $.$$$  = '7';
// $.$___ = '8';
// $.$__$ = '9';
// $.$_$_ = 'a';
// $.$_$$ = 'b';
// $.$$__ = 'c';
// $.$$_$ = 'd';
// $.$$$_ = 'e';
// $.$$$$ = 'f';

// $.$_ = 'c'
// $._$ = 'o'
// $.$$ = 'n'
// $.__ = 't'
// $.$  = 'r'
// $._  = 'u'

// $.$_ = 'constructor';
// $.$$ = 'return';
// $.$ = (0)[constructor][constructor]



// and finally, the only line of call

$.$(
    $.$(
        $.$$ + ”\”” + ENCODED + ”\””
        )()
    ) ();

//
(0)[constructor][constructor](
    (0)[constructor][constructor](
        return + " + ENCODED + "
        )()
    )()

// 'equivalent' to eval(eval(ENCODED))


// encoding
// !"#$%&’()*+,-./:;<>=?@[]^_`{|}~  as is
// 0123456789abcdeftou => as $ properties. Ex : 'babe' = $.$_$$ + $.$_$_ + $.$_$$ + $.$$$_
// other ascii chars: as \xxx (octal) encoding. Ex: 'A' = char(65) = \101 = "\\" + $.__$ + $.___ + $.__$
// unicode chars as \u????. ex: 'sea', \u6d77 as "\\" + $._ + $.$$_ + $.$$_$ + $.$$$ + $.$$$

// so in the end, it's just defining a $ object and executing an eval on a string, that is built character by character.

// to confirm, here is a small imperfect python decryption script

// import sys
// start = r'$=~[];$={___:++$,$$$$:(![]+"")[$],__$:++$,$_$_:(![]+"")[$],_$_:++$,$_$$:({}+"")[$],$$_$:($[$]+"")[$],_$$:++$,$$$_:(!""+"")[$],$__:++$,$_$:++$,$$__:({}+"")[$],$$_:++$,$$$:++$,$___:++$,$__$:++$};$.$_=($.$_=$+"")[$.$_$]+($._$=$.$_[$.__$])+($.$$=($.$+"")[$.__$])+((!$)+"")[$._$$]+($.__=$.$_[$.$$_])+($.$=(!""+"")[$.__$])+($._=(!""+"")[$._$_])+$.$_[$.$_$]+$.__+$._$+$.$;$.$$=$.$+(!""+"")[$._$$]+$.__+$._+$.$+$.$$;$.$=($.___)[$.$_][$.$_];$.$($.$($.$$+"\""+'
// end = r'+"\"")())();'
// 
// with open(sys.argv[1], "rb") as f:
//     r = f.read()
// 
// r = r.replace(start, "").replace(end, "")
// print r
// 
// subst = [
//     ['$.$___','8'],
//     ['$.$__$','9'],
//     ['$.$_$_','a'],
//     ['$.$_$$','b'],
//     ['$.$$__','c'],
//     ['$.$$_$','d'],
//     ['$.$$$_','e'],
//     ['$.$$$$','f'],
//     ['$.___','0'],
//     ['$.__$','1'],
//     ['$._$_','2'],
//     ['$._$$','3'],
//     ['$.$__','4'],
//     ['$.$_$','5'],
//     ['$.$$_','6'],
//     ['$.$$$','7'],
//     ['$.$_', 'c'],
//     ['$._$', 'o'],
//     ['$.$$', 'n'],
//     ['$.__', 't'],
//     ['$.$', 'r'],
//     ['$._', 'u'],
//     [r'"\\"' , '\\'],
//     ["\"\\\\\\\\\"", "\\\\"],
//     ["+", ""],
//     ]
// 
// for s in subst:
//     r = r.replace(s[0], s[1])
// 
// r = r.replace("+", "")
// print r

// Ange Albertini, BSD Licence 2011