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LLXX
July 25th, 2006, 17:45
I encountered this function in a Javascript packer/protector (yes, they do exist! easy to unpack though...)
Code:
function x(x) {

 var l=x.length,b=1024,

 i,j,r,p=0,s=0,w=0,

 t=Array(63,32,52,0,57,54,51,13,20,26,0,0,0,0,0,0,5,39,41,45,11,10,16,37,29,55,12,33,42,60,19,3,49,47 ,22,21,56,50,4,18,44,48,61,0,0,0,0,30,0,34,27,14,25,15,46,9,59,6,7,62,36,58,43,8,28,35,40,38,24,23,1 ,2,31,17,53);



 for(j=Math.ceil(l/b);j>0;j--) {

  r='';

  for(i=Math.min(l,b);i>0;i--,l--) {

   w|=(t[x.charCodeAt(p++)-48])<<s;

   if(s) {

    r+=String.fromCharCode(165^w&255);

    w>>=8;s-=2

   } else {

    s=6

   }

  }

  document.write(r);

 }

}
It takes as input a huge long string (the ciphertext, which appears to be base-64) and transforms it into cleartext HTML.

I'm just wondering if anyone here can figure out how it operates, as my knowledge of Javascript is much less than Asm or C/C++.
Maximus
July 26th, 2006, 04:31
Well,
* it takes each char of the string (x.charCodeAt(p++)) and sub '0' from it;
* it uses such result as index in t[];
* the result in t[] is shifted left by s (0 first time);
* if s!=0 add to r string a char: 165^w&0xFF and then
** w>>=8, s-=2
** else s=6
basically,
r+=String.fromCharCode(165^w&255); == add a char to a string
document.write(r); == fwrite to the output stream
x.charCodeAt(p++) == x[p++] (where x is a char *)
j=Math.ceil(l/b) == ((int)(l/b))+1
Math.min(l,b) == min(l,b)
cr.ap
July 26th, 2006, 05:23
input >> base64decode >> XOR 165 >> html