python RSA implemention with PKCS1

Question

I got the following code in javascript for RSA implemention http://www-cs-students.stanford.edu/~tjw/jsbn/ :

 // Return the PKCS#1 RSA encryption of "text" as an even-length hex string
function RSAEncrypt(text) {  
  var m = pkcs1pad2(text,(this.n.bitLength()+7)>>3);  
  if(m == null) return null;  
  var c = this.doPublic(m);  
  if(c == null) return null;  
  var h = c.toString(16);  
  if((h.length & 1) == 0) return h; else return "0" + h;  
}  
// PKCS#1 (type 2, random) pad input string s to n bytes, and return a bigint  
function pkcs1pad2(s,n) {  
  if(n < s.length + 11) { // TODO: fix for utf-8  
    alert("Message too long for RSA");  
    return null;  
  }  
  var ba = new Array();  
  var i = s.length - 1;  
  while(i >= 0 && n > 0) {  
    var c = s.charCodeAt(i--);  
    if(c < 128) { // encode using utf-8  
      ba[--n] = c;  
    }  
    else if((c > 127) && (c < 2048)) {  
      ba[--n] = (c & 63) | 128;  
      ba[--n] = (c >> 6) | 192;  
    }  
    else {  
      ba[--n] = (c & 63) | 128;  
      ba[--n] = ((c >> 6) & 63) | 128;  
      ba[--n] = (c >> 12) | 224;  
    }  
  }  
  ba[--n] = 0;  
  var rng = new SecureRandom();  
  var x = new Array();  
  while(n > 2) { // random non-zero pad  
    x[0] = 0;  
    while(x[0] == 0) rng.nextBytes(x);  
    ba[--n] = x[0];  
  }  
  ba[--n] = 2;  
  ba[--n] = 0;  
  return new BigInteger(ba);
}  

In the snippets above, it seems that the pkcs1pad2 function is used for padding the message with some random bytes(maybe sth like 0|2|random|0 ) in front of the message.

I'm using the python rsa package ( http://stuvel.eu/rsa ) for imitating the javascript result, i'm a newbie to python world and have no idea to traslate javascript algorithm code to the python code.

Any help would be appreciated.
Jiee

Answer 1

I know it's a bit late, but in a few days I'll release a new version of my Python-RSA package. That version will include PKCS#1 v1.5 padding, so it should be compatible with your JavaScript code ;-)