rsa.js

(function(){
  // Silly RSA, fun times, if you ever use this I will come to your house and
  // punch you.
  var gcd = function(a, b) {
    var t;
    while(b !== 0){
      t = b;
      b = a % t;
      a = t;
    }
    return a;
  };
 
  var modInv = function(a, b) {
    if(b === 0) {
      return [1, 0];
    } else {
      var q = Math.floor(a / b);
      var r = a % b;
      var ret = modInv(b, r);
      return [ret[1], ret[0] - q * ret[1]];
    }
  };
 
  var expMod = function(b, e, mod) {
    var result = 1;
    while(e > 0) {
      if(e % 2 === 1) {
        result = (result * b) % mod;
        e = e - 1;
      }
      e = e / 2;
      b = (b * b) % mod;
    }
    return result;
  };
 
  var isPrime = function(p){
    var a = ((Math.random() * p - 2) | 0) + 2;
    return expMod(a, p - 1, p) === 1;
  };
 
  var randPrime = function(num){
    var p = (Math.random() * num | 0);
    while(!isPrime(p) || p < 2)
      p = (Math.random() * num | 0);
    return p;
  };
 
  var KeyPair = function(){
    var p = randPrime(100);
    var q = randPrime(100);
    var n = p * q, tot = (p - 1) * (q - 1);
    var e = randPrime(tot);
    while(e > 1 && gcd(e, n) !== 1) e = randPrime(tot);
    var d = modInv(tot, e)[1];
    if(d < 0)   d = tot + d;
    if(d > tot) d = tot - d;
    this.q = q;
    this.p = p;
    this.d = d;
    this.n = n;
    this.e = e;
  };
 
  KeyPair.prototype.encrypt = function(n){
    return expMod(n, this.e, this.n);
  };
 
  KeyPair.prototype.decrypt = function(n){
    return expMod(n, this.d, this.n);
  };
 
  this.KeyPair = KeyPair;
}).call(this);