ellipticCurve.js

(function (exports) {

  /**
  * Dependencies 
  * - jsbn.js 
  * - jsbn2.js 
  * - prng4.js 
  * - ec.js 
  * - sec.js 
  * - rng.js
  */ 

  'use strict';

  function EllipticCurve () {
    // Get a curve using Stanford ec / sec library
    var c = getSECCurveByName('secp160k1');

    // The user's private point (key)
    this.privatePoint = null;

    // Use the Web Cryptography API to generate a random number
    this.rng = new SecureRandom();

    // Define the various points of the EC
    this.q = c.getCurve().getQ().toString();
    this.a = c.getCurve().getA().toBigInteger().toString();
    this.b = c.getCurve().getB().toBigInteger().toString();
    this.gx = c.getG().getX().toBigInteger().toString();
    this.gy = c.getG().getY().toBigInteger().toString();
    this.n = c.getN().toString();
  }

  EllipticCurve.prototype.getCurve = function () {
    return new ECCurveFp(
      new BigInteger(this.q),
      new BigInteger(this.a),
      new BigInteger(this.b)
    );
  };

  /** 
  * @return {BigInteger} 
  */
  EllipticCurve.prototype.pickRandom = function () {
    var n = new BigInteger(this.n),
    n1 = n.subtract(BigInteger.ONE),
    r = new BigInteger(n.bitLength(), this.rng);
    return r.mod(n1).add(BigInteger.ONE);
  };

  EllipticCurve.prototype.getPrivatePoint = function () {
    return (this.privatePoint = this.pickRandom().toString());
  };

  /**
  * @param {Object} curve
  * @return {Object}  
  */ 
  EllipticCurve.prototype.getG = function (curve) {
    return new ECPointFp(
      curve,
      curve.fromBigInteger(new BigInteger(this.gx)),
      curve.fromBigInteger(new BigInteger(this.gy))
    );
  };

  /** 
  * @return {Object} 
  */ 
  EllipticCurve.prototype.getPublicPoint = function () {
    var curve, G, a, P, after; 

    if (!this.privatePoint) {
      throw new Error('No can do, Chief...You need to make a private key first.');
    }

    curve = this.getCurve();
    G = this.getG(curve);
    a = new BigInteger(this.privatePoint);
    P = G.multiply(a);

    return {
      x: P.getX().toBigInteger().toString(), 
      y: P.getY().toBigInteger().toString()
    };
  };

  // Exports 

  exports.EllipticCurve = EllipticCurve; 

})(window);