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Filename : index.js
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'use strict';

var BN = require('bn.js');
var HmacDRBG = require('hmac-drbg');
var utils = require('../utils');
var curves = require('../curves');
var rand = require('brorand');
var assert = utils.assert;

var KeyPair = require('./key');
var Signature = require('./signature');

function EC(options) {
  if (!(this instanceof EC))
    return new EC(options);

  // Shortcut `elliptic.ec(curve-name)`
  if (typeof options === 'string') {
    assert(Object.prototype.hasOwnProperty.call(curves, options),
      'Unknown curve ' + options);

    options = curves[options];
  }

  // Shortcut for `elliptic.ec(elliptic.curves.curveName)`
  if (options instanceof curves.PresetCurve)
    options = { curve: options };

  this.curve = options.curve.curve;
  this.n = this.curve.n;
  this.nh = this.n.ushrn(1);
  this.g = this.curve.g;

  // Point on curve
  this.g = options.curve.g;
  this.g.precompute(options.curve.n.bitLength() + 1);

  // Hash for function for DRBG
  this.hash = options.hash || options.curve.hash;
}
module.exports = EC;

EC.prototype.keyPair = function keyPair(options) {
  return new KeyPair(this, options);
};

EC.prototype.keyFromPrivate = function keyFromPrivate(priv, enc) {
  return KeyPair.fromPrivate(this, priv, enc);
};

EC.prototype.keyFromPublic = function keyFromPublic(pub, enc) {
  return KeyPair.fromPublic(this, pub, enc);
};

EC.prototype.genKeyPair = function genKeyPair(options) {
  if (!options)
    options = {};

  // Instantiate Hmac_DRBG
  var drbg = new HmacDRBG({
    hash: this.hash,
    pers: options.pers,
    persEnc: options.persEnc || 'utf8',
    entropy: options.entropy || rand(this.hash.hmacStrength),
    entropyEnc: options.entropy && options.entropyEnc || 'utf8',
    nonce: this.n.toArray(),
  });

  var bytes = this.n.byteLength();
  var ns2 = this.n.sub(new BN(2));
  for (;;) {
    var priv = new BN(drbg.generate(bytes));
    if (priv.cmp(ns2) > 0)
      continue;

    priv.iaddn(1);
    return this.keyFromPrivate(priv);
  }
};

EC.prototype._truncateToN = function _truncateToN(msg, truncOnly) {
  var delta = msg.byteLength() * 8 - this.n.bitLength();
  if (delta > 0)
    msg = msg.ushrn(delta);
  if (!truncOnly && msg.cmp(this.n) >= 0)
    return msg.sub(this.n);
  else
    return msg;
};

EC.prototype.sign = function sign(msg, key, enc, options) {
  if (typeof enc === 'object') {
    options = enc;
    enc = null;
  }
  if (!options)
    options = {};

  key = this.keyFromPrivate(key, enc);
  msg = this._truncateToN(new BN(msg, 16));

  // Zero-extend key to provide enough entropy
  var bytes = this.n.byteLength();
  var bkey = key.getPrivate().toArray('be', bytes);

  // Zero-extend nonce to have the same byte size as N
  var nonce = msg.toArray('be', bytes);

  // Instantiate Hmac_DRBG
  var drbg = new HmacDRBG({
    hash: this.hash,
    entropy: bkey,
    nonce: nonce,
    pers: options.pers,
    persEnc: options.persEnc || 'utf8',
  });

  // Number of bytes to generate
  var ns1 = this.n.sub(new BN(1));

  for (var iter = 0; ; iter++) {
    var k = options.k ?
      options.k(iter) :
      new BN(drbg.generate(this.n.byteLength()));
    k = this._truncateToN(k, true);
    if (k.cmpn(1) <= 0 || k.cmp(ns1) >= 0)
      continue;

    var kp = this.g.mul(k);
    if (kp.isInfinity())
      continue;

    var kpX = kp.getX();
    var r = kpX.umod(this.n);
    if (r.cmpn(0) === 0)
      continue;

    var s = k.invm(this.n).mul(r.mul(key.getPrivate()).iadd(msg));
    s = s.umod(this.n);
    if (s.cmpn(0) === 0)
      continue;

    var recoveryParam = (kp.getY().isOdd() ? 1 : 0) |
                        (kpX.cmp(r) !== 0 ? 2 : 0);

    // Use complement of `s`, if it is > `n / 2`
    if (options.canonical && s.cmp(this.nh) > 0) {
      s = this.n.sub(s);
      recoveryParam ^= 1;
    }

    return new Signature({ r: r, s: s, recoveryParam: recoveryParam });
  }
};

EC.prototype.verify = function verify(msg, signature, key, enc) {
  msg = this._truncateToN(new BN(msg, 16));
  key = this.keyFromPublic(key, enc);
  signature = new Signature(signature, 'hex');

  // Perform primitive values validation
  var r = signature.r;
  var s = signature.s;
  if (r.cmpn(1) < 0 || r.cmp(this.n) >= 0)
    return false;
  if (s.cmpn(1) < 0 || s.cmp(this.n) >= 0)
    return false;

  // Validate signature
  var sinv = s.invm(this.n);
  var u1 = sinv.mul(msg).umod(this.n);
  var u2 = sinv.mul(r).umod(this.n);
  var p;

  if (!this.curve._maxwellTrick) {
    p = this.g.mulAdd(u1, key.getPublic(), u2);
    if (p.isInfinity())
      return false;

    return p.getX().umod(this.n).cmp(r) === 0;
  }

  // NOTE: Greg Maxwell's trick, inspired by:
  // https://git.io/vad3K

  p = this.g.jmulAdd(u1, key.getPublic(), u2);
  if (p.isInfinity())
    return false;

  // Compare `p.x` of Jacobian point with `r`,
  // this will do `p.x == r * p.z^2` instead of multiplying `p.x` by the
  // inverse of `p.z^2`
  return p.eqXToP(r);
};

EC.prototype.recoverPubKey = function(msg, signature, j, enc) {
  assert((3 & j) === j, 'The recovery param is more than two bits');
  signature = new Signature(signature, enc);

  var n = this.n;
  var e = new BN(msg);
  var r = signature.r;
  var s = signature.s;

  // A set LSB signifies that the y-coordinate is odd
  var isYOdd = j & 1;
  var isSecondKey = j >> 1;
  if (r.cmp(this.curve.p.umod(this.curve.n)) >= 0 && isSecondKey)
    throw new Error('Unable to find sencond key candinate');

  // 1.1. Let x = r + jn.
  if (isSecondKey)
    r = this.curve.pointFromX(r.add(this.curve.n), isYOdd);
  else
    r = this.curve.pointFromX(r, isYOdd);

  var rInv = signature.r.invm(n);
  var s1 = n.sub(e).mul(rInv).umod(n);
  var s2 = s.mul(rInv).umod(n);

  // 1.6.1 Compute Q = r^-1 (sR -  eG)
  //               Q = r^-1 (sR + -eG)
  return this.g.mulAdd(s1, r, s2);
};

EC.prototype.getKeyRecoveryParam = function(e, signature, Q, enc) {
  signature = new Signature(signature, enc);
  if (signature.recoveryParam !== null)
    return signature.recoveryParam;

  for (var i = 0; i < 4; i++) {
    var Qprime;
    try {
      Qprime = this.recoverPubKey(e, signature, i);
    } catch (e) {
      continue;
    }

    if (Qprime.eq(Q))
      return i;
  }
  throw new Error('Unable to find valid recovery factor');
};