edwards.js

'use strict';

var curve = require('../curve');
var elliptic = require('../../elliptic');
var bn = require('bn.js');
var inherits = require('inherits');
var Base = curve.base;

var assert = elliptic.utils.assert;

function EdwardsCurve(conf) {
  // NOTE: Important as we are creating point in Base.call()
  this.twisted = (conf.a | 0) !== 1;
  this.mOneA = this.twisted && (conf.a | 0) === -1;
  this.extended = this.mOneA;

  Base.call(this, 'edwards', conf);

  this.a = new bn(conf.a, 16).mod(this.red.m).toRed(this.red);
  this.c = new bn(conf.c, 16).toRed(this.red);
  this.c2 = this.c.redSqr();
  this.d = new bn(conf.d, 16).toRed(this.red);
  this.dd = this.d.redAdd(this.d);

  assert(!this.twisted || this.c.fromRed().cmpn(1) === 0);
  this.oneC = (conf.c | 0) === 1;
}
inherits(EdwardsCurve, Base);
module.exports = EdwardsCurve;

EdwardsCurve.prototype._mulA = function _mulA(num) {
  if (this.mOneA)
    return num.redNeg();
  else
    return this.a.redMul(num);
};

EdwardsCurve.prototype._mulC = function _mulC(num) {
  if (this.oneC)
    return num;
  else
    return this.c.redMul(num);
};

// Just for compatibility with Short curve
EdwardsCurve.prototype.jpoint = function jpoint(x, y, z, t) {
  return this.point(x, y, z, t);
};

EdwardsCurve.prototype.pointFromX = function pointFromX(odd, x) {
  x = new bn(x, 16);
  if (!x.red)
    x = x.toRed(this.red);

  var x2 = x.redSqr();
  var rhs = this.c2.redSub(this.a.redMul(x2));
  var lhs = this.one.redSub(this.c2.redMul(this.d).redMul(x2));

  var y = rhs.redMul(lhs.redInvm()).redSqrt();
  var isOdd = y.fromRed().isOdd();
  if (odd && !isOdd || !odd && isOdd)
    y = y.redNeg();

  return this.point(x, y, curve.one);
};

EdwardsCurve.prototype.validate = function validate(point) {
  if (point.isInfinity())
    return true;

  // Curve: A * X^2 + Y^2 = C^2 * (1 + D * X^2 * Y^2)
  point.normalize();

  var x2 = point.x.redSqr();
  var y2 = point.y.redSqr();
  var lhs = x2.redMul(this.a).redAdd(y2);
  var rhs = this.c2.redMul(this.one.redAdd(this.d.redMul(x2).redMul(y2)));

  return lhs.cmp(rhs) === 0;
};

function Point(curve, x, y, z, t) {
  Base.BasePoint.call(this, curve, 'projective');
  if (x === null && y === null && z === null) {
    this.x = this.curve.zero;
    this.y = this.curve.one;
    this.z = this.curve.one;
    this.t = this.curve.zero;
    this.zOne = true;
  } else {
    this.x = new bn(x, 16);
    this.y = new bn(y, 16);
    this.z = z ? new bn(z, 16) : this.curve.one;
    this.t = t && new bn(t, 16);
    if (!this.x.red)
      this.x = this.x.toRed(this.curve.red);
    if (!this.y.red)
      this.y = this.y.toRed(this.curve.red);
    if (!this.z.red)
      this.z = this.z.toRed(this.curve.red);
    if (this.t && !this.t.red)
      this.t = this.t.toRed(this.curve.red);
    this.zOne = this.z === this.curve.one;

    // Use extended coordinates
    if (this.curve.extended && !this.t) {
      this.t = this.x.redMul(this.y);
      if (!this.zOne)
        this.t = this.t.redMul(this.z.redInvm());
    }
  }
}
inherits(Point, Base.BasePoint);

EdwardsCurve.prototype.pointFromJSON = function pointFromJSON(obj) {
  return Point.fromJSON(this, obj);
};

EdwardsCurve.prototype.point = function point(x, y, z, t) {
  return new Point(this, x, y, z, t);
};

Point.fromJSON = function fromJSON(curve, obj) {
  return new Point(curve, obj[0], obj[1], obj[2]);
};

Point.prototype.inspect = function inspect() {
  if (this.isInfinity())
    return '<EC Point Infinity>';
  return '<EC Point x: ' + this.x.fromRed().toString(16, 2) +
      ' y: ' + this.y.fromRed().toString(16, 2) +
      ' z: ' + this.z.fromRed().toString(16, 2) + '>';
};

Point.prototype.isInfinity = function isInfinity() {
  // XXX This code assumes that zero is always zero in red
  return this.x.cmpn(0) === 0 &&
         this.y.cmp(this.z) === 0;
};

Point.prototype._extDbl = function _extDbl() {
  // hyperelliptic.org/EFD/g1p/auto-twisted-extended-1.html
  //     #doubling-dbl-2008-hwcd
  // 4M + 4S

  // A = X1^2
  var a = this.x.redSqr();
  // B = Y1^2
  var b = this.y.redSqr();
  // C = 2 * Z1^2
  var c = this.z.redSqr();
  c = c.redIAdd(c);
  // D = a * A
  var d = this.curve._mulA(a);
  // E = (X1 + Y1)^2 - A - B
  var e = this.x.redAdd(this.y).redSqr().redISub(a).redISub(b);
  // G = D + B
  var g = d.redAdd(b);
  // F = G - C
  var f = g.redSub(c);
  // H = D - B
  var h = d.redSub(b);
  // X3 = E * F
  var nx = e.redMul(f);
  // Y3 = G * H
  var ny = g.redMul(h);
  // T3 = E * H
  var nt = e.redMul(h);
  // Z3 = F * G
  var nz = f.redMul(g);
  return this.curve.point(nx, ny, nz, nt);
};

Point.prototype._projDbl = function _projDbl() {
  // hyperelliptic.org/EFD/g1p/auto-twisted-projective.html
  //     #doubling-dbl-2008-bbjlp
  //     #doubling-dbl-2007-bl
  // and others
  // Generally 3M + 4S or 2M + 4S

  // B = (X1 + Y1)^2
  var b = this.x.redAdd(this.y).redSqr();
  // C = X1^2
  var c = this.x.redSqr();
  // D = Y1^2
  var d = this.y.redSqr();

  var nx;
  var ny;
  var nz;
  if (this.curve.twisted) {
    // E = a * C
    var e = this.curve._mulA(c);
    // F = E + D
    var f = e.redAdd(d);
    if (this.zOne) {
      // X3 = (B - C - D) * (F - 2)
      nx = b.redSub(c).redSub(d).redMul(f.redSub(this.curve.two));
      // Y3 = F * (E - D)
      ny = f.redMul(e.redSub(d));
      // Z3 = F^2 - 2 * F
      nz = f.redSqr().redSub(f).redSub(f);
    } else {
      // H = Z1^2
      var h = this.z.redSqr();
      // J = F - 2 * H
      var j = f.redSub(h).redISub(h);
      // X3 = (B-C-D)*J
      nx = b.redSub(c).redISub(d).redMul(j);
      // Y3 = F * (E - D)
      ny = f.redMul(e.redSub(d));
      // Z3 = F * J
      nz = f.redMul(j);
    }
  } else {
    // E = C + D
    var e = c.redAdd(d);
    // H = (c * Z1)^2
    var h = this.curve._mulC(this.c.redMul(this.z)).redSqr();
    // J = E - 2 * H
    var j = e.redSub(h).redSub(h);
    // X3 = c * (B - E) * J
    nx = this.curve._mulC(b.redISub(e)).redMul(j);
    // Y3 = c * E * (C - D)
    ny = this.curve._mulC(e).redMul(c.redISub(d));
    // Z3 = E * J
    nz = e.redMul(j);
  }
  return this.curve.point(nx, ny, nz);
};

Point.prototype.dbl = function dbl() {
  if (this.isInfinity())
    return this;

  // Double in extended coordinates
  if (this.curve.extended)
    return this._extDbl();
  else
    return this._projDbl();
};

Point.prototype._extAdd = function _extAdd(p) {
  // hyperelliptic.org/EFD/g1p/auto-twisted-extended-1.html
  //     #addition-add-2008-hwcd-3
  // 8M

  // A = (Y1 - X1) * (Y2 - X2)
  var a = this.y.redSub(this.x).redMul(p.y.redSub(p.x));
  // B = (Y1 + X1) * (Y2 + X2)
  var b = this.y.redAdd(this.x).redMul(p.y.redAdd(p.x));
  // C = T1 * k * T2
  var c = this.t.redMul(this.curve.dd).redMul(p.t);
  // D = Z1 * 2 * Z2
  var d = this.z.redMul(p.z.redAdd(p.z));
  // E = B - A
  var e = b.redSub(a);
  // F = D - C
  var f = d.redSub(c);
  // G = D + C
  var g = d.redAdd(c);
  // H = B + A
  var h = b.redAdd(a);
  // X3 = E * F
  var nx = e.redMul(f);
  // Y3 = G * H
  var ny = g.redMul(h);
  // T3 = E * H
  var nt = e.redMul(h);
  // Z3 = F * G
  var nz = f.redMul(g);
  return this.curve.point(nx, ny, nz, nt);
};

Point.prototype._projAdd = function _projAdd(p) {
  // hyperelliptic.org/EFD/g1p/auto-twisted-projective.html
  //     #addition-add-2008-bbjlp
  //     #addition-add-2007-bl
  // 10M + 1S

  // A = Z1 * Z2
  var a = this.z.redMul(p.z);
  // B = A^2
  var b = a.redSqr();
  // C = X1 * X2
  var c = this.x.redMul(p.x);
  // D = Y1 * Y2
  var d = this.y.redMul(p.y);
  // E = d * C * D
  var e = this.curve.d.redMul(c).redMul(d);
  // F = B - E
  var f = b.redSub(e);
  // G = B + E
  var g = b.redAdd(e);
  // X3 = A * F * ((X1 + Y1) * (X2 + Y2) - C - D)
  var tmp = this.x.redAdd(this.y).redMul(p.x.redAdd(p.y)).redISub(c).redISub(d);
  var nx = a.redMul(f).redMul(tmp);
  var ny;
  var nz;
  if (this.curve.twisted) {
    // Y3 = A * G * (D - a * C)
    ny = a.redMul(g).redMul(d.redSub(this.curve._mulA(c)));
    // Z3 = F * G
    nz = f.redMul(g);
  } else {
    // Y3 = A * G * (D - C)
    ny = a.redMul(g).redMul(d.redSub(c));
    // Z3 = c * F * G
    nz = this.curve._mulC(f).redMul(g);
  }
  return this.curve.point(nx, ny, nz);
};

Point.prototype.add = function add(p) {
  if (this.isInfinity())
    return p;
  if (p.isInfinity())
    return this;

  if (this.curve.extended)
    return this._extAdd(p);
  else
    return this._projAdd(p);
};

Point.prototype.mul = function mul(k) {
  if (this.precomputed && this.precomputed.doubles)
    return this.curve._fixedNafMul(this, k);
  else
    return this.curve._wnafMul(this, k);
};

Point.prototype.mulAdd = function mulAdd(k1, p, k2) {
  return this.curve._wnafMulAdd(1, [ this, p ], [ k1, k2 ], 2);
};

Point.prototype.normalize = function normalize() {
  if (this.zOne)
    return this;

  // Normalize coordinates
  var zi = this.z.redInvm();
  this.x = this.x.redMul(zi);
  this.y = this.y.redMul(zi);
  if (this.t)
    this.t = this.t.redMul(zi);
  this.z = this.curve.one;
  this.zOne = true;
  return this;
};

Point.prototype.neg = function neg() {
  return this.curve.point(this.x.redNeg(),
                          this.y,
                          this.z,
                          this.t && this.t.redNeg());
};

Point.prototype.getX = function getX() {
  this.normalize();
  return this.x.fromRed();
};

Point.prototype.getY = function getY() {
  this.normalize();
  return this.y.fromRed();
};

// Compatibility with BaseCurve
Point.prototype.toP = Point.prototype.normalize;
Point.prototype.mixedAdd = Point.prototype.add;