function MontCurve(conf) {
  Base.call(this, 'mont', conf);

  this.a = new BN(conf.a, 16).toRed(this.red);
  this.b = new BN(conf.b, 16).toRed(this.red);
  this.i4 = new BN(4).toRed(this.red).redInvm();
  this.two = new BN(2).toRed(this.red);
  this.a24 = this.i4.redMul(this.a.redAdd(this.two));
}
Get the binary size of a string
@param {String} str
@return {Number}