You are your smartphone

Yahoo last week unveiled a novel concept: Access to your Yahoo Mail account without a password.What is a password, anyway?If you think about it, a password is a way to authenticate a person. You create a chunk of random knowledge that only you know. Later, to prove you're you, you demonstrate mastery of that knowledge. Only you would know to type "corndog658" when prompted, so obviously you're authorized for access.It's a great way to authenticate, at least until someone steals or guesses y