It is a replacement to sending passwords over the wire. There are no viable replacements to passwords, which are really just secrets, memorized or not--short of

It is a replacement to sending passwords over the wire. There are no viable replacements to passwords, which are really just secrets, memorized or not--short of issuing secure tokens or installing high-grade optical sensors in all laptops and getting all services on the Internet to add support for those authentication methods, anyway. This is why we're still using them. Even public-key authentication isn't secure if you're storing the private key on a regular machine, and are not protecting it with a password. Getting the regular Joe to actually use certificates is difficult enough, too.