Security :: Authentication For Connected User Database Links (release 11.x)

I know how to use database links in various forms, but I've been trying to think through how the authentication works for a connected user link in 11g. If I create the link like this,create public database link using 'orcl';then any user can use the link, provided they have an identical username/password in the two databases. With pre-11g passwords, it was understandable: the password was salted with the username, so the hash of the password would be the same in both databases, and I assumed that the logon through the link used some sort of IDENTIFIED BY VALUES mechanism. But in 11g, the salt will different in the two databases. So the hash will be different. And of course Oracle never stores the actual password. So I don't see how the authentication works.