An authentication server contains a database of user IDs, passwords, and other information such as IP addresses and approved services.
It monitors connections from client systems over a computer network . Passwords are not saved in clear text, only their image is saved under a one-way function , such as Message Digest Algorithm 5 (MD5) in Windows systems or Crypt (a data encryption standard method) in Unix . When a user tries to log on to a device that uses an authentication server to evaluate the logon data, that device encrypts the user ID and password as a file and sends them to the authentication server for verification. This compares with the stored password. If they match, the saved data of the checked user is released. The disadvantage of authentication servers is that they only work with systems that crawl the server when a user logs on.
- crypt (Unix) in the English Wikipedia