Security Challenges

Authentication:: How to perform authentication without sending user name and password over the Internet? How do I know, when I connect to a site, who operates the site? Is www.walmart.com the site of Wal-Mart?
Confidentiality:: How to protect the privacy of communication? How to ensure that messages have not been modified between the sender and the receiver? Is the document that I received the same as the document on the server?
Authorization:: How to ensure that the documents are read by authorized people? Or the applet is executed only by authorized users?