So the technical requirements will be:
- Linux (Server)
- Apache (Webserver)
- php (programming language)
- SSL (encryption)
- MySQL (database)
HTML only won't cut it. (You need php to implement the database access.)
To secure the confidential data that is transferred to the web browser you can use SSL (Secure socket layers). With SSL the information transferred over the network will be encrypted.
Check
http://www.php.net for more info about php.
It's a really nice project. Have fun with it.