Originally Posted by
PrancingPonyGoldMember
It already IS an open SSID - the portal you sign in on only controls whether their system lets your connection go through to the public internet or not. Since it's an open network (IE, not secured with a password/WPA2 key), everyone can see everyone else's data packets. You're relying on either your own VPN or an encrypted connection to the website you're accessing for security.
The only way they could defeat that would be to give everyone a unique username and password to log in to the Wi-Fi with, which would not be practical.
You're correct it is an open SSID and data is transmitted in the open. What I should have stated more clearly is why bother with the captive portal at all if they are using MAC authentication. I.e. totally open no authentication and no encryption. Some will assert it prevents an unsophisticated user from gaining unauthorized access to the WiFi. I won't argue that so there is some limited protection of resources.
My two cents, eliminate captive portals or simply have them be a click and go on acceptable use terms. WiFi is a utility now like running water, electric power, HVAC, etc. Too many devices have issues with captive portal implementations which makes it difficult for unsophisticated users (and if it is broken enough all users) to access the WiFi.
--Jon