I have learned a lot on access badge rfid but something there is not much in the google world.
I know Mifare Desfire ev1 works like apps with several keys for each app. As of now it is the most secure.
What I am wondering is for an access control system the security of the desfire isnt taken in to account if using the wiegand format (from reader to controller)?
As I understand it the reader would need to know the encryted keys to use authentication tokens. The MT15 that I am really looking at I cant find anything about adding encryption keys. I couldnt find anything on any readers about changing/updating encryption keys on the reader.
How can mifare desfire be used with the best security when it comes to access control systems?
Turns out the MT15 has a standard encryption key they use and also put in their badges. If you want to change it you have to work with them to do so (I called).
Also have to get special keys that use the new encryption key. Elias answer was exactly right you just cant do it yourself with that reader.