Can someone explain the difference between an HID proximity card's decoded and undecoded outputs? My guess is that number printed on the card is an undecoded output, and it's just there to make it easier for humans to type in a number to a software application. Probably the real number is on the card as is longer or more complex format? How many digits are there and in what format (e.g., alphanumeric only).
I saw a demo on TV recently of some guy who using a home made circuit board was able to swipe any person in his vicinity's prox cards, then record that and play it back to get access through any prox reader. Pretty scary stuff, and it's obviously not a very secure architecture if they are sending out numbers in a way that doesn't use some kind of private and public key exchange.
We are thinking of using the proximity cards as part of a two factor authentication system to login to computers, which is why I would like to understand the length and structure of the number on the card. We would be using PCPROX readers.