Application Priority Indicator Calculator
When a card holds several applications, the terminal has to pick one. The Application Priority Indicator is the algorithm that does the picking, and it is entirely deterministic.
How this tool works
The indicator has two parts. The first says whether the terminal and the card have any supported application in common. The second is the position, in the terminal's priority list, of the application that will be selected when they do share support. The selection is simply the first entry in the terminal's priority list that the card also supports, which makes the whole process reproducible without any negotiation over the air.
When to use it
- Predict which application a terminal will run on a card
- Debug a terminal that selects the wrong application
- Verify a card's supported application list
- Reason about terminal configuration errors
Frequently asked questions
What is the Application Priority Indicator?
A two byte value the terminal sends to the card to say which application it wants to run.
How is the selected application chosen?
The first application in the terminal's priority list that the card also supports.
Why is the cooperation level reported?
It tells the cardholder which of the two negotiation phases produced the selection.
Does the card choose its own application?
The terminal proposes and the card confirms. The card can refuse, and then the transaction moves to fallback.