AID in Cards: EMV Transaction Flow (Part-2.1)
What is AID?
The Application Identifier (AID) refers to a unique identifier that is used to select a specific application on the card. The AID is typically a hexadecimal value that helps identify the application or service provider associated with the card.
The AID serves as a way to differentiate between multiple applications that may be present on the NFC card. Each application has its own unique AID assigned to it, allowing the Soft POS application to communicate with the desired application during the transaction.
AID has two parts RID(Registered Application Provider Identifier) and PIX( Proprietary Application Identifier).
For example, the AID of the Mastercard PS: A0000000041010, where RID = A000000004; PIX = 1010. I.e., the identifier belongs to the Mastercard product, Mastercard PS. Or, the AID of the Mastercard PS is A0000000043060, where RID = A000000004; PIX = 3060. I.e., the identifier belongs to the Maestro product, Mastercard PS. The AID’s of all payment systems are based on the same principle.
On the card, the AID can be located in tag 4F (AID itself) or 84 (Dedicated File (DF) Name). Minimum length of AID = 5 bytes, the maximum length = 16 bytes. That means, in particular, that the maximum number of characters in the AID, that the software of the device (POS, АТМ, or other) has to be able to process, is 32.
On the card, the AID can be located in tag 4F (AID itself) or 84 (Dedicated File (DF) Name). Minimum length of AID = 5 bytes, the maximum length = 16 bytes. That means, in particular, that the maximum number of characters in the AID, that the software of the device (POS, АТМ, or other) has to be able to process, is 32.
In turn, the list of all supported AID’s is stored in the device’s configuration. It is one of the things that determine the capability of its work with one or another card. The selection of an application through the List of AID`s consists in sending of a request (SELECT command) from a device to a card indicating a specific AID in the «Data» field.
