AID (application identifier)

An Application Identifier (AID) is a unique identifier used to identify a specific application or service within a smart card or contactless payment system. It is a crucial component of contactless payment systems, allowing the system to differentiate between different applications or services that may be stored on the same card or device.

AID is a hexadecimal value that is stored in the card or device's Application Selection System File (ADF). It is usually 5 to 16 bytes in length and is structured in accordance with the International Organization for Standardization (ISO) 7816-4 standard.

In a smart card or contactless payment system, the AID is used to identify the application or service that is being accessed. When a user taps their contactless payment card or device against a payment terminal, the terminal sends a request to the card or device asking it to provide a list of available applications or services. The card or device responds with a list of AIDs associated with each application or service. The terminal then selects the appropriate AID for the desired application or service and sends a command to the card or device to initiate the transaction.

AID is a critical component of contactless payment systems, as it allows for the secure and efficient identification of applications and services. Without AID, it would be challenging to differentiate between different applications or services stored on the same card or device, making it difficult to initiate transactions securely and efficiently.

AID can also be used for a variety of other applications, such as access control, identification, and authentication. In these applications, AID is used to identify the specific application or service that is being accessed or authenticated. For example, in an access control system, AID can be used to identify the specific access control application being used to grant access to a particular location or device.

AID is a critical component of the payment ecosystem, and its correct implementation is essential to ensuring the security and efficiency of contactless payment transactions. Properly designed and implemented AID ensures that the right application or service is accessed by the payment terminal, thus avoiding any confusion and unauthorized use.

In conclusion, AID is a unique identifier used to identify specific applications or services within a smart card or contactless payment system. It plays a critical role in ensuring the security and efficiency of contactless payment transactions and is also used in other applications such as access control, identification, and authentication. Its correct implementation is essential to ensure the security and efficiency of contactless payment transactions and other applications that rely on AID.