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# aid

The ISO 7816-4 application identifiers of the Smart Card.

```
var aid: Data? { get }
```

## Discussion

This value is specified in the Smart Card token extension’s `NSExtensionAttributes` property list by the `com.apple.ctk.aid` attribute. If this attribute specifies multiple AIDs, this parameter represents the application identifier found on the card that is already preselected.  If the `com.apple.ctk.aid` attribute is not present, no application is automatically preselected and the value of this property is `nil`.

For more information, see [App Extension Keys](https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/AppExtensionKeys.html#//apple_ref/doc/uid/TP40014212) in [Information Property List Key Reference](https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Introduction/Introduction.html#//apple_ref/doc/uid/TP40009247).

---

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