---
title: identifier
framework: accessorytransportextension
role: symbol
role_heading: Instance Property
path: accessorytransportextension/securitymessage/identifier
---

# identifier

An optional Bluetooth identifier that the system uses to derive HPKE keys.

## Declaration

```swift
let identifier: String?
```

## Discussion

Discussion The system provides this identifier when delivering SecurityMessage.KeyType.encapsulatedKey to your extension. Forward it to your accessory for key derivation.