# AccessoryTransportSecurity A protocol for an extension that handles cryptographic key exchange with your accessory. ``` protocol AccessoryTransportSecurity : AppExtension ``` ## Overview Implement this protocol in an extension with an `EXExtensionPointIdentifier` value of `com.apple.accessory-transport-security` to manage the key exchange process that establishes encrypted communication with your accessory. The extension runs in a separate process for security isolation and communicates with the system through the extension’s configuration object ([`AccessoryTransportSecurityConfiguration`](/documentation/AccessoryTransportExtension/AccessoryTransportSecurityConfiguration)). > Important: The system requires your app extension to have the entitlement to use this protocol. ## Add the necessary target configuration In your extension’s target properties, specify the extension point identifier: ```xml EXAppExtensionAttributes EXExtensionPointIdentifier com.apple.accessory-transport-security ``` ## Implement the extension point In your extension’s Swift code, implement the protocol and provide an event handler that responds to key exchange messages: ```swift @main struct TransportSecurity: AccessoryTransportSecurity { @AppExtensionPoint.Bind static var boundExtensionPoint: AppExtensionPoint { Identifier("com.apple.accessory-transport-security") } func accept(sessionRequest: AccessorySecuritySession.Request) -> AccessorySecuritySession.Request.Decision { return sessionRequest.accept { SecurityEventHandler(session: sessionRequest.session) } } } class SecurityEventHandler: AccessorySecuritySession.EventHandler { private var session: AccessorySecuritySession init(session: AccessorySecuritySession) { self.session = session } func messageReceived(_ message: SecurityMessage, completion: @escaping @Sendable (AccessoryMessage.Result) -> Void) { // Handle encapsulated key from system. sendKeyMaterialToAccessory(message) completion(.success) } func sessionInvalidated(error: (any Error)?) { // Clean up key material. } } ``` ## Initiate key exchange Your accessory initiates the key exchange by generating a public-private key pair and sending the public key to the system. Choose [`SecurityMessage.CipherSuite.xWing`](/documentation/AccessoryTransportExtension/SecurityMessage/CipherSuite-swift.enum/xWing) for post-quantum security or [`SecurityMessage.CipherSuite.p256`](/documentation/AccessoryTransportExtension/SecurityMessage/CipherSuite-swift.enum/p256) as a fallback: ```swift // Generate key pair. let privateKey = try XWingMLKEM768X25519.PrivateKey() let publicKey = privateKey.publicKey.rawRepresentation // Send public key to system. let message = SecurityMessage( keyType: .publicKey, cipherSuite: .xWing, version: .version1, key: publicKey, supportedTransports: [.bluetooth] ) try session.sendSecurityMessage(message) ``` The system generates cryptographic key material and delivers it to your extension by calling [`messageReceived(_:completion:)`](/documentation/AccessoryTransportExtension/AccessorySecuritySession/EventHandler/messageReceived(_:completion:)) with a [`SecurityMessage`](/documentation/AccessoryTransportExtension/SecurityMessage) containing [`SecurityMessage.KeyType.encapsulatedKey`](/documentation/AccessoryTransportExtension/SecurityMessage/KeyType-swift.enum/encapsulatedKey). Forward this key material to your accessory via Bluetooth and call the completion handler with the transmission result. For more information, see [Receiving iOS notifications on an accessory](/documentation/AccessoryTransportExtension/receiving-ios-notifications-on-an-accessory). ## Topics ### Accepting session requests [`accept(sessionRequest:)`](/documentation/AccessoryTransportExtension/AccessoryTransportSecurity/accept(sessionRequest:)) Evaluates incoming security session requests for an accessory. ## Relationships ### Inherits From [`AppExtension`](/documentation/ExtensionFoundation/AppExtension) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)