Device Integrity Verify that requests to your server come from a genuine Apple device running your unmodified app. DeviceCheck provides per-device bits for simple flags (e.g., "claimed promo offer"). App Attest uses Secure Enclave keys and Apple attestation to cryptographically prove app legitimacy on each request. Contents DCDevice (DeviceCheck Tokens) DCAppAttestService (App Attest) App Attest Key Generation App Attest Attestation Flow App Attest Assertion Flow Server Verification Guidance Error Handling Common Patterns Common Mistakes Review Checklist DCDevice (DeviceCheck Tokens) DCDevice generates a unique, ephemeral token that identifies a device. The token is sent to your server, which then communicates with Apple's servers to read or set two per-device bits. Available on iOS 11+. Token Generation import DeviceCheck func generateDeviceToken ( ) async throws -> Data { guard DCDevice . current . isSupported else { throw DeviceIntegrityError . deviceCheckUnsupported } return try await DCDevice . current . generateToken ( ) } Sending the Token to Your Server func sendTokenToServer ( _ token : Data ) async throws { let tokenString = token . base64EncodedString ( ) var request = URLRequest ( url : serverURL . appending ( path : "verify-device" ) ) request . httpMethod = "POST" request . setValue ( "application/json" , forHTTPHeaderField : "Content-Type" ) request . httpBody = try JSONEncoder ( ) . encode ( [ "device_token" : tokenString ] ) let ( _ , response ) = try await URLSession . shared . data ( for : request ) guard let httpResponse = response as ? HTTPURLResponse , httpResponse . statusCode == 200 else { throw DeviceIntegrityError . serverVerificationFailed } } Server-Side Overview Your server uses the device token to call Apple's DeviceCheck API endpoints: Endpoint Purpose https://api.devicecheck.apple.com/v1/query_two_bits Read the two bits for a device https://api.devicecheck.apple.com/v1/update_two_bits Set the two bits for a device https://api.devicecheck.apple.com/v1/validate_device_token Validate a device token without reading bits The server authenticates with a DeviceCheck private key from the Apple Developer portal, creating a signed JWT for each request. What the Two Bits Are For Apple stores two Boolean values per device per developer team. You decide what they mean. Common uses: Bit 0: Device has claimed a promotional offer. Bit 1: Device has been flagged for fraud. Bits persist across app reinstall; device reset does not clear them. You control when to reset them via the server API. DCAppAttestService (App Attest) DCAppAttestService validates that a specific instance of your app on a specific device is legitimate. It uses a hardware-backed key in the Secure Enclave to create cryptographic attestations and assertions. Available on iOS 14+. The flow has three phases: Key generation -- create a key pair in the Secure Enclave. Attestation -- Apple certifies the key belongs to a genuine Apple device running your app. Assertion -- sign server requests with the attested key to prove ongoing legitimacy. Checking Support import DeviceCheck let attestService = DCAppAttestService . shared guard attestService . isSupported else { // Fall back to DCDevice token or other risk assessment. // App Attest is not available on simulators or all device models. return } App Attest Key Generation Generate a cryptographic key pair stored in the Secure Enclave. The returned keyId is a string identifier you persist (e.g., in Keychain) for later attestation and assertion calls. import DeviceCheck actor AppAttestManager { private let service = DCAppAttestService . shared private var keyId : String ? /// Generate and persist a key pair for App Attest. func generateKeyIfNeeded ( ) async throws -> String { if let existingKeyId = loadKeyIdFromKeychain ( ) { self . keyId = existingKeyId return existingKeyId } let newKeyId = try await service . generateKey ( ) saveKeyIdToKeychain ( newKeyId ) self . keyId = newKeyId return newKeyId } // MARK: - Keychain helpers (simplified) private func saveKeyIdToKeychain ( _ keyId : String ) { let data = Data ( keyId . utf8 ) let query : [ String : Any ] = [ kSecClass as String : kSecClassGenericPassword , kSecAttrAccount as String : "app-attest-key-id" , kSecAttrService as String : Bundle . main . bundleIdentifier ?? "" , kSecValueData as String : data , kSecAttrAccessible as String : kSecAttrAccessibleAfterFirstUnlockThisDeviceOnly ] SecItemDelete ( query as CFDictionary ) // Remove old if exists SecItemAdd ( query as CFDictionary , nil ) } private func loadKeyIdFromKeychain ( ) -> String ? { let query : [ String : Any ] = [ kSecClass as String : kSecClassGenericPassword , kSecAttrAccount as String : "app-attest-key-id" , kSecAttrService as String : Bundle . main . bundleIdentifier ?? "" , kSecReturnData as String : true , kSecMatchLimit as String : kSecMatchLimitOne ] var result : AnyObject ? let status = SecItemCopyMatching ( query as CFDictionary , & result ) guard status == errSecSuccess , let data = result as ? Data else { return nil } return String ( data : data , encoding : . utf8 ) } } Important: Generate the key once and persist the keyId . Generating a new key invalidates any previous attestation. App Attest Attestation Flow Attestation proves that the key was generated on a genuine Apple device running your unmodified app. You perform attestation once per key, then store the attestation object on your server. Client-Side Attestation import DeviceCheck import CryptoKit extension AppAttestManager { /// Attest the key with Apple. Send the attestation object to your server. func attestKey ( ) async throws -> Data { guard let keyId else { throw DeviceIntegrityError . keyNotGenerated } // 1. Request a one-time challenge from your server let challenge = try await fetchServerChallenge ( ) // 2. Hash the challenge (Apple requires a SHA-256 hash) let challengeHash = Data ( SHA256 . hash ( data : challenge ) ) // 3. Ask Apple to attest the key let attestation = try await service . attestKey ( keyId , clientDataHash : challengeHash ) // 4. Send the attestation object to your server for verification try await sendAttestationToServer ( keyId : keyId , attestation : attestation , challenge : challenge ) return attestation } private func fetchServerChallenge ( ) async throws -> Data { let url = serverURL . appending ( path : "attest/challenge" ) let ( data , _ ) = try await URLSession . shared . data ( from : url ) return data } private func sendAttestationToServer ( keyId : String , attestation : Data , challenge : Data ) async throws { var request = URLRequest ( url : serverURL . appending ( path : "attest/verify" ) ) request . httpMethod = "POST" request . setValue ( "application/json" , forHTTPHeaderField : "Content-Type" ) let payload : [ String : String ] = [ "key_id" : keyId , "attestation" : attestation . base64EncodedString ( ) , "challenge" : challenge . base64EncodedString ( ) ] request . httpBody = try JSONEncoder ( ) . encode ( payload ) let ( _ , response ) = try await URLSession . shared . data ( for : request ) guard let httpResponse = response as ? HTTPURLResponse , httpResponse . statusCode == 200 else { throw DeviceIntegrityError . attestationVerificationFailed } } } Server-Side Attestation Verification Your server must: Verify the attestation object is a valid CBOR-encoded structure. Extract the certificate chain and validate it against Apple's App Attest root CA. Verify the nonce in the attestation matches SHA256(challenge) . Extract and store the public key and receipt for future assertion verification. See Validating apps that connect to your server for the full server verification algorithm. App Attest Assertion Flow After attestation, use assertions to sign individual requests. Each assertion proves the request came from the attested app instance. Client-Side Assertion import DeviceCheck import CryptoKit extension AppAttestManager { /// Generate an assertion to accompany a server request. /// - Parameter requestData: The request payload to sign (e.g., JSON body). /// - Returns: The assertion data to include with the request. func generateAssertion ( for requestData : Data ) async throws -> Data { guard let keyId else { throw DeviceIntegrityError . keyNotGenerated } // Hash the request data -- the server will verify this matches let clientDataHash = Data ( SHA256 . hash ( data : requestData ) ) return try await service . generateAssertion ( keyId , clientDataHash : clientDataHash ) } } Using Assertions in Network Requests extension AppAttestManager { /// Perform an attested API request. func makeAttestedRequest ( to url : URL , method : String = "POST" , body : Data ) async throws -> ( Data , URLResponse ) { let assertion = try await generateAssertion ( for : body ) var request = URLRequest ( url : url ) request . httpMethod = method request . setValue ( "application/json" , forHTTPHeaderField : "Content-Type" ) request . setValue ( assertion . base64EncodedString ( ) , forHTTPHeaderField : "X-App-Assertion" ) request . httpBody = body return try await URLSession . shared . data ( for : request ) } } Server-Side Assertion Verification Your server must: Decode the assertion (CBOR). Verify the authenticator data, including the counter (must be greater than the stored counter). Verify the signature using the stored public key from attestation. Confirm the clientDataHash matches the SHA-256 of the received request body. Update the stored counter to prevent replay attacks. Server Verification Guidance Attestation vs. Assertion Phase When What It Proves Frequency Attestation After key generation The key lives on a genuine Apple device running your unmodified app Once per key Assertion With each sensitive request The request came from the attested app instance Per request Recommended Server Architecture Challenge endpoint -- generate a random nonce, store it server-side with a short TTL (e.g., 5 minutes). Attestation verification endpoint -- validate the attestation object, store the public key and receipt keyed by keyId . Assertion verification middleware -- verify assertions on sensitive endpoints (purchases, account changes). Risk Assessment Combine App Attest with fraud risk assessment for defense in depth. App Attest alone does not guarantee the user is not abusing the app -- it confirms the app is genuine. Error Handling DCError Codes import DeviceCheck func handleAttestError ( _ error : Error ) { if let dcError = error as ? DCError { switch dcError . code { case . unknownSystemFailure : // Transient system error -- retry with exponential backoff break case . featureUnsupported : // Device or OS does not support this feature // Fall back to alternative verification break case . invalidKey : // Key is corrupted or was invalidated // Generate a new key and re-attest break case . invalidInput : // The clientDataHash or keyId was malformed break case . serverUnavailable : // Apple's attestation server is unreachable -- retry later break @unknown default : break } } } Retry Strategy extension AppAttestManager { func attestKeyWithRetry ( maxAttempts : Int = 3 ) async throws -> Data { var lastError : Error ? for attempt in 0 ..< maxAttempts { do { return try await attestKey ( ) } catch let error as DCError where error . code == . serverUnavailable { lastError = error let delay = UInt64 ( pow ( 2.0 , Double ( attempt ) ) ) * 1_000_000_000 try await Task . sleep ( nanoseconds : delay ) } catch { throw error // Non-retryable errors propagate immediately } } throw lastError ?? DeviceIntegrityError . attestationFailed } } Handling Invalidated Keys If attestKey returns DCError.invalidKey , the Secure Enclave key has been invalidated (e.g., OS update, Secure Enclave reset). Delete the stored keyId from Keychain and generate a new key: extension AppAttestManager { func handleInvalidKey ( ) async throws -> String { deleteKeyIdFromKeychain ( ) keyId = nil return try await generateKeyIfNeeded ( ) } private func deleteKeyIdFromKeychain ( ) { let query : [ String : Any ] = [ kSecClass as String : kSecClassGenericPassword , kSecAttrAccount as String : "app-attest-key-id" , kSecAttrService as String : Bundle . main . bundleIdentifier ?? "" ] SecItemDelete ( query as CFDictionary ) } } Common Patterns Full Integration Manager Combine the patterns above into a single actor that manages the full lifecycle: Check isSupported and fall back to DCDevice tokens on unsupported devices. Call generateKeyIfNeeded() on launch to create or load the persisted key. Call attestKeyWithRetry() once after key generation. Use generateAssertion(for:) on each sensitive server request. Handle DCError.invalidKey by regenerating and re-attesting. Gradual Rollout Apple recommends a gradual rollout. Gate App Attest behind a remote feature flag and fall back to DCDevice tokens on unsupported devices. Environment Entitlement Set the App Attest environment in your entitlements file. Use development during testing and production for App Store builds: < key
com.apple.developer.devicecheck.appattest-environment </ key
< string
production </ string
When the entitlement is missing, the system uses development in debug builds and production for App Store and TestFlight builds. Error Type enum DeviceIntegrityError : Error { case deviceCheckUnsupported case keyNotGenerated case attestationFailed case attestationVerificationFailed case assertionFailed case serverVerificationFailed } Common Mistakes Generating a new key on every launch. Generate once, persist the keyId in Keychain. Skipping the fallback for unsupported devices. Not all devices support App Attest. Use DCDevice tokens as fallback. Trusting attestation client-side. All verification must happen on your server. Not implementing replay protection. The server must track and increment the assertion counter. Missing the environment entitlement. Without it, debug builds use development and App Store uses production . Mismatches cause attestation failures. Not handling DCError.invalidKey . Keys can be invalidated by OS updates. Detect and regenerate. Review Checklist DCAppAttestService.isSupported checked before use; fallback to DCDevice when unsupported Key generated once and keyId persisted in Keychain Attestation performed once per key; attestation object sent to server Server validates attestation against Apple's App Attest root CA Assertions generated for each sensitive request; server verifies signature and counter DCError cases handled: .serverUnavailable with retry, .invalidKey with key regeneration App Attest environment entitlement set correctly for debug vs. production Gradual rollout considered; feature flag in place for enabling/disabling