Verify device legitimacy and app integrity using DeviceCheck (DCDevice per-device bits) and App Attest (DCAppAttestService key generation, attestation, and…
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
References
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. 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 validates the attestation object (CBOR), verifies the certificate chain against Apple's App Attest root CA, and stores the public key and receipt for future assertion verification. See references/device-integrity-patterns.md for the full server verification flow.
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 decodes the assertion (CBOR), verifies the authenticator data and counter, checks the signature against the stored public key, and confirms the clientDataHash. See references/device-integrity-patterns.md for step-by-step server verification.
Server Verification Guidance
See references/device-integrity-patterns.md for full server architecture guidance including attestation vs. assertion comparison, recommended endpoint design, and risk assessment.
Error Handling
Handle DCError codes from DeviceCheck operations. Key cases:
.serverUnavailable — retry with exponential backoff
.invalidKey — key invalidated (OS update, Secure Enclave reset); regenerate and re-attest
.featureUnsupported — fall back to DCDevice tokens
.invalidInput — malformed clientDataHash or keyId
See references/device-integrity-patterns.md for full error handling code, retry strategy, and key invalidation recovery.
Common Patterns
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.
See references/device-integrity-patterns.md for the full integration manager pattern, gradual rollout guidance, and error type definition.
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
References
Extended patterns: references/device-integrity-patterns.md
DeviceCheck framework
DCDevice
DCAppAttestService
Establishing your app's integritydon't have the plugin yet? install it then click "run inline in claude" again.