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

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:

https://api.devicecheck.apple.com/v1/query_two_bits

https://api.devicecheck.apple.com/v1/update_two_bits

https://api.devicecheck.apple.com/v1/validate_device_token

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

The flow has three phases:

1. Key generation -- create a key pair in the Secure Enclave.
2. Attestation -- Apple certifies the key belongs to a genuine Apple device running your app.
3. 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

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

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

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

• .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

production

<key>com.apple.developer.devicecheck.appattest-environment</key>
<string>production</string>

When the entitlement is missing, the system uses

development

production

See references/device-integrity-patterns.md for the full integration manager pattern, gradual rollout guidance, and error type definition.

Common Mistakes

1. Generating a new key on every launch. Generate once, persist the

   keyId

   in Keychain.
2. Skipping the fallback for unsupported devices. Not all devices support App Attest. Use

   DCDevice

   tokens as fallback.
3. Trusting attestation client-side. All verification must happen on your server.
4. Not implementing replay protection. The server must track and increment the assertion counter.
5. Missing the environment entitlement. Without it, debug builds use

   development

   and App Store uses

   production

   . Mismatches cause attestation failures.
6. 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 integrity