---
title: "Secure your apps with App Attest"
description: "Use DeviceCheck App Attest to verify genuine Apple hardware, detect modified app builds, secure server payloads, and feed fraud signals into risk assessment."
shoutout: "Unofficial, made with love by Superwall - the best way to monetize your apps."
category: "Privacy & Security"
---

# Secure your apps with App Attest


[Watch on Apple Developer](https://developer.apple.com/videos/play/wwdc2026/201/)

Use DeviceCheck App Attest to verify genuine Apple hardware, detect modified app builds, secure server payloads, and feed fraud signals into risk assessment.

## TL;DR

- App Attest protects server workflows from modified clients by proving an app key was generated for your app on genuine Apple hardware and by surfacing app identity signals.
- Adopt the flow server-first: generate a Secure Enclave-bound key, attest it with a server challenge, validate and store the attestation on your server, then use assertions for protected requests.
- Newer platform signals include macOS 27 support, key access control validation for macOS security state, and iOS 27 authenticator-data extensions for launch validation category and bundle version.
- Treat unsupported responses, new keys, assertion counter anomalies, and the receipt-based fraud metric as risk signals; avoid blocking users without broader assessment.

## Threat model and protections

App Attest is aimed at server-side fraud caused by modified copies of your app that still send valid-looking requests. Examples include a quiz app submitting falsified answers or a game client injected with cheat UI and then re-signed.

The core value is not local self-defense; it is giving your server cryptographic evidence about the app, device, and request so the server can reject or scrutinize suspicious traffic.

- App identity is represented by the relying party identifier: your Apple Developer Team Identifier plus the app bundle identifier.
- Attestations can prove the key was generated on genuine Apple hardware and expose app-related properties useful for detecting tampering.
- Assertions use an already-attested key to protect subsequent payloads sent from the app to your server.
- New iOS 27 signals include launch validation category and bundle version in authenticator-data extensions.

## Availability and key generation

App Attest is supported across major Apple platforms, including macOS 27 and later, but not in every app or extension context. Gate use with the App Attest support check and consider unexpected unsupported results as one input to fraud detection.

Key generation creates a Secure Enclave-bound key pair for the app. The private key remains in the Secure Enclave, and App Attest returns a key ID derived from the public key for the app to store.

- Use one key per user for account-based apps, or one key for the app on a device; do not share keys across users.
- Store App Attest key IDs in Keychain.
- Keys survive app updates but are invalidated by app reinstall or device restore, including iCloud restore.
- Keys are per-device and do not sync across a user's devices.

### Generate a Secure Enclave-bound key

Creates an App Attest key pair and returns the key ID that should be persisted in Keychain.

```swift
import DeviceCheck

let keyID = try await DCAppAttestService.shared.generateKey()
```

## Attestation flow and server validation

Attestation should be initiated and controlled by your server. The server vends a challenge, the app calls the attestation API with the key ID and challenge hash, and the app sends the returned attestation object back to the server for validation and storage.

Your server, not the app, must validate attestations. A compromised client cannot be trusted to validate its own integrity. Perform attestation outside critical user flows when possible, retry later on failures, and use exponential backoff instead of hard-coded retry loops.

- Validate the Apple anonymized attestation format, certificate chain, nonce, key ID, and relying party identifier.
- Validate the attestation receipt, including relying party ID, attested key, and server challenge, then store the receipt for fraud metric requests.
- On macOS 27 and later, validate the key access control property, also described as the ACL Blob OID, to confirm Secure Enclave-enforced security conditions such as full security mode and System Integrity Protection.
- Unpack authenticator data according to the documentation and W3C authenticator-data model; on iOS 27 and later, inspect extensions for launch validation category and bundle version.

### Request an attestation

The client passes the key ID and a hash of server-controlled challenge data, then sends the returned attestation to the server.

```swift
import DeviceCheck

let keyId: String = ...
let clientDataHash: Data = ...
let attestation = try await DCAppAttestService.shared.attestKey(
    keyId: keyId,
    clientDataHash: clientDataHash
)
```

## Assertions for protected requests

After the server validates an attestation and stores the public key, the app can generate assertions for ongoing protected communication. Assertions are generated locally and do not require a round trip to Apple servers.

Use assertions on demand for sensitive payloads, such as authentication-related requests or premium-content access. Generating assertions performs cryptographic work, so avoid excessive generation in tight loops or high-frequency lifecycle paths.

- Embed the assertion object in the payload sent to your server.
- Validate the assertion signature with the authenticator data, server challenge, and public key from the attestation.
- Track the assertion counter per user or key on the server and require it to be strictly increasing.
- Treat steady or decreasing counters as possible replay or compromise signals.
- Handle iOS 27 authenticator-data extensions in assertions the same way as in attestations.

### Generate an assertion

Signs challenge-bound client data with the previously attested key so the server can verify the payload.

```swift
import DeviceCheck

let keyId: String = ...
let clientDataHash: Data = ...
let assertion = try await DCAppAttestService.shared.generateAssertion(
    keyId: keyId,
    clientDataHash: clientDataHash
)
```

## Pitfalls, fraud metric, and rollout guidance

Do not reject every new key for an existing user. App reinstall and device restore can legitimately invalidate a key and require key rotation, so keep prior attestations long enough to evaluate risk rather than immediately discarding them.

The fraud metric helps detect a compromised device acting as an attestation broker. It is an approximate 30-day count of unique attested keys associated with your app on a particular device, retrieved by your server from the App Attest data server using a stored attestation receipt.

- If an attestation or assertion is rejected, degrade App Attest-protected functionality gracefully and consider limited access with heightened monitoring.
- Use unsupported App Attest responses, key rotation patterns, suspicious extension values, assertion counter anomalies, and the fraud metric as inputs to a broader risk profile.
- The fraud metric response receipt contains a signature, certificate chain, receipt payload, risk metric field, not-before refresh time, and expiration time.
- Rebuild with the latest SDKs, identify flows that benefit from attestations and assertions, set up server validation and counter tracking, and integrate the fraud metric into your risk pipeline.

## Resources

- [W3C Authenticator Data](https://www.w3.org/TR/webauthn-3/#sctn-authenticator-data)
- [About System Integrity Protection on your Mac](https://support.apple.com/en-us/102149)
- [DeviceCheck](https://developer.apple.com/documentation/DeviceCheck)

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