TrustPin App Attestation for Flutter

Prove to your API that a request comes from your genuine app on a genuine device that meets your policy. The device attests once per device key to your own TrustPin verifier, then renews a short-lived token cheaply. The token travels in the TrustPin-Attestation header, and your API or gateway verifies it.

Platform	Minimum	Evidence
iOS	15	Apple App Attest
macOS	13	Apple App Attest
Android	API 25	Android Key Attestation; Play Integrity where Google Play services exist

This package wraps the native TrustPin attestation modules (TrustPinAttestKit on iOS and macOS, cloud.trustpin:kotlin-attest on Android) and works with the trustpin_sdk pinning package, which it requires: the SDK pins its calls to your verifier.

Attestation is not runtime protection: it doesn't detect hooking, debugging, tampering, root or jailbreak. Setup, the policy, deploying the verifier and verifying tokens in your API are covered at docs.trustpin.cloud.

Installation

dependencies:
  trustpin_sdk: ^7.1.0
  trustpin_attest: ^7.1.0

Both packages must be on the same version. They wrap the native 7.1.x SDKs (TrustPinAttestKit, cloud.trustpin:kotlin-attest).

Flutter 3.44.0 or later; iOS and macOS through Swift Package Manager only. From 7.1.0 the plugin ships no podspec. Flutter 3.44 is the first stable release with Swift Package Manager on by default; if you turned it off, turn it back on:

flutter config --enable-swift-package-manager

Before you write code

• The policy: in the TrustPin console, list your app (Team ID and bundle ID, or package name and signing-certificate digests) and publish the policy.
• Your verifier: deployed and reachable from the app, and its host registered as a domain of your TrustPin project, because verifier calls are pinned. In strict mode an unregistered verifier host fails every call (VERIFIER_UNAVAILABLE) and no header is sent. It must speak contract version 2 or newer (verifier 0.2.2 or later); an older one is refused (VERIFIER_INCOMPATIBLE).
• iOS and macOS: add the App Attest capability to the Runner target. It adds the entitlement com.apple.developer.devicecheck.appattest-environment: development for builds run from Xcode, production for TestFlight and the App Store.
• Android with Play Integrity: the Google Cloud project number of the project linked in Play Console (see Configure).

Configure

Add the attestation keys to the configuration files the pinning setup reads:

iOS, macOS: TrustPin-Info.plist

<key>AttestVerifierURL</key>
<string>https://attest.example.com</string>
<key>AttestedHosts</key>
<array>
    <string>api.example.com</string>
</array>

Android: android/app/src/main/assets/trustpin.json

{
  "attest_verifier_url": "https://attest.example.com",
  "attested_hosts": ["api.example.com"]
}

Add "google_cloud_project_number" only when your policy uses Play Integrity: with a number, the app contacts Google Play services from setup on.

• The verifier URL must be https:// on a host name, without credentials, query or fragment. IP addresses are refused.
• Attested hosts: one to fifty host names, each exact or *.example.com for exactly one label. Only these hosts ever receive the header.

Or configure in code with TrustPinAttestConfiguration and setup.

Set up

Once per launch, after pinning:

import 'package:trustpin_attest/trustpin_attest.dart';
import 'package:trustpin_sdk/trustpin_sdk.dart';

await TrustPin.shared.setupWithNativeBundle();
await TrustPinAttest.shared.setupWithNativeBundle();
await TrustPinAttest.shared.bindToHeader('Authorization');
await TrustPinAttest.shared.prefetch();

setup makes no verifier call: it validates the configuration and loads a device key from an earlier launch. A second call throws ALREADY_INITIALIZED. prefetch() never throws.

Named instances pair with pinning instances of the same id: TrustPinAttest.instance('id') with TrustPin.instance('id'), which must be set up first.

Bind tokens to the user's session

• bindToHeader('Authorization') binds each token to the value of that request header.
• setTokenBinding(value) binds to a fixed value, such as a session id.

Each clears the other. Only a SHA-256 of the value leaves the device. A binding change renews the token with the existing device key; it's not a new attestation.

If your policy has Require token binding on, no token exists until a binding is known: the state is failed with BINDING_REQUIRED and no retry time. That's expected before sign-in, and attestation resumes as soon as a binding is set.

Send the header

trustpin_sdk's HTTP integrations add the header automatically to HTTPS requests for the attested hosts:

// package:http
final client = TrustPinHttpClient.create();

// Dio: pass the instance so redirects of attested requests are followed
final dio = Dio();
dio.interceptors.add(TrustPinDioInterceptor(dio: dio));

• Requests are never failed by the SDK: when no token is ready in a short, bounded time, the request goes out without the header, and your API decides.
• A header the request already carries is never replaced.
• A redirect never carries the header to another host: the integrations follow redirects of attested GET and HEAD requests themselves, pinning each hop and asking for its own header.

For other HTTP clients:

final headers = await TrustPin.shared.attestationHeaders(
  uri,
  headers: {'Authorization': 'Bearer $session'},
);

and TrustPin.shared.redirectedRequestHeaders(...) for each redirect hop. For non-HTTP transports (gRPC, WebSockets), await TrustPinAttest.shared.getToken() and send it in the TrustPin-Attestation header.

The interceptors check the server's certificate before each request; the request itself goes out on Dart's own connection. Binding the token to the session keeps a token useless outside it.

Sensitive operations: assertions

For an operation that must come from this device, such as a payment, send an assertion next to the token. It binds the device's attested key to a SHA-256 digest of your choice, typically the request body:

import 'package:crypto/crypto.dart';

final body = utf8.encode(jsonEncode({'amount': '1.00', 'to': 'demo'}));
final headers = {'Authorization': 'Bearer $session'};
headers.addAll(await TrustPinAttest.shared
    .assertionHeaders(Uint8List.fromList(sha256.convert(body).bytes)));
await client.post(url, headers: headers, body: body);

• assertionHeaders returns both headers, TrustPinAttest.headerName with the token and TrustPinAttest.assertionHeaderName (TrustPin-Assertion) with the assertion. Each call produces a new assertion: one per operation.
• Your backend passes both headers and its own digest of what it received to your verifier.
• It throws INVALID_DIGEST when the digest isn't 32 bytes, and the usual codes when no token is available.

Verify the token in your API

Your API verifies the token against your verifier's JWKS: signature (ES256), type trustpin-attest+jwt, issuer, audience and expiry, the project (tp.prj), the binding, and that it isn't a debug token in production. In monitor mode, a fail result is expected: log tp.reasons and allow. See docs.trustpin.cloud.

Simulators, emulators and debug tokens

Simulators and emulators can't produce real evidence. Pass a debug token from the build, never from a file:

const debugToken = String.fromEnvironment('TRUSTPIN_DEBUG_TOKEN');
await TrustPinAttest.shared.setupWithNativeBundle(
  debugToken: debugToken.isEmpty ? null : debugToken,
);

flutter run --dart-define=TRUSTPIN_DEBUG_TOKEN=<token>

• It's used on the iOS simulator and in debuggable Android builds (emulators and devices), never on iOS devices or macOS, and never sent in release builds.
• Your policy (Allow debug tokens) and your verifier must both allow debug tokens. Their tokens carry tp.env debug, which production APIs refuse.

State, errors and logging

TrustPinAttest.shared.stateChanges.listen((state) {
  final label = switch (state) {
    TrustPinAttestUnavailable() => 'No token yet',
    TrustPinAttestAttesting() => 'Attesting…',
    TrustPinAttestReady(:final expiresAt) => 'Token ready until $expiresAt',
    TrustPinAttestFailed(:final error, :final retryAt) =>
      'Failed: ${error.code}, next attempt after ${retryAt ?? 'restart'}',
  };
  print(label);
});

• stateChanges emits the current state first, then every change.
• events reports what the SDK did, for your monitoring: keys generated or replaced, attestations and renewals with their durations, refusals and waits with their end, unsupported devices, an unreachable verifier, and assertions. Events never contain a token, a key or a device identifier. New event types can appear in a minor release: keep a default case.

TrustPinAttest.shared.events.listen((event) {
  if (event case TrustPinAttestAttestationSucceeded(:final duration)) {
    metrics.record('attestation', duration);
  }
});

• After a failure no timer runs: nothing is tried before retryAt, and the next request, getToken() or prefetch() after it starts a new attempt. A null retryAt means no new attempt in this launch, until reset() or a restart, except BINDING_REQUIRED, which resumes once a binding is set.
• Errors are TrustPinAttestException with a stable code:

Code	Meaning
INVALID_CONFIGURATION	A configuration value was rejected, or the file is missing
ALREADY_INITIALIZED	setup was called again
NOT_SET_UP	Called before setup
UNSUPPORTED_DEVICE	App Attest is unsupported on this device (iOS, macOS)
EVIDENCE_UNAVAILABLE	The device can't produce the evidence the policy requires
BINDING_REQUIRED	The policy requires a binding and none is set yet
ATTESTATION_FAILED	The verifier refused; see reasons
VERIFIER_UNAVAILABLE	The verifier couldn't be reached, including when strict pinning refuses its host
VERIFIER_INCOMPATIBLE	The verifier is too old for this SDK; update it
INVALID_DIGEST	assertionHeaders got a digest that isn't 32 bytes

New codes can appear in a minor release: handle unknown ones.

• Logging is off by default: setLogLevel(TrustPinAttestLogLevel.debug) in development, and TrustPinAttest.logs to route messages. Logs never contain tokens, key certificates, bound values or debug tokens.
• reset() discards the device key, so the token's sub changes. It's for support flows, not routine use, and does nothing before setup.

Backups and privacy

• Device keys and key certificates are never backed up or synced: a restored app attests again.
• Evidence and tokens go only to your verifier, nothing to TrustPin.
• iOS and macOS: the Swift package ships a privacy manifest (no tracking, no collected data).
• Android: with a Google Cloud project number configured, the app uses the Play Integrity API; declare it in Play Console's Data safety form.

Example

The sample app has an Attestation tab: setup, a protected call with a token bound to the Authorization header, a sensitive call with an assertion, sign-out and reset, with the SDK's events in the tab's log.