Flutter Licensing

Offline, fail-closed Ed25519 license verification and feature entitlements for Flutter. The backend remains the only issuer; this package contains public keys only and performs no networking or payment processing.

Certificate

The certificate is JSON containing base64url-encoded payload and signature. Verification is performed over the original decoded payload bytes. A payload's signed key_id selects a preconfigured trust key and can never introduce its own key.

{"payload":"<base64url>","signature":"<base64url>"}

Setup

Add public-key assets to the host application's pubspec.yaml:

flutter:
  assets:
    - assets/license_keys/license-2026-01.pub

The filename follows the signed key ID: "key_id": "license-2026-01" resolves to assets/license_keys/license-2026-01.pub.

final keys = LicenseKeyRegistry();
await keys.addAsset('license-2026-01');

final verifier = LicenseVerifier(
  keyRegistry: keys,
  productIdentifierProvider: const PackageInfoProductIdentifierProvider(),
  clock: TrustedClock(storage: const SecureTrustedTimeStorage()),
);

final rules = FeatureEntitlements()
  ..allowWithoutLicense(const LicenseFeature('basic'))
  ..allowForPlans(const LicenseFeature('export'), [3, 67]);

final licensing = FlutterLicensing(
  verifier: verifier,
  storage: const SecureLicenseStorage(),
  entitlements: rules,
	expectedId: customerId,
	expectedDeviceId: deviceId,
	expectedProduct: 'onl.tone.app',
);
await licensing.initialize();
final syncResult = await licensing.sync(
  AtomCyouSyncClient(
    baseUri: Uri.parse('https://atom.cyou'),
    project: 'my-project',
  ),
  customerId,
);
final result = await licensing.importLicense(
  certificateText,
  model: LicenseModel.replace,
);
final allowed = await licensing.isFeatureAllowed(const LicenseFeature('export'));

Keys may instead be supplied as 32 raw bytes, base64/base64url, or an RFC 8410 PEM public key. Never download a key from the same untrusted certificate. Changing a configurable public key changes the application's trust root.

Behavior

  • product must exactly match expectedProduct when supplied, otherwise it must match the running package/bundle identifier.
  • Arbitrary non-negative planId values are valid; optional names never affect validity.
  • Free features work without a license.
  • The signed payload includes the Core/customer identity as id and may include device_id_hash, a SHA-256 digest of a separate high-entropy installation ID.
  • Device-only certificates may omit id. Every certificate and every FlutterLicensing instance must have at least one customer/Core or device identity.
  • SecureDeviceIdentity generates a random 256-bit installation ID and retains it in platform secure storage. Send that value as CorePort deviceid; AtomCyou stores and returns only its signed hash.
  • expectedId verifies the owner. expectedDeviceId is hashed locally before comparison with device_id_hash; it does not replace the owner. Avoid predictable hardware identifiers because an unsalted hash of low-entropy data can be guessed.
  • sync downloads only active AtomCyou certificates and verifies every certificate before updating secure local storage. Network errors preserve offline state; authoritative none and suspended responses remove it.
  • Device-only apps use syncByDevice(client, secureDeviceIdentity), which places only the device hash—not the raw secret—in the AtomCyou URL.
  • Import validates before storage. Same-plan certificates extend only when their expiration is later.
  • LicenseModel.separate (the default) keeps a current license when a different plan is imported.
  • LicenseModel.replace immediately replaces a different plan. A higher plan ID is an upgrade and a lower plan ID is a downgrade; both behave identically during import.
  • Time is UTC and valid in [not_before, expires_at). TrustedClock provides rollback resistance only as a best effort; a permanently offline, attacker-controlled client cannot establish trustworthy wall-clock time.

SecureTrustedTimeStorage persists the clock lower bound using platform secure storage. The included in-memory implementation is intended for tests.

Security

Do not log certificates, signatures, public-key configuration, or Core IDs. Report vulnerabilities privately through GitHub Security Advisories.

License

CORE License. Source-form distributions, modifications, and contributions must remain publicly available.

Libraries

flutter_licensing