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Offline license keys can be verified without a network connection, but they cannot be revoked instantly while a device stays disconnected. The practical design is to sign each entitlement with a server-held private key, verify it in the app with an embedded public key, and set a finite validity period or maximum offline interval. When a refund is confirmed, revoke the server-side entitlement and stop renewing it; the change reaches the app when it reconnects, or takes effect when its current license expires.
Separate offline verification from revocation
A license artifact can prove that the publisher issued it and that its contents have not been altered. It cannot tell a disconnected app that the publisher later changed its mind. These are separate capabilities: a digital signature supports local verification, while revocation requires the client to receive updated information or for its existing authorization to expire.
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AWS documents one pattern: represent an entitlement as JSON and sign it with the issuer’s private key. The app checks the signature using the matching public key, allowing validation “within the application itself, even in an offline environment.” AWS License Manager documentation
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Choose the offline behavior your product can support
There is no design that guarantees both unlimited air-gapped use and immediate revocation after a refund without some independent channel for communicating the change. The choice is a product trade-off: how long a refunded license may remain usable offline versus how often legitimate users must connect.
| Design | Refund behavior while disconnected | Connectivity and operational trade-off |
|---|---|---|
| Long-lived or non-expiring offline entitlement | It remains usable until the app receives revocation information; with no refresh path, it may remain usable indefinitely. | Supports extended or permanent disconnection, but cannot deliver prompt refund revocation to an air-gapped installation. |
| Bounded-duration offline entitlement | It remains usable until its expiration, unless the app reconnects and receives revocation sooner. | Caps the stale period, but users must refresh before expiry to continue using the app. |
| Online refresh at launch or on a schedule | After a confirmed refund is recorded, the next successful refresh can deliver the revoked state. | Provides fresher status when connectivity is available; reliability depends on clients being able to reach the licensing service. |
A maximum offline interval makes the compromise explicit: it is the longest period a client can go without refreshing entitlement status. Shortening it limits how long a refunded license can remain usable without contact, while increasing the burden on users with unreliable or unavailable connectivity. The appropriate interval depends on the product and its users; no universal duration is established here. Keygen licensing-model documentation
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Design the signed entitlement and client checks
Include only the claims the app needs
Use a structured entitlement with fields such as a license or account identifier, product or feature access, issuance time, and an expiry or refresh deadline. Sign a canonical representation on the server using an asymmetric signing key. The signature lets the client detect tampering; it does not make the claims confidential, so avoid placing secrets in the artifact.
Verify before trusting claims
- Parse the artifact without acting on its claims.
- Verify its signature against a trusted public key and an explicitly allowed signature algorithm.
- Reject unsigned artifacts, untrusted key references, invalid signatures, and entitlements outside their permitted time bounds.
- Only after verification succeeds, use the entitlement’s product, feature, or account claims to authorize functionality.
OWASP ASVS 5.0, requirement V9.1.1, says self-contained tokens should be validated using a digital signature or MAC “to protect against tampering before accepting the token’s contents.” OWASP ASVS 5.0, V9.1.1 An algorithm allowlist and trusted key configuration prevent an artifact from choosing how it will be verified.
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Make a refund change server-side, then deliver it
Associate each sale with a server-side entitlement record. When your system receives and verifies a refund signal, mark the entitlement revoked and prevent the system from issuing or renewing it. For online-capable installations, return current entitlement status or a signed revocation update at the next refresh. Refresh at launch or on a documented schedule so users and support teams can understand when status is checked.
The payment provider’s event names, verification requirements, retries, and refund rules depend on that provider and on the applicable policy. Do not treat an unverified notification as proof of a refund; define and test the server workflow against the provider’s own documentation. The architecture alone does not establish any specific processor’s webhook behavior.
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Protect signing keys and plan for rotation
The app needs the public verification key, not the private signing key. Keep the private key under server-side control and restrict which services and operators can use it. If the signing key is compromised, an attacker may be able to create apparently valid licenses, so the response requires more than changing a client setting: rotate or revoke the compromised key, decide how affected entitlements will be handled, and communicate any required reissue.
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Make expiration and failed refresh understandable
When a license reaches its refresh deadline, the app needs a defined behavior rather than an unexplained lockout. Explain when the entitlement expires, what a user should do to refresh it, and what happens if the service is temporarily unreachable. A grace period can improve resilience, but it also extends the period in which a refunded entitlement may remain usable; if you use one, include it in the maximum offline interval and communicate it clearly.
For a truly disconnected installation, use a bounded-duration offline license if refund revocation must eventually take effect. If it must remain usable indefinitely without communication, be explicit that a refund cannot disable that copy until it reconnects or its license is replaced or expires.
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