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You can verify a software license without an internet connection, but you cannot revoke it instantly on a device that is still offline. The practical design is to sign a bounded entitlement on your server, verify it in the app with an embedded public key, and require periodic status refreshes so a refund can take effect when the app reconnects.
What offline license verification can—and cannot—do
A digital signature lets an application confirm that an entitlement came from the issuer and has not been altered, without contacting a licensing server for every launch. AWS documents a pattern in which the issuer signs a JSON license with a private key and the application checks it with the corresponding public key. AWS License Manager documentation says signing permits validation “within the application itself, even in an offline environment.”
That verifies the artifact, not the current state of the customer’s purchase. If a customer receives a refund while the app is disconnected, the app cannot learn about it. The signed license remains usable until its expiry or refresh deadline, unless the app receives updated revocation information through another channel. NIST’s digital identity guidance and OWASP token guidance inform the distinction between validating a credential and checking its current status.
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1. Issue a minimal, time-bounded entitlement
Store a server-side entitlement record associated with the sale. Create a structured license containing only what the app needs, such as a license or account identifier, product and feature grants, issue time, and an expiry or refresh deadline. Sign its canonical representation on the server with an asymmetric key. A signed JSON entitlement is one documented implementation pattern; the specific format is a design choice.
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2. Verify before trusting license claims
Embed the corresponding public verification key in the application; never put the signing private key in client code. Verify the signature before using any claims, enforce the license’s time bounds, and allow only configured algorithms and trusted keys. Reject unsigned licenses and artifacts that point to untrusted keys. OWASP ASVS 5.0, V9.1.1, says self-contained tokens should be validated using their digital signature or MAC before their contents are accepted: OWASP Application Security Verification Standard.
3. Process refunds as entitlement-state changes
When your system receives and verifies a refund signal, mark the entitlement revoked and stop issuing renewals. Make the updated status available to the application at its next refresh. The exact payment event, retry handling, and refund policy depend on your payment provider; a signature design alone does not establish those details.
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4. Refresh status when the app can connect
For installations that can go online, refresh at launch or on a clearly documented schedule. A current server response or a signed revocation list can communicate a refund. If the app cannot connect, it has no way to act on the new state until it reconnects or its bounded license expires.
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5. Rotate signing keys without abandoning valid licenses
Use the active private key for new licenses and retain trusted public keys as needed to verify licenses already issued. If a signing key is compromised, rotate or revoke it and decide how affected licenses will be invalidated or reissued. OWASP’s guidance covers prompt key revocation while retaining public keys where they are needed to validate older signatures: OWASP JSON Web Token Cheat Sheet.
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Choose the offline interval as a product trade-off
A maximum offline interval sets the upper bound on how long a refunded license can remain usable without a refresh, assuming the app enforces expiry correctly. Shorter intervals limit that window but require legitimate users to connect more often. Licensing guidance describes the maximum offline period as the latest point by which revocation reaches an online-activated client: Cryptlex offline activation documentation. No universal interval fits every product; select one based on how often users can reasonably connect and how much stale access your refund policy can tolerate.
| Design | Refund access while disconnected | Connectivity for legitimate use | Air-gapped operation | Operational burden |
|---|---|---|---|---|
| Long-lived or non-expiring signed license | May continue indefinitely until the app receives an update | Rare or none | Yes, potentially indefinitely | Low refresh burden, but stale or refunded access is difficult to end |
| Bounded offline license with periodic refresh | Can continue until expiry or the next successful refresh | Required by the configured deadline | Only until the license expires | Requires expiry handling, refresh behavior, and key management |
| Online status check at launch or on a schedule | Can be denied at the next successful check; an offline app may keep working only under its defined grace or expiry rules | Frequent or scheduled connectivity | No, unless paired with a bounded offline grant | Requires reliable service and clear behavior when checks fail |
The first three columns are competing requirements: unlimited disconnection and immediate refund revocation cannot both be guaranteed without an independent communication channel. Decide what the app should do when a license expires or a refresh fails, and explain that behavior to customers before they rely on offline access.
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