Patent ID: 7949877

Claim:
A method comprising: obtaining clear form rights information at a client device, said clear form rights information being associated with content stored at said client device; generating a validation hash from at least the clear form rights information; obtaining, by said client device, an external key comprising an integrity secret, wherein said integrity secret is vulnerable based at least in part on its being known to at least an external server device; obtaining a clear form external integrity hash of first data comprising: said clear form rights information and said external key, wherein said clear form external integrity hash is vulnerable based at least in part on said vulnerability of said externally-known integrity secret; obtaining an internal integrity hash of second data comprising: said clear form rights information, said clear form external integrity hash, and an externally inaccessible client device key, wherein said externally inaccessible client device key is not accessible outside said client device and said internal integrity hash is not vulnerable based on a relative comparison with said vulnerability of said externally-known integrity secret; encrypting said internal integrity hash using said externally inaccessible client device key; storing the encrypted internal integrity hash on the client device; decrypting the encrypted internal integrity hash to recover the internal integrity hash; and comparing the validation hash to the internal integrity hash to detect tampering with the rights information.