Patent ID: 8374338

Claim:
A method for testing a transport packet decrypting module of a client device, said method comprising steps performed by a processing apparatus of: implementing a first decryption operation of the transport packet decrypting module on a test encrypted control word using a content decryption key ladder to derive a test control word; implementing a second decryption operation of the transport packet decrypting module on a test transport packet using the test control word via a predetermined content decryption algorithm, wherein implementing the second decryption operation further comprises: implementing the second decryption operation of the transport packet decrypting module on a test transport packet to decrypt the test transport packet, wherein the test transport packet contains a payload of at least one full encryption block, using the test control word via a first predetermined content decryption algorithm to derive a first KIV; implementing the second decryption operation of the transport packet decrypting module on the test transport packet to decrypt the test transport packet, wherein the test transport packet contains a payload of less than one full encryption block, using the test control word via a second predetermined content decryption algorithm to derive a second KIV; deriving a key integrity value (KIV) from the decrypted test transport packet; and comparing the derived KIV with a value stored in the client device to verify whether the transport packet decrypting module of the client device is functioning properly.