if either the transmitter or receiver appears on the revocation list. Updates to the revocation list arrive with new media and are automatically integrated into a device's revocation list. This means that damage can be limited if a key set is exposed or copied. This revocation process does not affect other devices, even if the devices are of the same make and model. KSV values are similar to serial numbers in this sense. As an example of how this system works, if two customers were to buy the same model of television on the same day at the same store, and the first customer hacked their television, the first customer's key could be revoked without affecting the ability of the other customer's television to play content. Attacks on Restricted Authentication If an attacker can find 40 linearly independent vectors () keys ... ()keys (i.e. the vectors generated by adding together a device's Device Key Set based on a KSV,) then they can completely break the HDCP system for all devices using a given Device Key Set. At this point, they can extract the secret key array for any number of KSVs, which allows them to access the shared secrets used in the HDCP authentication protocol. Since the keys generated from the KSVs are produced linearly in the given system (i.e. getting a key from a KSV can be viewed as matrix multiplication), someone could determine the Device Key Set matrix from any 40-50 different systems: .... , and the associated KSV (this is public information from the protocol). In other cases where the extracted keys are not linearly independent, it is still possible to create a new XKey for a new Xksv that is within the span of the ()KSVs (by taking linear combinations) for which the private keys have been found. There will be, however, no guarantee of them satisfying the required property that a KSV must have; 20 ones and 20 zeros. Setting up the Equations Assuming there are 40 () KSVs that are linearly independent (and naming Xkeys the matrix of the keys in the Device Key Set), this gives a set of n linear equations on 40 unknowns – [Xkeys] * (A1)ksv = = [(A1)keys] * Xksv[Xkeys] * (A2)ksv = = [(A2)keys] * Xksv...[Xkeys] * (A40)ksv = = [(A40)keys] * Xksv By having acknowledgment on all the KSVs, and assuming the secret key vectors ()keys are