A Key Selection Vector (KSV) is a numerical identifier associated with a Device Key Set which is distributed by a Licensor or its designee to Adopters and is used to support authentication of Licensed Products and Revocation as part of the HDCP copy protection system. The KSV is used to generate confidential keys, specifically used in the Restricted Authentication process of HDCP. Restricted Authentication is an AKE method for devices with limited computing resources. This method is used by copying devices of any kind (such as DV recorders or D-VHS recorders) and devices communicating with them for authenticating protected content. The restricted authentication protocol uses asymmetric key management and common key cryptography, and relies on the use of shared secrets and hash functions to respond to a random challenge. Restricted Authentication Protocol The goal of Restricted Authentication is for a device to prove that it holds a secret shared with other devices. One device authenticates another by issuing a random challenge for which the response is generated by combining the shared secrets and multiple hashes. Formally, a Key Selection Vector is a 40-bit vector containing 20 ones and 20 zeros, and is used to specify the random challenge. The Device Key Set is a collection of 40 56-bit values, and is the set of shared secrets for this protocol During the authentication process, both parties (a transmitter and a receiver) exchange their KSVs. Then each device adds (unsigned addition modulo ) its own device secret keys according to a KSV received from another device. If a particular bit in the KSV is set to 1, then the corresponding secret key is used in the addition and otherwise it is ignored. For each set of keys a special key called a KSV (Key Selection Vector) is created. Each KSV has exactly 20 bits set to 0 and 20 bits set to 1. Keys and KSVs are generated in such a way that during this process both devices get the same 56 bit number as a result. That number is later used in the encryption process. Uniqueness and Revocation of KSVs Since valid keys can become compromised (hacked, for instance through reverse engineering hardware), the HDCP scheme includes a mechanism to revoke keys. The KSV values are unique to each key set and, therefore to each device. The HDCP system can then compare these values to a revocation list, and authentication fails