For each type of DES key the master key enciphers, there is a unique control vector. The cryptographic feature exclusive ORs the master key with the control vector associated with the type of key the master key will encipher. For example, all the different types of DATA, PIN, MAC, and transport keys are each exclusive ORed with a unique control vector. The control vector ensures that an operational key can only be used in cryptographic functions for which it is intended. For example, the control vector for an input PIN-encrypting key ensures that such a key can be used only in the PIN translation and PIN verification functions. Types of DES keys describes the different DES key types.