For DES keys, a unique control vector exists for each type of key the master key enciphers. The cryptographic feature exclusive ORs the master key with the control vector associated with the type of key the master key will encipher. The control vector ensures that an operational key is only 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 Encrypted PIN translate and Encrypted PIN verify functions.