Patent ID: 7111165

Claim:
A method of authorizing a user device of a key and lock system, wherein said user device is a user key or a lock of a master key system, wherein the master key system enables various persons with different access authorizations to access all relevant items with only one key, the method comprising the following steps: creating said user device having an electronic circuitry comprising an electronic code memory and being arranged to carry out software operations, creating a first system device having an electronic circuitry and being used in a first level of said key and lock system, storing a first encryption key in said user device and said first system device, carrying out an authentication process between said user device and said first system device using said first encryption key, and in case said authentication process was successful, carrying out a software operation by said first system device, by which software operation said encryption key stored in said first user device is replaced by a second encryption key, wherein said second encryption key is stored in second system devices and further user devices used in a second level of said key and lock system, thereby making said user device operable with said second system and further user devices, and wherein, also during the authentication process, said electronic encryption keys in the system devices and first and further user devices are unreadable from outside said electronic circuitry and only used by algorithms executed internally in the user device and wherein, when an encryption key used by the algorithms internally in the user device result in the successful authentication, the encryption key is replaced with another key of a different level.