Cryptographic Key Agreement For Mobile Radio

In addition to using integrity keys to protect IMS signal messages, it may be indicated that when providing ip-based services, additional e-mail messages must be exchanged confidentially between an application server computer and the mobile phone terminal. Now, the keys to encrypting the corresponding messages are available in the required applications both in the 103 mobile phone terminal, in the P-CSCF 113 computer only in application server computers 106, 107, without the P-CSCF 113 computer being able to draw conclusions about the derivative keys CKi 318, 322, 323, 324 in application server computers 106 , 107 and vice versa, without the computers in application server 106, 107 being able to draw conclusions about the hardware stored and used in the P-CSCF 113 computer. In the case of a method of creating and distributing cryptographic keys in a mobile phone system, at least one mobile phone system equipped with a mobile phone terminal, a first computer, preferably a computer from a visited communication network (Home Network), a computer from a home communication network (domestic network) and at least one second computer , preferably as an application server computer, is adopted. At least one mobile telephone terminal is preferably located in the area of the communication network visited and authenticated in relation to the domestic communication network and the communication network visited. In this regard, it should be noted that the communication network visited and the home communication network may be the same. As part of the authentication process, authentication key materials have been created, which are stored and available in the mobile phone terminal and in the home communication network computer. The method consists of creating a first cryptographic key and a second cryptographic key from the mobile phone terminal and home communication network computer using authentication key materials. Thus, the first key and the second key will be stored and available in the mobile phone terminal and in the computer of the home communication network. When there are multiple application server computers, an additional cryptographic key will be created by the mobile phone terminal and home communication network computer for each additional application server computer or using the authentication keys, depending on a form of execution of the invention.

The corresponding additional cryptographic key is transmitted to the computer of the associated application server, preferably from the home communication network computer. This means that the IK 314 integrity key is available in the P-CSCF 113 computer, but not in the 103 mobile phone terminal. The [Lacuna] in the 103 mobile phone terminal created the anonymous key AK 316 with the secret key K 306 and the Imperamnummer RAND 304 in the mobile phone terminal 103 with the fifth and third key creation functions f5 315. The first field of 320 authentication creates an EXCLUSIVE-OR link with the AK 316 anonymity key when creating the content of the first field (SQN-AK), thus indicating the mobile phone terminal 103 with the sequential number SQN 302.