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Wireless Transfer of Derived Cipher Key by Mobile Station Disclosure Number: IPCOM000004638D
Original Publication Date: 2001-Mar-08
Included in the Prior Art Database: 2001-Mar-08
Document File: 1 page(s) / 20K

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Hans Christopher Sowa: AUTHOR


Wireless Transfer of Derived Cipher Key by Mobile Station

This text was extracted from a WORD97 document.
This is the abbreviated version, containing approximately 100% of the total text.

Wireless Transfer of Derived Cipher Key by Mobile Station

By Hans Christopher Sowa

System Background:

The system is site (cell) based communication system that complies with the TETRA standard. The system uses authentication to restrict access of Mobile Stations (MS) to the system and under normal operation uses one Derived Cipher Keys (DCK) per mobile for confidentiality of communications. The DCK are created during authentication in both the infrastructure and the MS. The DCK are transferred within the infrastructure so that the sites can use them.

The Problem:

The MS roams to a new site that is isolated (local) from the rest of the system. The new site will not be able to obtain the MS' DCK, so the entire site must downgrade its security level from Class 3 to the Class 2. All MS will use the same Static Cipher Key (SCK) in Class 2, which reduces the security significantly from Class 3 where every MS has its own DCK. If the site can obtain the DCK for the MS that roamed in, then the site can remain in Class 3.

The Solution:

The new site will ask the MS to wirelessly transfer the DCK used from the previous site. The MS will request its DCK from the previous site indicating what the new site is so that the previous site can encrypt it with a key that the new site has (but the MS does not have). The MS will take the encrypted DCK obtained from the previous site and will give it to the new site for use on the new site. The new site can trust that the DCK from the MS is authentic since it is encrypted with a key that the MS does not have.