CDMA 2000 R-UIM Operations, SSD Controlling

Indeed, There are three prime functions/operations of R-UIM of CDMA 2000 network which are SSD controlling, authentication calculating and encryption keys generating, and call history parameters managing. At this article, let's only talk about SSD Controlling function and let the two others will be talked on the next CDMA 2000 R-UIM operations. CDMA 2000 R-UIM save and control SSD which is used to calculate the authentication response and keys generating.

CDMA 2000 R-UIM's SSD is from A-key which saved at R-UIM. SSD updating is started when the CDMA 2000 network send UPDATE SSD command. UPDATE SSD command is consisted of RANDSSD parameter which is sent to Mobile Equipment (ME). SSD customers updating only can be updated by the customers' home network itself. You can see this updating flow at the picture below:

When the network initiate the SSD update to customers, customers' ME will save the RANDSSD parameter then generate some random numbers which is called as RANDSeed. Then, ME start Base Station Challenge by sending RANDSeed parameter to R-UIM. This step makes that ME generate RANDBS. Get Response command tell R-UIM to send RANDBS to ME and then forward it to network.

At next step (at picture below), ME run the SSD update function by sending a command to R-UIM which consisted of RANDSSD parameter and control data field. Then, R-UIM calculate the new SSD value as well as calculate the expected value from network response of RANDBS which is called as AUTHBS. The ESN and IMSI which are used at this step, is decided when R-UIM plug in into ME.

At the network, RANDSSD parameter is also used to generate new SSD value. When RANDBS is accepeted from ME, CDMA 2000 network combines it with new SSD to calculate AUTHBS. Then, AUTHBS is sent from network to ME. ME forwards AUTHBS value (that accepted before) to R-UIM. This AUTHBS value acts as Confirm SSD parameter. Then, R-UIM compares AUTHBS value that calculated with AUTHBS value that sent by network.

If the value is same, it means the SSD update procedure is success. Then, the new SSD value is saved at R-UIM semi-permanent memory and will be used for the entire authentication calculating. If the AUTHBS value is not same, R-UIM will discard it and still use the old value.