CDMA 2000 R-UIM Operation, Authentication Calculation and Encryption Keys Generating

As I told in previous article about CDMA 2000 R-UIM Operation, there are three prime function of CDMA 2000 R-UIM card which are SSD controlling, authentication calculation, and encryption keys generating. The Authentication calculation has been discussed on the previous CDMA 2000 R-UIM Operation article. Therefore, now, I will discuss about Authentication Calculation and Encryption Keys Generating of CDMA 2000 R-UIM in this article.

Instead discuss the Authentication Calculation and Encryption Keys in separate article, I think it is better discuss both of them in single article. It is because both of them is also said as one function since work together on same time to run the Run CAVE function as below picture:

UIM record the International Mobile Subscriber Identity (IMSI) – both of the IMSI_M and IMSI-T – for users identification. The ten bottom digit is coded into 34 bit subset which called as IMSI_M_S and IMSI_T_S. Then, each of IMSI_M_S and IMSI_T_S is devided into 24 bits be IMSI_M_S1 and IMSI_T_S1 as well as IMSI_M_S2 and IMSI_T_S2. IMSI_M_S1 and IMSI_T_S1 is for bottom 7 bits identification and IMSI_M_S2 and IMSI_T_S2 is for the other 3 bits. For authentication calculation, 24 bits of bottom 7 digits is used in most of applications.

IMSI that used for the authentication calculation is determined when the R-UIM is plugged-in into Mobile Equipment (ME). The Get Response command UIM to convey the AUTHR output or AUTHU (global chalenge response or unique challenge response) to ME. The temporary parameter will be recorded in UIM which used on ciphering keys calculation. This ciphering keys calculation is done by running the Generate key/VPM function. The Generate Key/VPM function is shown on the below piccture:

Generate Key/VPM function will produce keys for ciphering mechanism. Generate Key/VPM function will process the several parameters that produced by authentication response from Run CAVE function. Several keys that produced by Generate Key/VPM will be used directly by ME for encryption function. The others will be further processed inside the ME for EMMEA functions.