When the user is attached to a UTRAN, the R99+ VLR/SGSN derives the UMTS cipher/integrity keys from the GSM cipher key using the following conversion functions:

a)   c4: CK_[UMTS] = Kc || Kc;

b)   c5: IK_[UMTS] = Kc₁ xor Kc₂ || Kc || Kc₁ xor Kc₂;

whereby in c5, Kc_i are both 32 bits long and Kc = Kc₁ || Kc₂.

Kc轉(zhuǎn)化成Ck、Ik的實(shí)現(xiàn)，33102上如上所說。關(guān)鍵是如果知道一個(gè)Kc，怎么具體轉(zhuǎn)化成Ck、Ik怎么實(shí)現(xiàn)？ Kc1和Kc2怎么得到的？Ik又如何得到？