Content for TS 33.401 Word version: 18.1.0

1… 4 5… 6… 6.2… 7… 7.2.5… 7.2.8 7.2.9… 7.3… 8… 9… 10… 11… 15… A… B… C… C.1.6 C.2… C.2.7 C.2.8 C.3… C.4.7 D… E… E.2… E.3… F… G… H… I… K…

10.1 General 10.2 RAU and TAU procedures 10.3 Handover 10.4 Recommendations on AKA at IRAT-mobility to E-UTRAN 10.5 Attach procedures
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10 Security interworking between E-UTRAN and GERAN p. 70

10.1 General p. 70

An SGSN supporting interworking between E-UTRAN and GERAN is capable of handling UMTS security contexts and supports the key conversion function c3 specified in TS 33.102. Such a SGSN is, according to TS 33.102, required to ensure that the UE is authenticated using UMTS AKA, if the UE supports UMTS AKA. Furthermore, the UE must have a USIM to be able to access EPS, except for unauthenticated emergency calls if allowed by regulations. Hence, UMTS AKA is used when the UE is authenticated to the SGSN supporting interworking between E-UTRAN and GERAN even when attached to GERAN, and UMTS security contexts are available. The security procedures for interworking between E-UTRAN and GERAN are therefore quite similar to those between E-UTRAN and UTRAN.

10.2 RAU and TAU procedures p. 70

10.2.1 RAU procedures in GERAN p. 70

This clause covers both the cases of idle mode mobility from E-UTRAN to GERAN and of Idle Mode Signaling Reduction, as defined in TS 23.401.

As the target SGSN and UE are capable of handling UMTS security contexts clause 9.1.1 applies here with the following changes

the target SGSN shall derive GPRS cipher key Kc from CK' and IK' with the help of the key conversion function c3 defined by TS 33.102 , and the target SGSN and UE shall derive GPRS Kc128 as defined by TS 33.102 from CK' and IK' when the new encryption algorithm selected by the target SGSN requires Kc128; the target SGSN and UE shall assign the eKSI value (associated with the CK' and IK') to the GPRS CKSN associated with the GPRS Kc128 .
the target SGSN shall select the encryption algorithm to use in GERAN.

10.2.2 TAU procedures in E-UTRAN p. 71

This clause covers both the cases of idle mode mobility from GERAN to E-UTRAN and of Idle Mode Signaling Reduction, as defined in TS 23.401.

As the SGSN shares a UMTS security context with the UE clause 9.1.2 applies here without changes.

10.3 Handover p. 71

10.3.1 From E-UTRAN to GERAN p. 71

As the target SGSN and the UE are capable of handling UMTS security contexts clause 9.2.1 applies here with the following changes:

the target SGSN shall derive GPRS cipher key Kc from CK' and IK' with the help of the key conversion function c3 as defined by TS 33.102, and target SGSN and UE shall derive GPRS Kc128 as defined by TS 33.102 from CK' and IK' when the new encryption algorithm selected by the target SGSN requires Kc128. The target SGSN and UE shall assign the eKSI value (associated with the CK' and IK') to the GPRS CKSN associated with the GPRS Kc128 .
the target SGSN shall select the encryption algorithm to use in GERAN after handover.
Whether ciphering is considered active in the target GERAN after handover from E-UTRAN shall be determined according to the principles for handover to GERAN in TS 44.060.

10.3.2 From GERAN to E-UTRAN p. 71

10.3.2.1 Procedures p. 71

As the SGSN shares a UMTS security context with the UE clause 9.2.2 applies here without changes.

10.4 Recommendations on AKA at IRAT-mobility to E-UTRAN p. 71

See recommendation provided by clause 9.3.

10.5 Attach procedures |R9| p. 71

10.5.1 Attach in GERAN p. 71

As the SGSN is capable of handling UMTS security contexts clause 9.1.1 applies here with the following changes

the SGSN and UE shall derive GSM cipher key Kc as defined by TS 33.102 from CK' and IK' , and the SGSN and UE shall derive Kc128 as defined by TS 33.102 from CK' and IK' when the new encryption algorithm selected by the target SGSN requires Kc128;
SGSN shall select the encryption algorithm to use in GERAN.