Description in the LTE specification:
When the MME and the UE create an EPS security context using null integrity and null ciphering algorithm during an attach procedure for emergency bearer services, or a tracking area updating procedure for a UE that has a PDN connection for emergency bearer services (see subclause 5.4.3.2), the MME and the UE shall delete the previous current EPS security context.
Input of TPG:
initiate state: UE has not established NAS security context (added by expert)
condition event: the MME and the UE create an EPS security context using null integrity and null ciphering algorithm during an attach procedure for emergency bearer services
expected operation: the MME and the UE shall consider the previous current EPS security context valid.
(negative testing)
Reasoned chain and sentences used:
Reason for condition event
EDG: create an EPS security context == EPS security context taken into use
by ML model
>> This means that we can trigger the event *EPS security context taken into use* to indirectly trigger the event *create an EPS security context*
EDG: MME initiates a security mode control procedure --> EPS security context is taken into use
sentence: The EPS security context is taken into use by the UE and the MME, when the MME initiates a security mode control procedure or ...
>> This means that we can trigger the event *initiates a security mode control procedure* to indirectly trigger the event *EPS security context taken into use*
EDG: send a SECURITY MODE COMMAND message --> initiates the NAS security security mode control procedure
sentence: The MME initiates the NAS security mode control procedure by sending a SECURITY MODE COMMAND message to the UE and ...
>> This means that we can trigger the event *send a SECURITY MODE COMMAND message* to indirectly trigger the event *initiates a security mode control procedure". The parameters can be derived from all the sentence including the description of security requirement and the condition event: the MME and the UE create an EPS security context using null integrity and null ciphering algorithm during an attach procedure for emergency bearer services
Reason for expected operation
>> The expected operation is the same as the one in S2. Please see the *Reason for expected operation* in S2 (click).
Note: the colored phrase are the messages to transmit and the parameters required to set.