SIDF (Subscription Identifier De-concealing function) is a service offered by UDM to resolve SUPI from the SUCI. SUCI stands for subscription concealed identifier and SUPI stands for Subscription Permanent Identifier. When UE registers to the network, it does not send its SUPI rather it uses SUCI to send to network to secure its permanent identity.
In the "Registration Request" NAS message, UE includes its "Mobile identity" as one of the IEs along with other IEs. As per the detail captured in this specification, following possible options would be available with UE to send its identity to network:
- SUCI
- 5G-GUTI
- IMEI
- 5G-TMSI
These are four available identifiers to be sent to network. When network receives SUCI in the registration request, it gets SUPI from this received SUCI by using the SIDF of UDM.
