  Subscription privacy of a user has been a historical concern with all the
previous generation mobile networks, namely, GSM, UMTS,and LTE. While a little
improvement have been achieved in securing the privacy of the long-term
identity of a subscriber, the so called IMSI catchers are still in existence
even in the LTE and advanced LTE networks. Proposals have been published to
tackle this problem in 5G based on pseudonyms, and different public-key
technologies. This paper looks into the problem of concealing long-term
identity of a subscriber and presents a technique based on identity based
encryption (IBE) to tackle it. The proposed solution can be extended to a
mutual authentication and key agreement protocol between a serving network (SN)
and a user equipment (UE). This mutual authentication and key agreement
protocol does not need to connect with the home network (HN) on every run. A
qualitative comparison of the advantages and disadvantages of different
techniques show that our solution is competitive for securing the long-term
identity privacy of a user in the 5G network.
