Securing Legacy Interfaces of 5G Short Message Service Function (SMSF)

Network Functions (NFs) in the 5th Generation (5G) mobile communication system face many security-related challenges. Usage of legacy interfaces/protocols is one of them. The Short Message Service Function (SMSF) in the 5G core is the key network function supporting the short message service (SMS) delivery over Non-Access Stratum (NAS) to User Equipment (UE). SMS over NAS is an old service, in existence since the 2nd Generation (2G) mobile communication systems. Therefore, the SMSF in 5G core may need to interface with legacy network elements/functions via non-service based (legacy) interfaces. Typically these legacy interfaces are based on Diameter and/or Mobile Application Part (MAP) protocols. It is essential to secure SMSF records and data (SMS) in transit over these legacy interfaces, as they may contain critical information such as UE identifiers, UE contexts and sensitive financial data. In this work, we present our contributions to 3rd Generation Partnership Project (3GPP)’s Release 19 5G standards, which include the security threats security-related requirements for SMSF’s Diameter and MAP-based legacy interfaces as well as mechanisms to protect SMSF from these threats. These contributions were recently included in 3GPP 5G standards and Indian Telecom Security Assurance Requirements.