LTE authentication and authorization are essential security functions that verify the identity and access rights of a user equipment (UE) and a network. In 5G, there are two modes of operation: non-standalone (NSA) and standalone (SA). How do these modes affect the LTE security procedures? Let's find out.
In NSA mode, the UE connects to both the LTE and the 5G radio access networks (RANs), but uses the LTE core network (EPC) for control and data services. This means that the LTE authentication and authorization mechanisms are still applied, using the 4G authentication and key agreement (AKA) protocol. The UE and the EPC exchange a series of messages, involving the subscriber identity module (SIM), the home subscriber server (HSS), and the authentication center (AuC), to generate and validate authentication vectors and encryption keys.
In SA mode, the UE connects only to the 5G RAN and uses the 5G core network (5GC) for control and data services. This means that a new authentication and authorization framework is introduced, based on the 5G AKA protocol. The UE and the 5GC exchange a similar series of messages, involving the universal integrated circuit card (UICC), the unified data management (UDM), and the authentication server function (AUSF), to generate and validate authentication vectors and encryption keys. The 5G AKA protocol also supports additional features, such as network slicing, home-routed roaming, and privacy protection.
The LTE and the 5G authentication and authorization procedures have some key differences. The 5G AKA protocol introduces the subscription permanent identifier (SUPI) which can be concealed by a privacy-preserving scheme, called the subscription concealed identifier (SUCI). This prevents the exposure of the user's identity. Additionally, the 5G AKA protocol allows the UE to indicate its preferred network slice, which can affect authentication and authorization process. Furthermore, it enables home-routed roaming so that users can authenticate and authorize with their home network even when connected to a visited network, improving security and efficiency of roaming service, as well as user experience.
The 5G AKA protocol introduces some security enhancements over the LTE AKA protocol, such as stronger cryptographic algorithms and longer key lengths to increase resistance against brute-force attacks or quantum computing threats, a new key hierarchy and derivation scheme to separate keys for different network domains, functions, and slices, and a new security context management scheme to store and update the security parameters and keys for different network connections. These features help avoid key reuse or compromise, unnecessary re-authentication or re-keying.
Despite the security enhancements, the 5G AKA protocol also faces some security challenges. These include interoperability and compatibility issues between the LTE and 5G networks, especially in NSA mode or mixed scenarios. Additionally, scalability and complexity issues of the 5G network architecture can increase the attack surface or overhead of security procedures. Lastly, privacy and trust issues of 5G network users may arise in home-routed roaming or SUCI-based scenarios, where different network operators, regulators, or third parties have access to or influence on the user's identity or data.
The authentication process in each mode: 1. NSA Mode: -In NSA mode, 5G networks are deployed on top of existing LTE infrastructure. The 5G NR is used for data transmission, but LTE is still used for control functions, including authentication. -When a user equipment connects to the network, it initially authenticates with the LTE radio access network using the LTE authentication. -Then LTE RAN, can establish a connection to the 5G NR network for data transmission. 2. SA Mode: -In SA mode, the 5G network operates independently. Both control and data functions are handled by the 5G core network. -Authentication in SA mode involves the 5G protocol, it provides improved security and supports new authentication mechanisms.