Mobile Networks - Authentication Security in 4G & 5G

 ·         Introduction

Mobile Networks are telecommunication networks where we do not have any physical link between the end-user devices and the base transceiver station. The medium between these two is a wireless link through which the end-user gets connected to a mobile network. The device that radiates frequencies is called RF Antenna which can receive the traffic from the end devices.

In the case of mobile networks, the section from a mobile device to the base receiver station is always wireless and the network here onwards is a connected physical network. A sample mobile network architecture has been shown below.

The major concern in mobile networks is the security of the end-user data and the proper recognition of authorized devices to access the network. Therefore, certain authentication procedures are used to authenticate the desired devices.

We will discuss the importance of authentication and procedures in LTE and 5G in the following paragraphs.

 

·         Why do we need authentication in mobile networks?

Mobile networks have made our lives very easy in terms of communication, video, voice, and data sharing. We are connected to each other via our mobile sets and sharing live activities and may be enjoying a cricket match from our favorite location. The time to get tied to Television sets is history now.

But with these facilities, we have encountered privacy and security issues related to privacy and data security. Therefore, the providers are using security technologies to protect our data and privacy.

Authentication is one of the most important aspects that every mobile network must support whether that is a 3G, 4G or, 5G network. Every company prefers the authentication of its users to enable security. In the case of mobile networks, we have a central database where we create a profile for every user in our network. When the user tries to access the network, the device information is forwarded to a dedicated server which matches the profile information with the incoming connection request. When the received information is accurate the node allows the user to access network resources.

So, the core purpose of authentication is to ensure security by either forwarding the user request to access the network or rejecting the unauthorized request for network access. Through the authentication procedure, mobile networks make sure that the traffic transferred over the wireless links is secure and not manipulated by a man in the middle between the device and the base station.

·         Authentication in 4G Networks.

The term LTE is used for “Long term Evolution” which is a form of wireless broadband communication. This technology was designed to provide high-speed data internet only, voice calls are not supported by LTE rather VOIP or VoLTE is used for voice calls over internet protocol. LTE uses a group of transmitting and receiving antennas at both the mobile site and at the base station side. The base station is known as eNodeB in LTE which supports multiple parallel streams to send and receive data.

Below is the LTE architecture and the node that is related to authentication is the home subscriber server (HSS) which is connected to the mobility management entity for receiving and sending subscriber information.

If we study the call flow of LTE, it starts from the UE, which sends attach request towards the enodeB, which directs the attach request towards the MME. Then MME verifies the authenticity of the connection request.  

Below are the authentication procedures that LTE uses for ensuring the security and authentication of incoming connection requests.

LTE Networks are using two security procedures for customer and network information security at two different levels.

·         RRC and User Plane Security between the UE and EUTRAN.

The RRC security association ensures security between the UE and EUTRAN before the subscriber accesses the core network and reaches HSS.

·         NAS Security association between UE and MME.

NAS is the non-access stratum that ensures the security of data transmission between the UE and MME it uses ciphering and protects the integrity of subscriber’s data.

After the association of the device with the core network below are the security procedures parameter that is used for authentication of the subscriber request.

·         RAND: Random Challenge

It is a random value generated by MME and provided to the UE to decode and UE runs an algorithm. The length of the random number is 16 octets.

·         AUTN: Authentication Token

An authentication token is used to provide the authentication information to UE. This is a way to authenticate the network by the UE to check if the network is the one it wanted to get connected.

·         XRES: Expected response

XRES is a parameter that is generated by the MME and sent to HSS and UE, it monitors if both can generate the response that MME expects.

·         EPS-AKA (Evolved Packet System Authentication and Key Management)

This procedure triggers when the UE gets through the initial attach procedure at the EUTRAN end. When it reached the core network MME sends an authentication request message to the HSS. This authentication message consists of UE-related identities like IMSI, PLMN ID, GUTI, etc. The information also contains some authentication vector information which is decoded by HSS and send back to MME and this message is called the Authentication response message.

MME then sends an authentication request to the UE with some authentication vectors and expects a response that MME already generated. When the same response is generated by UE also, this procedure gets completed and both device

·         Authentication in 5G

5G is the latest wireless broadband technology that targets three main things that can’t be provided by current technologies.

ü  eMMB: Enhanced Mobile broadband

ü  URLLC, Ultra reliable low latency less than 1ms.

ü  _mMTC, Massive machine type communication.

5G is the ideal technology that supports IOT and smart cities and large industrial requirements.

 

UDM or unified data management is the main node associated with the authentication and database of the 5G networks. 

5G is a service-based architecture and uses three main security procedures.

·         5G AKA: Authentication and Key Management

·         EAP-AKA: Extensible Authentication Protocol-AKA

·         EAP-TLS: Extensible Authentication Protocol-Transport layer security.

In 5G both AUSF and UDM support authentication functions where the first two procedures are the mandatory authentication procedures and the third one is an optional function. 5G authentication is completed in two phases.

ü  Phase-1: Selection and Initiation of authentication method.

ü  Phase-2: The authentication procedure starts between UE and Network.

After the Selection of the authentication procedure, a few authentication vectors are exchanged and validated at AUSF and UDM. Below is the block diagram showing authentication. 

Below are the necessary authentication vectors used in 5G networks.

EAP-AKA:

It is an authentication procedure in 5G where a cryptographic key is a share between the network and the UE. In the procedure, both network and the UE authenticates each other to ensure the security of information transfer between the network and device.

Here the unified data manager (UDM) generates an authentication vector (AV). Separation for the application management function aka AMF generates a separation bit 1, IK & CK. Then these AV are sent to the AUSF with the instructions to use these authentication vectors for EAP-AKA. The UDF alters these AV (RAND, AUTN, XRES, CK, IK) before it sends them to AUSF.

Conclusion

4G	5G
In 4G authentication HSS & MME plays main role	Entities in 5G are different from 4G particularly SIDF which does not exist in 4G
UE identity over the radio access network is sent unencrypted	The UE permanent ID is always encrypted in 5G
4G authentication is less secure than 5g	5G offers better security with more separation keys

 

Abbreviation

RF                                                          Radio Frequency

LTE                                                              Long term Evolution

VOIP                                                      Voice over IP

VoLTE                                                    Voice over LTE

HSS                                                             Home subscriber Server

UE                                                          User equipment

ENodeB                                                 4G base station

MME                                                      Mobility Management Entity

SGW                                                       serving Gateway.

PCRF                                                       Packet and Charging rule function.

Pgw                                                         Packet Gateway

SAE                                                          Service Architecture Evolution

RRC                                                         Radio resource Control

EUTRAN                                                 Evolved Universal terrestrial Radia access network.

NAS                                                         Network access stratum

IMSI                                                        International mobile subscriber’s identity

gNB                                                         5G Base station

AMF                                                        Application management function

SEAF                                                        Security Anchor Function

AUSF                                                       Authentication server function

UDM                                                       Unified data management

GUTI                                                       Globally unique temporary identity.

CK                                                           Cipher key

IK                                                            integrity Key