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Describe the functions of the Authentication Server Function (AUSF) in the 5G Core network.

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The Authentication Server Function (AUSF) is a critical component within the 5G Core (5GC) network, responsible for managing and overseeing the authentication and authorization processes for subscribers and network entities. Its primary functions include authentication, key generation, and providing security credentials. Below is a detailed technical explanation of the functions of the AUSF:

  1. Authentication and Identity Management:
    • Subscriber Authentication: The AUSF performs the authentication of subscribers (UE - User Equipment) when they connect to the 5G network. It ensures that the UE is a valid and authorized user by verifying the subscriber's identity using authentication methods like Extensible Authentication Protocol (EAP) or other authentication protocols defined in the 5G standards.
    • UE Identity Handling: AUSF manages the subscriber's identity and ensures that the UE's identity information is securely transmitted and stored. This includes handling subscriber-related information such as International Mobile Subscriber Identity (IMSI), User Equipment Identity (IMEI), and other relevant identifiers.
  2. Key Generation and Distribution:
    • Security Key Generation: AUSF is responsible for generating and distributing security keys used in the encryption and integrity protection of user data and signaling messages. These keys include the Access Key (AK), Authentication Key (AKA), and other cryptographic keys required for securing communications.
    • Key Distribution: Once the keys are generated, the AUSF securely distributes them to the appropriate network entities, such as the Access and Mobility Management Function (AMF) and User Plane Function (UPF), to establish secure communication channels.
  3. Security Credential Handling:
    • Subscriber Profile Management: AUSF maintains subscriber profiles containing authentication and security information. This includes information about supported authentication methods, security algorithms, and keying material.
    • Security Credential Storage: The AUSF securely stores and manages sensitive security credentials, ensuring that they are safeguarded against unauthorized access or tampering.
  4. Integration with Other Network Functions:
    • Interaction with AMF: The AUSF closely interacts with the AMF to facilitate UE authentication and session establishment. It provides the AMF with the necessary security parameters and keys required for secure communication.
    • Interaction with Network Exposure Function (NEF): AUSF may interact with the NEF to access subscriber data and policies needed for authentication and authorization decisions.
  5. Subscription Management and Policy Enforcement:
    • Policy Enforcement: AUSF enforces policies related to subscriber authentication and authorization. It ensures that the established security parameters and policies align with the network's security requirements.
    • Subscription Management: AUSF plays a role in managing subscriber subscriptions, ensuring that subscription data is accurate, up-to-date, and accessible when needed for authentication and authorization processes.