5G NR Security

Article by Abhijeet Kumar

Introduction to 5G Security

The advent of 5G technology heralds a transformative era for digital communications, offering unprecedented speeds and connectivity for a wide array of devices and services. However, integrating new IT technologies and architectures also brings complex cybersecurity challenges. 5G's architecture not only supports enhanced mobile broadband (eMBB) but also massive machine-type communications (mMTC) and ultra-reliable low-latency communications (URLLC), each with unique security needs.

Securing 5G: Navigating New Cybersecurity Terrain

Key Security Challenges in 5G

1. Network Slicing: Each slice of a 5G network could cater to different service levels and requirements, creating isolated networks within a single physical infrastructure. This isolation demands robust security measures to prevent breaches that could jump from one slice to another, compromising multiple network parts simultaneously.
2. Service-Based Architecture (SBA): 5G introduces a more dynamic architecture where network functions are virtualized. This setup enhances flexibility but increases vulnerability to attacks such as spoofing, tampering, and forgery, necessitating stringent authentication and authorization measures.
3. NFV and CUPS: With network functions virtualization and the separation of control and user planes, traditional security perimeters are blurred. Virtualized functions spread across various physical and cloud-based resources must be meticulously secured to prevent unauthorized access and ensure data integrity.
4. IoT and mMTC: The massive scale of IoT devices connected through 5G networks vastly expands the attack surface. Issues like signaling storms, where large numbers of IoT devices simultaneously send data or requests, can disrupt network operations, highlighting the need for scalable security solutions that can dynamically adapt to varying traffic levels.
5. URLLC: This service scenario requires that 5G networks deliver extremely low latency and high reliability, making traditional security checks that add latency unacceptable. Implementing security measures that do not impede performance is critical, especially in applications like remote surgery or autonomous driving.

Strategies for Enhancing 5G Security

• Advanced Encryption: Implementing state-of-the-art encryption technologies can secure data transmission across increasingly complex networks.
• AI and Machine Learning: Leveraging AI can help in detecting and responding to threats in real time, crucial for maintaining the integrity of high-speed 5G networks.
• Zero Trust Architecture: Adopting a zero trust model, where each network request is treated as a potential threat, can significantly reduce the risk of internal and external attacks.
• Regular Audits and Updates: Continuous monitoring and updating of security protocols is essential to defend against evolving cyber threats.
• Collaboration and Compliance: Working closely with regulators, manufacturers, and service providers to establish and follow standardized security practices can help create a safer 5G ecosystem.

Components of the 5G Security Architecture

User Equipment (UE)

• Identity Confidentiality:Utilizes temporary identifiers like SUCI (Subscription Concealed Identifier).Protects user privacy by masking real identities, preventing tracking and eavesdropping.
• Secure Connection:Ensures both signaling and data are encrypted and integrity-protected.Uses advanced encryption algorithms and sequence integrity codes to prevent data tampering and interception.

AMF (Access and Mobility Management Function)

• Key Management:Derives and manages NAS (Non-Access Stratum) and AS (Access Stratum) keys from the anchor key KSEAF.These keys are crucial for securing communication channels within the network.
• Authentication Coordination:Central point for the UE's authentication processes.Interfaces with AUSF to authenticate UE and synchronize authentication states across the network.

AUSF (Authentication Server Function)

• Authentication Vectors:Manages authentication vectors and parameters essential for the challenge-response authentication mechanism in 5G.
• Key Derivation:Responsible for deriving the anchor key KSEAF from the long-term key K.Ensures secure communications and session management across the network.

UDM (Unified Data Management)

• Key Storage and Management:Serves as a secure repository for subscriber keys and authentication data.Enhances security features and capabilities compared to HSS in 4G.
• Subscription Data Management:Manages detailed subscription information including security policies and user identities.Ensures the integrity and confidentiality of user data.

Security Protocols and Authentication Mechanisms

• 5G AKA (Authentication and Key Agreement):A challenge-response mechanism allowing mutual verification of authenticity between the network and the UE.
• EAP-AKA':An extension of the AKA protocol, optimized for various environments, including non-3GPP networks.Provides a flexible framework to accommodate different authentication methods and security policies.

Key Factors in 5G Security Checks

• Mutual Authentication:Both the network and the UE authenticate each other using shared secrets and cryptographic challenges.Significantly reduces the risk of impersonation and fraud.
• Sequence Number Synchronization:Prevents replay attacks by ensuring that messages are fresh and correctly ordered.
• Anonymity:Uses temporary identifiers to protect the UE's identity from being disclosed over the air.Enhances privacy and prevents potential tracking and targeting.

Security Edge with Network Slicing

• Customized Security Levels:Allows each network slice to implement security measures tailored to the service type it supports.Slices serving IoT devices might focus on integrity and authentication, while those for critical communications may employ robust encryption.
• Isolated Breach Impact:Security breaches in one slice do not affect others.Minimizes overall impact and enhances containment strategies, especially crucial in a diverse network environment with varying security postures and risk profiles.

4G & 5G Key Architecture.

Understanding 5G Authentication Methods

1. EAP-AKA' (Enhanced Authentication Protocol - Authentication and Key Agreement Prime)

• Description: This is an EAP authentication method that builds upon the traditional AKA mechanism, tailored to support integration with USIM (Universal Subscriber Identity Module) for enhanced security.
• Authentication NF (Network Function): AUSF (Authentication Server Function).
• Authentication Vector: Consists of a 5-tuple—RAND (Random number), AUTN (Authentication Token), XRES (Expected Response), CK' (Cipher Key Prime), and IK' (Integrity Key Prime).

Practical Example: A mobile operator might deploy EAP-AKA' to secure a Wi-Fi calling service, allowing seamless and secure authentication when users switch between LTE and Wi-Fi networks. This scenario is common in urban settings where indoor cellular coverage might be poor, and Wi-Fi networks provide a better connection. By using EAP-AKA', the network ensures that authentication is robust and adheres to the security standards required for voice and data services transmitted over public or private Wi-Fi.

2. 5G AKA (5th Generation Authentication and Key Agreement)

• Description: An enhanced version of the EPS AKA used in 4G, 5G AKA includes additional procedures to strengthen security, particularly in scenarios involving roaming, to prevent spoofing attacks. Notably, 5G AKA simplifies the authentication vector by excluding the need for multiple vectors or pre-acquisition of vectors.
• Authentication NF: AMF (Access and Mobility Management Function) and AUSF.
• Authentication Vector: Comprises a 4-tuple—RAND, AUTN, XRES* (Enhanced Expected Response), and KAUSF (Key for AUSF).

Practical Example: Consider an international traveler roaming with their 5G-enabled smartphone. When the UE attempts to connect to the roaming partner's network, 5G AKA ensures that the authentication process is securely managed through the home network's AMF and AUSF, preventing the possibility of the roaming partner spoofing the home network. This mechanism is particularly critical in ensuring that roaming agreements and security protocols are adhered to, protecting the user's data from unauthorized access or fraud during international travel.

Choosing the Right Authentication Method

Carriers must select the appropriate authentication method based on a variety of factors:

• Security Requirements: Depending on the level of security needed, carriers might opt for 5G AKA for its enhanced security features, especially in scenarios prone to spoofing and fraud.
• Network Configuration: The choice might also depend on the network’s existing architecture and the ease of integrating these authentication methods with legacy systems.
• Regulatory Compliance: Different regions may have specific regulatory requirements that influence the choice of authentication methods, particularly regarding user privacy and data protection.

Understanding the 4G and 5G Key Architectures

The image you provided illustrates the key architecture differences between 4G and 5G networks. Let’s break down each architecture and understand the specific enhancements that make 5G security superior to 4G.

4G Key Architecture

Key Derivation:

K: The master key stored in the Authentication Center (AuC) and the USIM.

CK, IK: Ciphering Key and Integrity Key derived from K and used for encryption and integrity protection of signaling.

K_ASME: Key derived from CK and IK used by the Mobility Management Entity (MME) to derive NAS (Non-Access Stratum) keys.

Authentication and Key Management:

HSS (Home Subscriber Server): Manages authentication vectors and subscriber information.

MME: Manages NAS signaling security using keys K_NASint and K_NASenc.

eNodeB: Manages radio signaling and user plane security with keys derived from K_ASME.

Security Keys:

KeNB, NH: Keys derived from K_ASME used for radio resource control (RRC) and user plane encryption (UP).

KRRCint, KRRCenc, KUPenc: Derived keys for integrity and encryption of RRC and UP messages.

5G Key Architecture

Key Derivation:

K: The master key stored in the Unified Data Management (UDM) and the USIM.

CK, IK: Ciphering and Integrity Keys, similar to 4G, but with enhanced management.

K_AUSF: Derived by the AUSF for secure authentication.

K_SEAF: Derived by the SEAF (Security Anchor Function) for anchoring security between AMF (Access and Mobility Management Function) and UE.

K_AMF: Specific to the AMF, derived from K_SEAF for NAS signaling protection.

Authentication and Key Management:

UDM: Stores subscriber root keys and handles authentication data.

AUSF: Manages authentication processes and derives K_AUSF.

AMF: Derives K_AMF from K_SEAF and manages NAS signaling security.

Security Keys:

K_N3IWF: Used for untrusted non-3GPP access.

KgNB, NH: Keys used for securing gNodeB communications.

KRRCint, KRRCenc, KUPint, KUPenc: Derived keys for integrity and encryption of RRC and user plane messages, respectively.

Differences from 4G Security and Improvements in 5G Security

Unified Security Framework:

4G: Uses different authentication methods for 3GPP and non-3GPP accesses.

5G: Employs a unified framework that supports both 3GPP and non-3GPP accesses, simplifying security management and reducing potential vulnerabilities.

Enhanced Authentication Protocols:

EAP-AKA': Enhanced Authentication and Key Agreement protocol for non-3GPP access, providing better integration and security.

5G AKA: An improved version of EPS AKA with added home network authentication confirmation to prevent spoofing attacks during roaming.

Advanced Key Management:

Dynamic Key Derivation: 5G dynamically derives keys at multiple levels (e.g., K_SEAF, K_AMF) to isolate different security domains and prevent key reuse.

Session-Specific Keys: Unique keys for each session and service (e.g., KUPint, KUPenc) enhance security granularity and minimize the impact of key compromise.

Improved Privacy Protection:

SUCI: Subscription Concealed Identifier used to protect subscriber identity over the air, preventing tracking and eavesdropping.

How 5G Security Works: Algorithms and Processes

Initial Authentication:

UE Initialization: The UE generates a Subscription Concealed Identifier (SUCI) and sends it to the network.

AMF and AUSF Interaction: The AMF receives the SUCI, retrieves subscriber data from the UDM, and coordinates with the AUSF for authentication.

Key Derivation and Distribution:

K_AUSF Generation: AUSF derives K_AUSF from the master key K.

K_SEAF Derivation: SEAF uses K_AUSF to derive K_SEAF.

K_AMF Derivation: AMF derives K_AMF from K_SEAF, providing a session-specific key for NAS signaling.

Service-Specific Security:

Radio Access Security: gNodeB uses KgNB and NH keys for RRC and user plane encryption and integrity.

Non-3GPP Access: K_N3IWF secures untrusted non-3GPP access points.

Ongoing Security Maintenance:

Key Refresh and Rotation: Regularly updates keys to prevent long-term usage vulnerabilities.

Re-authentication Procedures: Periodically re-authenticates UE to ensure continuous security.