What is JA4 and JA4+ Fingerprinting?

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JA4 and JA4+ are advanced methods for fingerprinting SSL/TLS clients and servers, building upon the foundations laid by JA3 fingerprinting. These techniques offer enhanced accuracy and resilience in identifying and tracking network connections, addressing some of the limitations of their predecessor. JA4 focuses on client fingerprinting, while JA4+ extends the concept to include server fingerprinting, providing a more comprehensive view of network interactions.

How JA4 and JA4+ Fingerprinting Work

JA4 Fingerprinting

JA4 creates its fingerprint by combining several elements:

• A truncated hash of the ClientHello message
• The client's port number
• The SNI (Server Name Indication) or ESNI (Encrypted Server Name Indication)
• The ALPN (Application-Layer Protocol Negotiation) list
• Information from the ServerHello, including the selected cipher suite and TLS version

The resulting fingerprint is more detailed and less susceptible to simple evasion techniques compared to JA3.

JA4+ Fingerprinting

JA4+ builds upon JA4 by adding server-side information:

• All components of the JA4 fingerprint
• A truncated hash of the ServerHello message
• The server's port number
• The server's selected ALPN

This combined fingerprint provides a unique identifier for both the client and server involved in a TLS connection.

Applications of JA4 and JA4+

• Enhanced Malware Detection: The more detailed fingerprints allow for better identification of malicious clients and servers, even when they attempt to mimic legitimate traffic.
• Improved Network Visibility: Security teams can gain deeper insights into the nature of encrypted traffic without decrypting it, aiding in threat detection and network analysis.
• Tracking of Malicious Infrastructure: JA4+ can help identify and track malicious servers and command-and-control infrastructure more effectively.
• Protocol Compliance Monitoring: The detailed fingerprints can be used to ensure that clients and servers are adhering to expected TLS configurations and best practices.
• Advanced Rate Limiting: Fingerprints are a powerful way of effectively rate limiting distributed attacks like credential stuffing, denial of service, and web scraping.

Weaknesses and Limitations

While JA4 and JA4+ address many of the weaknesses of JA3, they still have some limitations:

• Complexity: The more complex fingerprinting process may require more computational resources and potentially impact performance in high-traffic environments.
• Potential for Overfitting: The increased granularity might lead to overfitting in detection systems, potentially causing false positives for minor variations in legitimate clients.
• Privacy Concerns: The more detailed fingerprints could potentially be used for user tracking, raising privacy concerns if not implemented responsibly.
• Evasion Techniques: While more resilient than JA3, determined adversaries may still find ways to manipulate their TLS handshakes to evade detection, although this would be significantly more challenging.
• Hashing: While hashing a TLS fingerprint makes for a smaller, consistent fingerprint size and a portable sharing format, hashing the TLS fingerprint has several drawbacks.

JA4 and JA4+ are a significant advancement in TLS fingerprinting techniques over JA3 and JA3S. By incorporating more data points and extending fingerprinting to both clients and servers, these methods offer enhanced capabilities for network security and threat detection.