## 5 Conclusions  
Fifth-Generation technology has enabled numerous new applications and advanced end user experiences. It also advanced use cases for consumers due to its new approaches in connectivity, scalability, and operability. Finally, 5G technology also provides the foundation upon which future generations of cellular networks will be built. With new opportunities, however, come new risks. User identity privacy in 5G and future 6G networks must be a core consideration for the operators of networks, standards organizations, and the research community. We have reviewed the most important aspects of user identity within 5G CNs, ranging from anonymous network technology, SBA, PII in 5G technology, and the impacts of newly adopted technology to privacy enhancement proposals and lawful interception, concluding in a roadmap for privacy in 6G networks. It was found that user identity and privacy are complex topics within 5G systems due to the newly adopted software-defined solutions that this technology deploys. Privacy is also a topic that is not always well defined, which creates difficulties in creating models that can be standardized in complex systems. Furthermore, with its political implications and the wide variety of privacy laws around the world, it makes it more difficult for standards to be created that ensure that a user's connections are private. Trust in the system is inherently the most important factor for a user to consider while connecting to any 5G network, as the HN ultimately controls all of the encryption processes and thus the ability to gather data on users if protections are not in place. Truly anonymous communications within 5G applications could have real-world benefits for areas such as the healthcare sector, along with government and military operations. Our final insights and key takeaways for further research in this realm are listed below:  
* There exists a strong need to reduce the prevalence and reliance on personal identifiers such as the SUPI (Subscription Permanent Identifier) within 5G/6G Core operations to help better protect user identity. This has the potential to be achieved by replacing the widespread usage of the SUPI between VNFs with decentralized ephemeral identifiers, thereby maintaining 3 GPP standard operations, billing and fraud prevention capabilities, and customer service expectations. This would add a layer of identity abstraction for the user on the network to better protect the SUPI and other identifiers from eavesdroppers and unauthorized behavioral tracking and metadata collection. * Systems can also be designed to leverage the powerful nature of AI to bring enhanced services, experiences, and threat deterrence for users. User datasets must be de-identified to prevent privacy leaks. Continual training methods such as FL preserve user identity protections, as PII is not transmitted to central servers. Concerns may arise from metadata exposure, which may facilitate linkage attacks. * The creation of a standardized trust architecture between users, providers, and third-party vendors would provide visibility and transparency to 5G/6G operations with regard to the data shared or collected by different network elements. Furthermore, adherence to a strict privacy-by-design rationale for newly developed specifications would help to alleviate issues resulting from untrusted third-party vendors or cloud providers. * The incorporation of HSMs into 5G/6G infrastructure to enhance the physical-layer security of cryptographic secrets and to enable end-to-end encryption is a further recommendation for enhancing the privacy and data protection capabilities of these systems. As efforts in 6G conceptualization and technology development continue, it is vital that user identity protections, such as limiting PII metadata within CNs, and privacy considerations are prioritized throughout these efforts in designing future mobile cellular protocols and architectures. Investigation, P.S., M.H., and H.S. ; writing--original draft preparation, P.S. and M.H.