The Research and Implementation of NAS Signaling Decryption for 5G-R

In network construction and operation, signaling monitoring is a crucial means of troubleshooting network issues and maintaining network stability. Given the extensive application of encryption algorithms in the 5th Generation Mobile Communication-Railways (5G-R), NAS signaling and data are processed with encryption, presenting certain challenges for signaling monitoring. Consequently, studying the testing and verification of NAS signaling encryption and decryption process becomes extremely important for signaling monitoring. At present, research on NAS signaling decryption for 5G-R remains unexplored. Therefore, this paper focuses on the encryption and decryption processes of NAS signaling during terminal access, designing a corresponding decryption and integrity verification scheme, and developing a decryption tool to address challenges such as as key acquisition and derivation, key updates during handover, and the association of signaling with terminals in multi-terminal access scenarios. By fully utilizing the laboratory network management system and the signaling capture and decoding capabilities of Wireshark, successful decryption testing and verification of NAS encrypted messages have been achieved. The final experimental results strongly demonstrate the feasibility of this scheme, enabling effective network state monitoring and analysis of the 5G-R communication system.