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Is there any way to access NAS messages from LTE network on Android platform? I have all needed software for decoding, but can't get actual message.
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Non-access stratum (NAS) is a functional layer in the NR, LTE, UMTS and GSM wireless telecom protocol stacks between the core network and user equipment. This layer is used to manage the establishment of communication sessions and for maintaining continuous communications with the user equipment as it moves.
NAS Security: The purpose of NAS security is to securely deliver NAS signaling messages between a UE and an MME in the control plane using NAS security keys. The NAS security keys are derived from KASME and new keys are generated every time EPS AKA is performed (every time a new KASME is generated).
Simply put, NAS Integrity (in LTE and UMTS) is to calculate the Message Authentication Code (MAC, shown in Red) using various inputs (shown in Blue and Green) and to calculate MAC-I field in PDCP PDU as illustrated below. The NAS Integrity Algorithm used in LTE is called EIA(EPS Integrity Algorithm).
SMS over NAS This means when making or receiving a call, the UE drops from the 5G RAN to using a 4G (LTE) basd RAN, and then uses VoLTE to make the call the same as it would when connected to 4G (LTE) networks, because it is connected to a 4G network.
NAS messages are present in Baseband log (modem). So, you have to capture Modem Logs in order to check NAS message (or any other OTA Message).
Those messages does not reach the AP (android) side. So, those messages are only present in Modem Logs.
Each modem vendor saves modem log in a different format. They also has its own tool to decode those logs. Some modem vendors are Qualcomm (which has QXDM/QCAT tool), Marvell, Spreadtrum, Intel (or Infineon), Broadcomm (which does not exist anymore), Samsung etc.
Moreover, each Brand (Motorola, Samsung, LG, Asus etc) may have a different implementation to save the logs (hidden keystrings which are usually blocked in end-user version or save logs in the sdcard etc).
So, for example: For Nexus 5, you can search how to save UART Logs and since it uses a Qualcomm modem, I think you can open and read the log using QXDM. However, same procedure wont work in a different model/brand.
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