LoRaWAN uses two-layer AES-128 encryption: the NwkSKey provides frame authentication and integrity (between the device and the Network Server), while the AppSKey encrypts the application payload (between the device and the Application Server).

The Network Session Key (NwkSKey) is an AES-128 key used to compute a CMAC over each frame, which provides both authentication of the sender and integrity of the MAC header and payload. The Application Session Key (AppSKey) is a separate AES-128 key used in AES-CTR mode to encrypt the application payload end-to-end between the device and the Application Server. As a result, the Network Server can route and deduplicate frames but cannot decrypt the application payload — only the Application Server, which holds the AppSKey, can do so. This is a deliberate privacy-by-design pattern: the network operator never sees the customer data in clear.

Never store AppSKey on the same server as the rest of the network state — separating the Join Server, Network Server and Application Server key stores is a key requirement of the LoRaWAN 1.1 security model and good practice even on 1.0.x.