Therefore, you should re-register your device in the backend every time you reset it. As a result, The Things Network will block all messages from the device until the FCntUp becomes higher than the previous FCntUp. When you do this, you should realize that these frame counters reset to 0 every time the device restarts (when you flash the firmware or when you unplug it). This security measure has consequences for development devices, which often are statically activated (ABP). If either the device or the network receives a message with a frame counter that is lower than the last one, the message is ignored. Every time the device transmits an uplink message, the FCntUp is incremented and every time the network sends a downlink message, the FCntDown is incremented. When a device is activated, these frame counters ( FCntUp and FCntDown) are both set to 0. These so-called replay attacks can be detected and blocked using frame counters. It is however possible to re-transmit the messages. Nor is it possible to tamper with them without the NwkSKey, because this will make the MIC check fail. It’s not possible to read these messages without the AppSKey, because they’re encrypted. Frame Counters #īecause we’re working with a radio protocol, anyone will be able to capture and store messages. In The Things Network you can have a default AppKey which will be used to activate all devices, or customize the AppKey per device. Dynamically activated devices (OTAA) use the Application Key ( AppKey) to derive the two session keys during the activation procedure. The application key ( AppKey) is only known by the device and by the application. If you statically activate your device (ABP), these keys stay the same until you change them. If you dynamically activate your device (OTAA), these keys are re-generated on every activation. These two session keys ( NwkSKey and AppSKey) are unique per device, per session. This means that nobody except you is able to read the contents of messages you send or receive. The payload is fully encrypted between the Node and the Handler/Application Server component of The Things Network (which you will be able to run on your own server). The Application Session Key ( AppSKey) is used for encryption and decryption of the payload. In the backend of The Things Network this validation is also used to map a non-unique device address ( DevAddr) to a unique DevEUI and AppEUI. This MIC is similar to a checksum, except that it prevents intentional tampering with a message. This key is used to validate the integrity of each message by its Message Integrity Code (MIC check). The Network Session Key ( NwkSKey) is used for interaction between the Node and the Network Server. These session keys will be used for the duration of the session. The NwkSKey is shared with the network, while the AppSKey is kept private. When a device joins the network (this is called a join or activation), an application session key AppSKey and a network session key NwkSKey are generated. The algorithm used for this is AES-128, similar to the algorithm used in the 802.15.4 standard. LoRaWAN 1.0 specifies a number of security keys: NwkSKey, AppSKey and AppKey.
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