UnconfirmedDataDown decoding

k3pto · April 29, 2025, 4:18pm

I am successfully send a HEX message, using the Enqueue feature, to my end node: Dragino LHT65S. When I look at the UnconfirmedDataDown message in LoRaWAN frames where can I see the data I sent? I have tried using Base64 decoders on Phy_payload:frm_payload with no success.

Liam_Philipp · April 29, 2025, 4:24pm

This may help:

k3pto · April 29, 2025, 5:53pm

Hello Liam,
Thank you for the links. There is quite a bit of data there but I could not find anything helpful. Maybe I am suffering from information overload.

Liam_Philipp · April 30, 2025, 4:41pm

The short answer is there is no easy way. The payload is encrypted and you must use your session key to decrypt it (networkSkey if its a MAC command, appSKey otherwise). The link above provided some repositories for doing so. Although I should preface this that I have never actually used these myself, but I think you are specifically looking for the function:

github.com/brocaar/lorawan

phypayload.go

a18a1037da07


      
          		return err
          	}
          
          	// store the encrypted data in a DataPayload
          	macPL.FRMPayload = []Payload{&DataPayload{Bytes: data}}
          
          	return nil
          }
          
          // DecryptFRMPayload decrypts the FRMPayload with the given key.
          func (p *PHYPayload) DecryptFRMPayload(key AES128Key) error {
          	if err := p.EncryptFRMPayload(key); err != nil {
          		return err
          	}
          
          	macPL, ok := p.MACPayload.(*MACPayload)
          	if !ok {
          		return errors.New("lorawan: MACPayload must be of type *MACPayload")
          	}
          
          	// the FRMPayload contains MAC commands, which we need to unmarshal

While this function is for uplinks, I don’t see why it wouldn’t work for downlinks as well.