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.

sedate · May 23, 2025, 7:06am

I think this is where the codec comes in handy. You can find an awesome codec pack that you can bolt onto chirpstack with minimal googleing. Mind you, the dragino codec only covers the uplink events, you would have to add onto it to translate the downlink commands as well.

Liam_Philipp · May 23, 2025, 2:36pm

He’s looking to decode downlinks not uplink

clavisound · May 28, 2025, 6:33am

Same applies for uplinks on the node side. I think you are right.

@k3pto why you want to see the data on the LNS level? You can “see” them in the node.