Lora packet Decoding

[codecandy2015]

Hi Anthony, I find your work on LoRa packet decoding quite intersting. I am currently exploring LoRAWAN with TTN. I have hard time decoding these payloads.

My data is: 7B226D656173757265496473223A5B315D2C2276616C756573223A5B32325D2C2270726F66696C654964223A313030327D

to me this looks like a HEX string.

I am following the same example you have provided in this GitHUB. How ever when I use the nwSKey and AppSKey, I am not able to see my payload decoded.

The MIC check fails. Is there a way to cross check the decoding process ? any help is appreciated Dom

[anthonykirby]

You're correct that this looks like hex - did you try a hex decoder? :-)

The lora-packet library is aimed at users who have the raw "wire-level" data, like you'd see going through a gateway. Your example is the decoded data from TTN, so all the LoRa decoding has happened already.

[codecandy2015]

Hi Anthony,Thanks for your reply. I took this payload on the data console of the TTN. It was hex. I was able to use your web interface and got the payload which was base64 encoded. I was able to see the original message. I am trying something similar on the loriot network. I get the following payloads..

NwSKey = 12C822012DCC304E7CD161CA7F98D29C AppSKey = 80B654DBB82CC7C1D4F9E5139F327F71

JSON up: {"rxpk":[{"tmst":354089252,"chan":6,"rfch":1,"freq":903.500000,"stat":1,"modu":"LORA","datr":"SF10BW125","codr":"4/5","lsnr":14.0,"rssi":-29,"size":29,"data":"QKGfmAGAkQAClKBkJAt8EcGHPldTfy+u8mM8cDk="}]}INFO: [down] PULL_ACK received in 332 ms INFO: Received pkt from mote: 01989FA1 (fcnt=144) JSON up: {"rxpk":[{"tmst":339084708,"chan":1,"rfch":0,"freq":902.500000,"stat":1,"modu":"LORA","datr":"SF10BW125","codr":"4/5","lsnr":13.8,"rssi":-31,"size":29,"data":"QKGfmAGAkAACRZ7Vgm33Uj8TwpSOOya1hhJ/ojw="}]}INFO: [down] PULL_ACK received in 551 ms INFO: Received pkt from mote: 01989FA1 (fcnt=145) when I use the same web interface of yours for the data.. I am not able to get the right payload.Am I doing the right thing for this perhaps ? or I need to decode the data in a different way ?any advice would be appreciated. regardsDomnic

Anthony Kirby <notifications@github.com> schrieb am 12:42 Freitag, 9.Juni 2017:

Closed #7.— You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or mute the thread.

[anthonykirby]

Hi Dom, I'm slightly puzzled by your words "your web interface": I only wrote an npm library.

Looking at your data, the "QKGfmAGAkQAClKBkJAt8EcGHPldTfy+u8mM8cDk=" is Base64, and is probably a raw packet suitable for decoding using this library. The first byte of your data (in hex) is 0x40, which is a valid LoRa "Message Type" byte meaning "Unconfirmed Data Up".

If you haven't tried this already, I suggest copying my "demo1.js" and substituting your data (converted appropriately). If you get a MIC failure & badly decrypted data, you could retry with the endian-ness of your keys reversed - I've written a bit about endianness in the README.

thanks Anthony

[codecandy2015]

Hi Anthony,Yes I had a look at the demo code and I did try it out. This is the output I get.

C:\dev\nodejs\Workspace\PoCs\ken-lora-decoder>npm start
> ken-lora-decoder@0.0.1 start C:\dev\nodejs\Workspace\PoCs\ken-lora-decoder> node app.js
packet.toString()=Message 
Type = Data  
PHYPayload = 40A19F98018091000294A064240B7C11C1873E57537F2FAEF2633C7039
( PHYPayload = MHDR[1] | MACPayload[..] | MIC[4] )        
MHDR = 40  
MACPayload = A19F98018091000294A064240B7C11C1873E57537F2FAEF2         
MIC = 633C7039
( MACPayload = FHDR | FPort | FRMPayload )        

FHDR = A19F9801809100      
 FPort = 02 
 FRMPayload = 94A064240B7C11C1873E57537F2FAEF2
      ( FHDR = DevAddr[4] | FCtrl[1] | FCnt[2] | FOpts[0..15] )     

DevAddr = 01989FA1 (Big Endian)      
FCtrl = 80        
FCnt = 0091 (Big Endian)      
FOpts = Message Type = Unconfirmed Data Up   
Direction = up       
FCnt = 145   
FCtrl.ACK = false   
FCtrl.ADR = true
packet 
MIC=633c7039
FRMPayload=94a064240b7c11c1873e57537f2faef2
MIC check=OK
calculated MIC=633c7039
Decrypted='       �.ʋ��@�p'
============ Finishing Decoding LoRA packet

There you see MIC is OK. but that there is something fishy with the the Decrypted text ? CheersDom

[anthonykirby]

Hi Dom, is it possible that your data is binary? In that case, you'd expect garbage from "toString" Ant

[codecandy2015]

Hi Anthony, I tried to do lora_packet.decrypt(packet, AppSKey, NwkSKey).toString('hex')

I do get a HEX string like this 00000000000000fe2eca8bacaa40a670

But I tried to convert this to base64 also to Ascii but none of these convertions get me anywhere. I am not sure if it was sent as Binary.. as I just get the payload as a JSON file. if it is a Binary data.. how coud I get it back as ASCII text ? do you have any recommendations perhaps ? regards Dom

[anthonykirby]

Hi Dom, that's great, so the decryption worked! (Failed decryption will look like random, not containing strings of zeros).

However, you'll need to investigate the binary format of your data yourself: I can't do this for you.

Anthony

[avbentem]

@anthonykirby

I'm slightly puzzled by your words "your web interface": I only wrote an npm library.

As an aside, that might be my https://runkit.com/avbentem/lorawan-packet-decoder which has a frontend available at https://runkit.io/avbentem/lorawan-packet-decoder/branches/master