Webhook: encrypted frm_payload content?

1

This is quite a basic question, but I’m struggeling to understand the content of the payload that I’ve setup in a webhook integration. I have a Dragino temp sensor (LHT65) which is sending data. On the website I can see the payload as hex (MAC payload: CB9D06EB03050106977FFF). That is the value I’m interested in. Looking at the JSON content the “uplink_message” contains the “frm_payload”, but it is a different value (e.g. “y50G6wMFAQaXf/8=”). Is it correct that the frm_payload is the encrypted version of the hex value? If that’s the case, does anyone know to decrypt that value?

2

No, not correct.

As it’s not decrypted, no one will know how to decrypt that value :wink:

But you can decode it, as can I, it says: CB9D06EB03050106977FFF

It’s encoded as Base64, many decoders via Ms Google, you would benefit from reading:

https://www.thethingsnetwork.org/docs/devices/bytes/

3

Thanks for the quick answer. I might have been a bit unclear. The value in the frm_payload is y50G6wMFAQaXf/8= and not CB9D06EB03050106977FFF. I can see the latter in the overview of the live data, but not in JSON

4

No, I think you were a bit quick not to read what I wrote.

The value in the frm_payload y50G6wMFAQaXf/8= IS CB9D06EB03050106977FFF that has been encoded as Base64.

Your device creates a payload as byte array (documentation link above), but is transferred over the internet in Base64 encoding as you can’t put non-ASCII bytes in to JSON.

1 Like
5

Yes I was a bit quick here, but now I got it. I tried the conversion from base64 with an online converter earlier and that didn’t work. I guess that is why I didn’t “see” the base64 part. Using this JS method gave the correct conversion:

function base64ToHex(str) {
  for (var i = 0, bin = atob(str.replace(/[ \r\n]+$/, "")), hex = []; i < bin.length; ++i) {
    var tmp = bin.charCodeAt(i).toString(16);
    if (tmp.length === 1) tmp = "0" + tmp;
    hex[hex.length] = tmp;
  }
  return hex.join(" ");
}

Thanks for your help.

1 Like