Hello.
We had a server running for a few months and just now realized that we made a mistake in the way we saved data, meaning a lot of our measurements are incorrect. Luckily I saved all raw lorawan frames (non-decrypted, the raw ones received by MQTT) for a case like this - however, I am now stuck trying to figure out how to decrypt the FrmPayload field of all the old messages.
I have seen this post and a few similar ones, where the answer is to look at the EncryptFRMPayload function here: lorawan/phypayload.go at master · brocaar/lorawan · GitHub
I have tried using that function myself (both re-implementing in another language and just directly using that function in GO) but I cannot manage to get the same (correct) output as the one shown on Chirpstack in the device events page. I have tried all possible combinations of big and little-endianness for the netid, key, and payload, to no avail. Here is the test code:
Relevant info:
- DevAddr: 01c104bf
- Raw data (in the Frmpayload key on chirpstack): 39d6b5dbb79addf619ab6293123c02216a478c3437e9521940ead0dbe5bacb2e040da971677d822a
- fcnt: 276
- application key: 05DB39F25195B42DB1F1B6BE3C127F50
The data shown in chirpstack is FQQCwPqrLwQSuGkUAQIreFACOygCAlmpIAJdBhQMeARwOXIC/RcAAA==, which decoded as hex should be 150402c0faab2f0412b8691401022b7850023b28020259a920025d06140c780470397202fd170000.
For completeness, this is the packet decoded by chirpstack (showing in “events” under the device page):
{
"deduplicationId": "f1ca964d-b63e-41f0-b2c0-39d7fa78cbf4",
"time": "2023-05-03T07:27:04.226+00:00",
"deviceInfo": {
"tenantId": "fa972792-dea5-4143-883a-f76b797e4dd8",
"tenantName": "ourname",
"applicationId": "e489d616-5e79-4cd4-b6a0-cc9bea30b2a4",
"applicationName": "fooapp",
"deviceProfileId": "ad081270-988c-4a52-a157-f81aab5dfa21",
"deviceProfileName": "foo",
"deviceName": "bar",
"devEui": "94193a010b0027fd",
"tags": {}
},
"devAddr": "01c104bf",
"adr": true,
"dr": 0,
"fCnt": 276,
"fPort": 2,
"confirmed": false,
"data": "FQQCwPqrLwQSuGkUAQIreFACOygCAlmpIAJdBhQMeARwOXIC/RcAAA==",
"rxInfo": [
{
"gatewayId": "7076ff0056070a51",
"uplinkId": 18198,
"timeSinceGpsEpoch": "1367134042.226s",
"rssi": -116,
"snr": -20.2,
"location": {
"latitude": xxx,
"longitude": xxx,
"altitude": xxx
},
"context": "PE1GdA==",
"metadata": {
"region_common_name": "EU868",
"region_config_id": "eu868"
}
}
],
"txInfo": {
"frequency": 867100000,
"modulation": {
"lora": {
"bandwidth": 125000,
"spreadingFactor": 12,
"codeRate": "CR_4_5"
}
}
}
}
While this is the “raw” lorawan frame shown on chirpstack:
{
"phy_payload": {
"mhdr": {
"m_type": "UnconfirmedDataUp",
"major": "LoRaWANR1"
},
"mic": [83, 146, 168, 188],
"payload": {
"f_port": 2,
"fhdr": {
"devaddr": "01c104bf",
"f_cnt": 276,
"f_ctrl": {
"ack": False,
"adr": True,
"adr_ack_req": False,
"class_b": False,
"f_opts_len": 0,
"f_pending": False
},
"f_opts": []
},
"frm_payload": "39d6b5dbb79addf619ab6293123c02216a478c3437e9521940ead0dbe5bacb2e040da971677d822a"
}
},
"rx_info": [
{
"context": "PE1GdA==",
"gatewayId": "7076ff0056070a51",
"location": {
"altitude": xxx,
"latitude": xxx,
"longitude": xxx
},
"metadata": {
"region_common_name": "EU868",
"region_config_id": "eu868"
},
"rssi": -116,
"snr": -20.200000762939453,
"timeSinceGpsEpoch": "1367134042.226s",
"uplinkId": 18198
}
],
"tx_info": {
"frequency": 867100000,
"modulation": {
"lora": {
"bandwidth": 125000,
"codeRate": "CR_4_5",
"spreadingFactor": 12
}
}
}
}
What am I doing wrong?
