How to correctly create a LoraWan packet

Matthis_Foulonneau · January 12, 2020, 5:58pm

Hi Guys !
I am currently working on a project and I am using the Radiohead library for my end nodes because it provides routing functions so a node can relay a message to the Gateway.
because the Radiohead Library does not create LoraWan packets I would like to know if it is possible to create the packet directly on the gateway ?
I know it is less secure and not LoraWan compliant.
Did anyone know how to build a Lorawan packet like this one in C ?
MacHeader[1] | DevAddr[4] | FCtrl[1] | FCnt[2] | FPort[1] | Payload | MIC[4]
Especially how to generate the MIC.
To keep it simple I would like to use APB for authentification with the Network Server.

eugenev · January 12, 2020, 6:29pm

refer to developer docs, regarding your endnode controller. in many cases all the controllers has a software development tools with examples.

No. gateways only translate the LoRaWAN radio frames to IP.

cjhdev · January 13, 2020, 1:58am

You might be able to lift most of the code from one of the many device implementations that are written in C. The tricky part will be working out why the MIC is being rejected if you have made a mistake somewhere.

The spec doesn’t come with any worked examples to verify against. I have a few test inputs you might find useful here.

Matthis_Foulonneau · January 14, 2020, 2:51pm

Thank you guys !
I found what I was looking for to compute MIC here:

github.com

things4u/ESP-1ch-Gateway-v6.0/blob/master/ESP-sc-gway/_sensor.ino#L302


// Parameters:
//	- data:			uint8_t array of bytes = ( MHDR | FHDR | FPort | FRMPayload )
//	- len:			8=bit length of data, normally less than 64 bytes
//	- FrameCount:	16-bit framecounter
//	- dir:			0=up, 1=down
//
// B0 = ( 0x49 | 4 x 0x00 | Dir | 4 x DevAddr | 4 x FCnt |  0x00 | len )
// MIC is cmac [0:3] of ( aes128_cmac(NwkSKey, B0 | Data )
//
// ----------------------------------------------------------------------------
uint8_t micPacket(uint8_t *data, uint8_t len, uint16_t FrameCount, uint8_t * NwkSKey, uint8_t dir) {




	//uint8_t NwkSKey[16] = _NWKSKEY;
	uint8_t Block_B[16];
	uint8_t X[16];
	uint8_t Y[16];
	
	// ------------------------------------
	// build the B block used by the MIC process
	Block_B[0]= 0x49;						// 1 byte MIC code