lorawan: add initial LoRaWAN stack support

Signed-off-by: deadprogram <ron@hybridgroup.com>

lora/lorawan/otaa.go

@@ -0,0 +1,102 @@
+package lorawan
+
+import (
+	"bytes"
+	"crypto/aes"
+	"errors"
+)
+
+// Otaa is used to store Over The Air Activation data of a LoRaWAN session
+type Otaa struct {
+	DevEUI   [8]uint8
+	AppEUI   [8]uint8
+	AppKey   [16]uint8
+	DevNonce [2]uint8
+	AppNonce [3]uint8
+	NetID    [3]uint8
+}
+
+// Set configures the Otaa AppEUI, DevEUI, AppKey for the device
+func (o *Otaa) Set(appEUI [8]uint8, devEUI [8]uint8, appKey [16]uint8) {
+	o.AppEUI = appEUI
+	o.DevEUI = devEUI
+	o.AppKey = appKey
+}
+
+// GenerateJoinRequest Generates a LoraWAN Join request
+func (o *Otaa) GenerateJoinRequest(buf []uint8) error {
+	// TODO: Add checks
+	buf = append(buf, 0x00)
+	buf = append(buf, revertByteArray(o.AppEUI[:])...)
+	buf = append(buf, revertByteArray(o.DevEUI[:])...)
+	buf = append(buf, revertByteArray(o.DevNonce[:])...)
+	mic := genPayloadMIC(buf, o.AppKey)
+	buf = append(buf, mic[:]...)
+	return nil
+}
+
+// DecodeJoinAccept Decodes a Lora Join Accept packet
+func (o *Otaa) DecodeJoinAccept(phyPload []uint8, s *Session) error {
+	if len(phyPload) < 12 {
+		return errors.New("Bad packet")
+	}
+	data := phyPload[1:] // Remove trailing 0x20
+
+	// Prepare AES Cipher
+	block, err := aes.NewCipher(o.AppKey[:])
+	if err != nil {
+		return errors.New("Lora Cipher error 1")
+	}
+	buf := make([]byte, len(data))
+	for k := 0; k < len(data)/aes.BlockSize; k++ {
+		block.Encrypt(buf[k*aes.BlockSize:], data[k*aes.BlockSize:])
+	}
+
+	copy(o.AppNonce[:], buf[0:3])
+	copy(o.NetID[:], buf[3:6])
+	copy(s.DevAddr[:], buf[6:10])
+	s.DLSettings = buf[10]
+	s.RXDelay = buf[11]
+
+	if len(buf) > 16 {
+		copy(s.CFList[:], buf[12:28])
+	}
+	rxMic := buf[len(buf)-4:]
+
+	dataMic := []byte{}
+	dataMic = append(dataMic, phyPload[0])
+	dataMic = append(dataMic, o.AppNonce[:]...)
+	dataMic = append(dataMic, o.NetID[:]...)
+	dataMic = append(dataMic, s.DevAddr[:]...)
+	dataMic = append(dataMic, s.DLSettings)
+	dataMic = append(dataMic, s.RXDelay)
+	dataMic = append(dataMic, s.CFList[:]...)
+	computedMic := genPayloadMIC(dataMic[:], o.AppKey)
+	if !bytes.Equal(computedMic[:], rxMic[:]) {
+		return errors.New("invalid Mic")
+	}
+	// Generate NwkSKey
+	// NwkSKey = aes128_encrypt(AppKey, 0x01|AppNonce|NetID|DevNonce|pad16)
+	sKey := []byte{}
+	sKey = append(sKey, 0x01)
+	sKey = append(sKey, o.AppNonce[:]...)
+	sKey = append(sKey, o.NetID[:]...)
+	sKey = append(sKey, o.DevNonce[:]...)
+	for i := 0; i < 7; i++ {
+		sKey = append(sKey, 0x00) // PAD to 16
+	}
+	block.Encrypt(buf, sKey)
+	copy(s.NwkSKey[:], buf[0:16])
+
+	// Generate AppSKey
+	// AppSKey = aes128_encrypt(AppKey, 0x02|AppNonce|NetID|DevNonce|pad16)
+	sKey[0] = 0x02
+	block.Encrypt(buf, sKey)
+	copy(s.AppSKey[:], buf[0:16])
+
+	// Reset counters
+	s.FCntDown = 0
+	s.FCntUp = 0
+
+	return nil
+}