lorawan: add initial LoRaWAN stack support

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

lora/lorawan/session.go

@@ -0,0 +1,90 @@
+package lorawan
+
+import (
+	"crypto/aes"
+	"encoding/binary"
+	"errors"
+	"math"
+)
+
+// Session is used to store session data of a LoRaWAN session
+type Session struct {
+	NwkSKey    [16]uint8
+	AppSKey    [16]uint8
+	DevAddr    [4]uint8
+	FCntDown   uint32
+	FCntUp     uint32
+	CFList     [16]uint8
+	RXDelay    uint8
+	DLSettings uint8
+}
+
+// GenMessage Forge an uplink message
+func (s *Session) GenMessage(dir uint8, payload []uint8) ([]uint8, error) {
+	var buf []uint8
+	buf = append(buf, 0b01000000) // FHDR Unconfirmed up
+	buf = append(buf, s.DevAddr[:]...)
+
+	// FCtl : No ADR, No RFU, No ACK, No FPending, No FOpt
+	buf = append(buf, 0x00)
+
+	// FCnt Up
+	buf = append(buf, uint8(s.FCntUp&0xFF), uint8((s.FCntUp>>8)&0xFF))
+
+	// FPort=1
+	buf = append(buf, 0x01)
+
+	fCnt := uint32(0)
+	if dir == 0 {
+		fCnt = s.FCntUp
+		s.FCntUp++
+	} else {
+		fCnt = s.FCntDown
+	}
+	data, err := s.genFRMPayload(dir, fCnt, payload, false)
+	if err != nil {
+		return nil, err
+	}
+	buf = append(buf, data[:]...)
+
+	mic := calcMessageMIC(buf, s.NwkSKey, dir, s.DevAddr[:], fCnt, uint8(len(buf)))
+	buf = append(buf, mic[:]...)
+
+	return buf, nil
+}
+
+func (s *Session) genFRMPayload(dir uint8, fCnt uint32, payload []byte, isFOpts bool) ([]byte, error) {
+	k := len(payload) / aes.BlockSize
+	if len(payload)%aes.BlockSize != 0 {
+		k++
+	}
+	if k > math.MaxUint8 {
+		return nil, errors.New("Payload too big !")
+	}
+	encrypted := make([]byte, 0, k*16)
+	cipher, err := aes.NewCipher(s.AppSKey[:])
+	if err != nil {
+		panic(err)
+	}
+
+	var a [aes.BlockSize]byte
+	a[0] = 0x01
+	a[5] = dir
+	copy(a[6:10], s.DevAddr[:])
+	binary.LittleEndian.PutUint32(a[10:14], fCnt)
+	var ss [aes.BlockSize]byte
+	var b [aes.BlockSize]byte
+	for i := uint8(0); i < uint8(k); i++ {
+		copy(b[:], payload[i*aes.BlockSize:])
+		if !isFOpts {
+			a[15] = i + 1
+		}
+		cipher.Encrypt(ss[:], a[:])
+		for j := 0; j < aes.BlockSize; j++ {
+			b[j] = b[j] ^ ss[j]
+		}
+		encrypted = append(encrypted, b[:]...)
+	}
+	return encrypted[:len(payload)], nil
+}
+