def encrypt(self, key, dir):
"""Encrypt FRMPayload
Args:
key (int): AES encryption key - device NwkSKey or AppSkey
"""
if self.payload.frmpayload == None:
return
plen = len(self.payload.frmpayload)
if plen == 0:
return
k = int(math.ceil(plen / 16.0))
# Create the concatenated block S
S = ''
for i in range(k):
Ai = struct.pack('<BLBLLBB', 1, 0, dir, self.payload.fhdr.devaddr,
self.payload.fhdr.fcnt, 0, i + 1)
S += aesEncrypt(intPackBytes(key, 16), Ai)
# Pad frmpayload to a byte multiple of 16
pad = k * 16 - plen
ppl = self.payload.frmpayload + intPackBytes(0, pad)
# Perform the XOR function over the data: unpack 8 bytes
# to long long ints, XOR and repack
pld = ''
for i in range(k):
s = struct.unpack('Q', S[i * 8:(i + 1) * 8])[0]
p = struct.unpack('Q', ppl[i * 8:(i + 1) * 8])[0]
pld += struct.pack('Q', s ^ p)
# Truncate the result to the original frmpayload length
self.payload.frmpayload = pld[:plen]
def encode(self):
"""Create a binary representation of JoinAcceptMessage object.
Returns:
Packed JoinAccept message.
"""
# Encoding Join-accept:
# MAC Header
# 3 bytes appnonce
# 3 bytes netid
# 4 bytes devaddr
# 1 byte dlsettings
# 1 byte rxdelay
# Optional cflist
# Create the message
header = self.mhdr.encode()
msg = intPackBytes(self.appnonce, 3, endian='little') + \
intPackBytes(self.netid, 3, endian='little') + \
struct.pack('<L', self.devaddr) + \
struct.pack('B', self.dlsettings) + \
struct.pack('B', self.rxdelay)
# CFList is not used in a Join Accept message for US/AU bands
if self.cflist:
pass
# Create the MIC over the entire message
self.mic = aesEncrypt(intPackBytes(self.appkey, 16),
header + msg,
mode='CMAC')[0:4]
msg += self.mic
# Add the header and encrypt the message using AES-128 decrypt
data = header + aesDecrypt(intPackBytes(self.appkey, 16), msg)
return data
def checkMIC(self, appkey):
# MIC is calculated over the binary join request message
# excluding the MIC. Use the first four bytes of encrypted
# data, convert from little endian data to int.
data = self.mhdr.encode() + struct.pack('<QQH', self.appeui,
self.deveui, self.devnonce)
aesdata = aesEncrypt(intPackBytes(appkey, 16), data, mode='CMAC')
mic = struct.unpack('<L', aesdata[:4])[0]
return mic == self.mic
def checkMIC(self, key):
"""Check the message integrity code
Args:
key (int): NwkSkey
Returns:
True on success, False otherwise
"""
# Calculate the MIC for this message using key
msg = self.mhdr.encode() + self.payload.encode()
B0 = struct.pack('<BLBLLBB', int('0x49', 16), 0, 0,
self.payload.fhdr.devaddr, self.payload.fhdr.fcnt, 0,
len(msg))
data = B0 + msg
aesdata = aesEncrypt(intPackBytes(key, 16), data, mode='CMAC')
mic = struct.unpack('<L', aesdata[:4])[0]
# Compare to message MIC
return mic == self.mic
def _createSessionKey(self, pre, app, msg):
"""Create a NwkSKey or AppSKey
Creates the session keys NwkSKey and AppSKey specific for
an end-device to encrypt and verify network communication
and application data.
Args:
pre (int): 0x01 ofr NwkSKey, 0x02 for AppSKey
app (Application): The applicaiton object.
msg (JoinRequestMessage): The MAC Join Request message.
Returns:
int: 128 bit session key
"""
# Session key data: 0x0n | appnonce | netid | devnonce | pad (16)
data = struct.pack('B', pre) + \
intPackBytes(app.appnonce, 3, endian='little') + \
intPackBytes(self.config.netid, 3, endian='little') + \
struct.pack('<H', msg.devnonce) + intPackBytes(0, 7)
aesdata = aesEncrypt(intPackBytes(app.appkey, 16), data)
key = intUnpackBytes(aesdata)
return key
def encode(self):
"""Create a binary representation of MACMessage object.
Returns:
String of packed data.
"""
# Calculate the MIC.
# The MIC is calculated as cmac = aes128_cmac(NwkSKey, B0 | msg)
# MIC = cmac[0:3]
# msg is defined as: MHDR | FHDR | FPort | FRMPayload
# B0 is defined as:
# 1 byte 0x49 | 4 bytes 0x00 | 1 byte dir=0 for uplink, 1 for downlink
# 4 bytes devaddr | 4 bytes fcntup or fcntdown
# 1 byte 0x00 | 1 bytes len
msg = self.mhdr.encode() + self.payload.encode()
B0 = struct.pack('<BLBLLBB', int('0x49', 16), 0, 1, self.devaddr,
self.payload.fhdr.fcnt, 0, len(msg))
data = B0 + msg
# Create the MIC over the entire message
self.mic = aesEncrypt(intPackBytes(self.key, 16), data,
mode='CMAC')[0:4]
msg += self.mic
return msg