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dji_mvfc_fwpak.py
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dji_mvfc_fwpak.py
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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
""" DJI Mavic Flight Controller Firmware Crypto tool.
Handles the second level encryption used for Flight Controller modules
in Mavic and newer drones.
"""
# Copyright (C) 2018 Jan Dumon <jan@crossbar.net>
# Copyright (C) 2018 Freek van Tienen <freek.v.tienen@gmail.com>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
__version__ = "0.5.2"
__author__ = "Jan Dumon, Freek van Tienen @ Original Gangsters"
__license__ = "GPL"
import sys
import re
import os
import hashlib
import binascii
import time
import argparse
from Crypto.Cipher import AES
from ctypes import c_char, c_int, c_ubyte, c_ushort, c_uint, c_ulonglong, c_float
from ctypes import memmove, addressof, sizeof, Array, LittleEndianStructure
from os.path import basename
encrypt_key = bytes([0x96, 0x70, 0x9a, 0xD3, 0x26, 0x67, 0x4A, 0xC3, 0x82, 0xB6, 0x69, 0x27, 0xE6, 0xd8, 0x84, 0x21])
encrypt_iv = bytes([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0])
def eprint(*args, **kwargs):
print(*args, file=sys.stderr, **kwargs)
class EncHeader(LittleEndianStructure):
_pack_ = 1
_fields_ = [
('target', c_ubyte), # 0
('unk0', c_uint), # 1 Always 0x01000001
('version', c_ubyte * 4), # 5
('unk1', c_ubyte), # 9 Always 0x01
('size', c_uint), # 10
('unk2', c_uint), # 14 Always 0x00000000
('time', c_uint), # 18
('unk3', c_ubyte), # 22 Always 0x04
('md5', c_ubyte * 16), # 23
('crc16', c_ushort), # 39 end is 41
]
def __init__(self):
self.unk0 = 0x01000001
self.unk1 = 0x01
self.unk2 = 0x00000000
self.unk3 = 0x04
def dict_export(self):
d = dict()
for (varkey, vartype) in self._fields_:
#if not varkey.startswith('unk'):
d[varkey] = getattr(self, varkey)
return d
def __repr__(self):
d = self.dict_export()
from pprint import pformat
return pformat(d, indent=4, width=1)
def getTarget(self):
tg_kind = self.target & 31
tg_model = (self.target >> 5) & 7
return (str(tg_kind).zfill(2) + str(tg_model).zfill(2))
def getVersion(self):
return ('v' + str(self.version[3]).zfill(2) + '.' + str(self.version[2]).zfill(2) + '.' + str(self.version[1]).zfill(2) + '.' + str(self.version[0]).zfill(2))
def getTime(self):
return (time.strftime('%Y-%m-%d %H:%M:%S', time.localtime(self.time)))
def __str__(self):
s = "Target: {:s}\n".format(self.getTarget())
s += "Version: {:s}\n".format(self.getVersion())
s += "Time: {:s}\n".format(self.getTime())
s += "Size: {:d}\n".format(self.size)
s += "Data MD5: {}\n".format(binascii.hexlify(self.md5))
s += "Header CRC: {:04x}".format(self.crc16)
return s
def calc_checksum(packet, plength):
crc = [0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, 0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e, 0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd, 0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c, 0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb, 0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a, 0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9, 0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738, 0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7, 0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036, 0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5, 0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134, 0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3, 0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232, 0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1, 0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330, 0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78]
v = 0x3692
for i in range(0, plength):
vv = v >> 8
v = vv ^ crc[((packet[i] ^ v) & 0xFF)]
return v
def unpack(args):
header = EncHeader()
if args.input.readinto(header) != sizeof(header):
raise EOFError("Couldn't read image file header.")
print(header)
if (header.crc16 == calc_checksum(bytes(header), 39)):
if (args.verbose > 0):
print("{}: CRC of the header verified.".format(args.input.name))
elif (not args.force_continue):
raise ValueError("CRC of the header doesn't match!")
else:
eprint("Warning: CRC of the header doesn't match!")
blocks_count = (header.size + 255) // 256
data = args.input.read(blocks_count * 256)
# MD5 of the entire file
md5_sum = hashlib.md5()
md5_sum.update(header)
md5_sum.update(data)
md5_calc = md5_sum.digest()
md5_read = args.input.read(16)
if md5_calc == md5_read:
if (args.verbose > 0):
print("{}: File MD5 matches.".format(args.input.name))
elif (not args.force_continue):
raise ValueError("File MD5 doesn't match!")
else:
eprint("Warning: File MD5 doesn't match!")
remaining = args.input.read()
if len(remaining) == 0:
if (args.verbose > 0):
print("{}: Trailing bytes verified.".format(args.input.name))
elif (not args.force_continue):
raise ValueError("Expected no trailing bytes, got {:d}!".format(len(remaining)))
else:
eprint("{}: Warning: Expected no trailing bytes, got {:d}!".format(args.input.name,len(remaining)))
dec_buffer = bytes()
for i in range(blocks_count):
enc_buffer = data[(i * 256):((i + 1) * 256)]
cipher = AES.new(encrypt_key, AES.MODE_CBC, encrypt_iv)
dec_buffer += cipher.decrypt(enc_buffer)
md5_data = hashlib.md5()
md5_data.update(dec_buffer)
md5_calc = md5_data.digest()
if (args.verbose > 0):
print("{}: Decrypted data MD5: {}".format(args.input.name,binascii.hexlify(md5_calc)))
if md5_calc == bytes(header.md5):
if (args.verbose > 0):
print("{}: Decrypted data MD5 matches.".format(args.input.name))
elif (not args.force_continue):
raise ValueError("Decrypted data MD5 does not match!")
else:
eprint("{}: Warning: Decrypted data MD5 does not match!".format(args.input.name))
if args.cmd == 'dec':
args.output.write(dec_buffer[:header.size])
args.output.close()
print("{}: Decrypted file to '{}'".format(args.input.name,args.output.name))
return
def pack(args):
header = EncHeader()
data = args.input.read()
header.size = len(data)
# Target
if args.target == '0305':
header.target = (0x5 << 5) | (0x3)
elif args.target == '0306':
header.target = (0x6 << 5) | (0x3)
else:
raise ValueError("Unknown target: '{}'".format(args.target))
# Timestamp
if args.time is None:
header.time = int(time.time())
else:
if args.time.isdigit():
t = int(args.time, 10)
else:
t = time.strptime(args.time, '%Y-%m-%d %H:%M:%S')
if t is None:
raise ValueError("Wrong format for time: '{}'".format(args.time))
t = int(time.mktime(t))
header.time = t
ver = re.search('^v(\d+).(\d+).(\d+).(\d+)$', args.fwver)
if ver is None:
raise ValueError("Wrong firmware version string format (vAA.BB.CC.DD): '{}'".format(args.fwver))
# Store module version
header.version[3] = int(ver.group(1), 10)
header.version[2] = int(ver.group(2), 10)
header.version[1] = int(ver.group(3), 10)
header.version[0] = int(ver.group(4), 10)
# Prepare for computing MD5 sum of decrypted data
# Obviously padding on last block is included in the decrypted data checksum.
# You decide whether it's made on purpose, or just programmed by an intern.
md5_dec = hashlib.md5()
# Encrypt the file
enc_buffer = bytes()
blocks_size = 256
pad_len = (blocks_size - (len(data) % blocks_size)) % blocks_size
blocks_count = (len(data) + 255) // 256
enc_block = 256 * b'\0'
for i in range(blocks_count):
dec_block = data[(i * 256):((i + 1) * 256)]
if len(dec_block) < 256:
# Last block is padded by data from previous block; this is
# unlikely conscious decision; but that's how it was implemented
dec_block += enc_block[len(dec_block):256]
md5_dec.update(dec_block)
cipher = AES.new(encrypt_key, AES.MODE_CBC, encrypt_iv)
enc_block = cipher.encrypt(dec_block)
enc_buffer += enc_block
# Store MD5 of decrypted data
header.md5 = (c_ubyte * 16)(*(md5_dec.digest()))
# Calculate the header crc
header.crc16 = calc_checksum(bytes(header), 39)
print(header)
args.output.write(header)
args.output.write(enc_buffer)
# Prepare MD5 of the entire file
md5_enc = hashlib.md5()
md5_enc.update(header)
md5_enc.update(enc_buffer)
args.output.write(md5_enc.digest())
args.output.close()
print("{}: Encrypted file to '{}'".format(args.input.name, args.output.name))
def main():
""" Main executable function.
Its task is to parse command line options and call a function which performs requested command.
"""
parser = argparse.ArgumentParser(description=__doc__.split('.')[0])
subparsers = parser.add_subparsers(dest='cmd')
parser.add_argument('-v', '--verbose', action='count', default=0,
help="increases verbosity level; max level is set by -vvv")
parser.add_argument('-f', '--force-continue', action='store_true',
help="force continuing execution despite warning signs of issues")
parser_dec = subparsers.add_parser('dec',
help="decrypt")
parser_dec.add_argument('-i', '--input', required=True, type=argparse.FileType('rb'),
help="name of the input encrypted FC firmware file")
parser_dec.add_argument('-o', '--output', type=argparse.FileType('wb'),
help="name of the output decrypted firmware file")
parser_enc = subparsers.add_parser('enc',
help="encrypt")
parser_enc.add_argument('-i', '--input', required=True, type=argparse.FileType('rb'),
help="name of the input unencrypted FC firmware file")
parser_enc.add_argument('-o', '--output', type=argparse.FileType('wb'),
help="name of the output encrypted firmware file")
parser_enc.add_argument('-T', '--time',
help=("timestamp; if omitted, the current time will be used; the timestamp "
"is either a number (seconds since epoch) or in the following format: "
"\"year-month-day hour:min:sec\""))
parser_enc.add_argument('-V', '--fwver', required=True,
help="firmware version string in the form \"vAA.BB.CC.DD\"")
parser_enc.add_argument('-t', '--target', required=True,
help="either 0305 or 0306")
parser_inf = subparsers.add_parser('info',
help="show header information")
parser_inf.add_argument('-i', '--input', required=True, type=argparse.FileType('rb'),
help="input file")
args = parser.parse_args()
if args.cmd == 'info':
if (args.verbose > 0):
print("{}: Opening for info display".format(args.input.name))
unpack(args)
elif args.cmd == 'dec':
if (args.verbose > 0):
print("{}: Opening for decryption".format(args.input.name))
if args.output is None:
if ".encrypted." in basename(args.input.name):
file_out = basename(args.input.name).replace(".encrypted", "")
else:
file_out = os.path.splitext(basename(args.input.name))[0] + ".decrypted.bin"
args.output = open(file_out, 'wb')
unpack(args)
elif args.cmd == 'enc':
if (args.verbose > 0):
print("{}: Opening for encryption".format(args.input.name))
if args.output is None:
if ".decrypted." in basename(args.input.name):
file_out = basename(args.input.name).replace(".decrypted", "")
else:
file_out = os.path.splitext(basename(args.input.name))[0] + ".encrypted.bin"
args.output = open(file_out, 'wb')
pack(args)
else:
raise NotImplementedError("Unknown command: '{}'.".format(args.cmd))
if __name__ == '__main__':
try:
main()
except Exception as ex:
eprint("Error: "+str(ex))
if 0: raise
sys.exit(10)