px4-firmware/Tools/decrypt_ulog.py

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#!/usr/bin/env python3
from Crypto.PublicKey import RSA
from Crypto.Cipher import PKCS1_OAEP
from Crypto.Cipher import ChaCha20
from Crypto.Hash import SHA256
import binascii
import argparse
#from pathlib import Path
import sys
if __name__ == "__main__":
parser = argparse.ArgumentParser(description="""CLI tool to decrypt an ulog file\n""")
parser.add_argument("ulog_file", help=".ulog file", nargs='?', default=None)
parser.add_argument("ulog_key", help=".ulogk, encrypted key", nargs='?', default=None)
parser.add_argument("rsa_key", help=".pem format key for decrypting the ulog key", nargs='?', default=None)
args = parser.parse_args()
# Only generate a key pair, don't sign
if not args.ulog_file or not args.ulog_key or not args.rsa_key:
print('Need all arguments, the encrypted ulog file, the key and the key decryption key')
sys.exit(1);
# Read the private RSA key to decrypt the cahcha key
with open(args.rsa_key, 'rb') as f:
r = RSA.importKey(f.read(), passphrase='')
# Read the encrypted xchacha key and the nonce
with open(args.ulog_key, 'rb') as f:
ulog_key_header = f.read(22)
# Parse the header
try:
# magic
if not ulog_key_header.startswith(bytearray("ULogKey".encode())):
raise Exception()
# version
if ulog_key_header[7] != 1:
raise Exception()
# expected key exchange algorithm (RSA_OAEP)
if ulog_key_header[16] != 4:
raise Exception()
key_size = ulog_key_header[19] << 8 | ulog_key_header[18];
nonce_size = ulog_key_header[21] << 8 | ulog_key_header[20];
ulog_key_cipher = f.read(key_size)
nonce = f.read(nonce_size)
except:
print("Keyfile format error")
sys.exit(1);
# Decrypt the xchacha key
cipher_rsa = PKCS1_OAEP.new(r,SHA256)
ulog_key = cipher_rsa.decrypt(ulog_key_cipher)
#print(binascii.hexlify(ulog_key))
# Read and decrypt the .ulgc
cipher = ChaCha20.new(key=ulog_key, nonce=nonce)
with open(args.ulog_file, 'rb') as f:
with open(args.ulog_file.rstrip(args.ulog_file[-1]), 'wb') as out:
out.write(cipher.decrypt(f.read()))