2022-02-23 14:07:13 +00:00
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# Mobile Verification Toolkit (MVT)
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# Copyright (c) 2021-2022 The MVT Project Authors.
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# Use of this software is governed by the MVT License 1.1 that can be found at
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# https://license.mvt.re/1.1/
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2022-03-10 10:33:54 +00:00
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import datetime
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import io
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import json
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import tarfile
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import zlib
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from cryptography.hazmat.primitives import hashes, padding
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from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
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from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC
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from mvt.common.utils import check_for_links, convert_timestamp_to_iso
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PBKDF2_KEY_SIZE = 32
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class AndroidBackupParsingError(Exception):
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"""Exception raised file parsing an android backup file"""
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class AndroidBackupNotImplemented(AndroidBackupParsingError):
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pass
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class InvalidBackupPassword(AndroidBackupParsingError):
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pass
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def to_utf8_bytes(input_bytes):
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output = []
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for byte in input_bytes:
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if byte < ord(b'\x80'):
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output.append(byte)
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else:
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output.append(ord('\xef') | (byte >> 12))
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output.append(ord('\xbc') | ((byte >> 6) & ord('\x3f')))
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output.append(ord('\x80') | (byte & ord('\x3f')))
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return bytes(output)
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def parse_ab_header(data):
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"""
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Parse the header of an Android Backup file
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Returns a dict {'backup': True, 'compression': False,
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'encryption': "none", 'version': 4}
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"""
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if data.startswith(b"ANDROID BACKUP"):
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[magic_header, version, is_compressed, encryption, tar_data] = data.split(b"\n", 4)
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return {
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"backup": True,
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"compression": (is_compressed == b"1"),
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"version": int(version),
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"encryption": encryption.decode("utf-8")
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}
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return {
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"backup": False,
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"compression": None,
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"version": None,
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"encryption": None
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}
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def decrypt_master_key(password, user_salt, user_iv, pbkdf2_rounds, master_key_blob, format_version, checksum_salt):
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"""Generate AES key from user password uisng PBKDF2
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The backup master key is extracted from the master key blog after decryption.
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"""
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# Derive key from password using PBKDF2
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kdf = PBKDF2HMAC(algorithm=hashes.SHA1(), length=32, salt=user_salt, iterations=pbkdf2_rounds)
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key = kdf.derive(password.encode("utf-8"))
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# Decrypt master key blob
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cipher = Cipher(algorithms.AES(key), modes.CBC(user_iv))
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decryptor = cipher.decryptor()
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try:
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decryted_master_key_blob = decryptor.update(master_key_blob) + decryptor.finalize()
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# Extract key and IV from decrypted blob.
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key_blob = io.BytesIO(decryted_master_key_blob)
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master_iv_length = ord(key_blob.read(1))
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master_iv = key_blob.read(master_iv_length)
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master_key_length = ord(key_blob.read(1))
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master_key = key_blob.read(master_key_length)
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master_key_checksum_length = ord(key_blob.read(1))
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master_key_checksum = key_blob.read(master_key_checksum_length)
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except TypeError:
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raise InvalidBackupPassword()
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# Handle quirky encoding of master key bytes in Android original Java crypto code
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if format_version > 1:
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hmac_mk = to_utf8_bytes(master_key)
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else:
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hmac_mk = master_key
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# Derive checksum to confirm successful backup decryption.
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kdf = PBKDF2HMAC(algorithm=hashes.SHA1(), length=32, salt=checksum_salt, iterations=pbkdf2_rounds)
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calculated_checksum = kdf.derive(hmac_mk)
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if master_key_checksum != calculated_checksum:
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raise InvalidBackupPassword()
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return master_key, master_iv
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def decrypt_backup_data(encrypted_backup, password, encryption_algo, format_version):
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"""
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Generate encryption keyffrom password and do decryption
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"""
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if encryption_algo != b"AES-256":
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raise AndroidBackupNotImplemented("Encryption Algorithm not implemented")
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if password is None:
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raise InvalidBackupPassword()
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[user_salt, checksum_salt, pbkdf2_rounds, user_iv, master_key_blob, encrypted_data] = encrypted_backup.split(b"\n", 5)
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user_salt = bytes.fromhex(user_salt.decode("utf-8"))
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checksum_salt = bytes.fromhex(checksum_salt.decode("utf-8"))
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pbkdf2_rounds = int(pbkdf2_rounds)
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user_iv = bytes.fromhex(user_iv.decode("utf-8"))
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master_key_blob = bytes.fromhex(master_key_blob.decode("utf-8"))
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# Derive decryption master key from password
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master_key, master_iv = decrypt_master_key(password=password, user_salt=user_salt, user_iv=user_iv,
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pbkdf2_rounds=pbkdf2_rounds, master_key_blob=master_key_blob,
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format_version=format_version, checksum_salt=checksum_salt)
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# Decrypt and unpad backup data using derivied key
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cipher = Cipher(algorithms.AES(master_key), modes.CBC(master_iv))
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decryptor = cipher.decryptor()
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decrypted_tar = decryptor.update(encrypted_data) + decryptor.finalize()
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unpadder = padding.PKCS7(128).unpadder()
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return unpadder.update(decrypted_tar)
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def parse_backup_file(data, password=None):
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"""
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Parse an ab file, returns a tar file
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"""
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if not data.startswith(b"ANDROID BACKUP"):
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raise AndroidBackupParsingError("Invalid file header")
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[magic_header, version, is_compressed, encryption_algo, tar_data] = data.split(b"\n", 4)
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version = int(version)
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is_compressed = int(is_compressed)
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if encryption_algo != b"none":
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tar_data = decrypt_backup_data(tar_data, password, encryption_algo, format_version=version)
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if is_compressed:
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try:
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tar_data = zlib.decompress(tar_data)
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except zlib.error:
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raise AndroidBackupParsingError("Impossible to decompress the backup file")
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return tar_data
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def parse_tar_for_sms(data):
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"""
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Extract SMS from a tar backup archive
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Returns an array of SMS
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"""
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dbytes = io.BytesIO(data)
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tar = tarfile.open(fileobj=dbytes)
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try:
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member = tar.getmember("apps/com.android.providers.telephony/d_f/000000_sms_backup")
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except KeyError:
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return []
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dhandler = tar.extractfile(member)
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return parse_sms_file(dhandler.read())
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def parse_sms_file(data):
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"""
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Parse an SMS file extracted from a folder
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Returns a list of SMS entries
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"""
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res = []
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data = zlib.decompress(data)
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json_data = json.loads(data)
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for entry in json_data:
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message_links = check_for_links(entry["body"])
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utc_timestamp = datetime.datetime.utcfromtimestamp(int(entry["date"]) / 1000)
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entry["isodate"] = convert_timestamp_to_iso(utc_timestamp)
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entry["direction"] = ("sent" if int(entry["date_sent"]) else "received")
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# If we find links in the messages or if they are empty we add them to the list.
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if message_links or entry["body"].strip() == "":
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entry["links"] = message_links
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res.append(entry)
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return res
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