256 lines
9.9 KiB
Python
256 lines
9.9 KiB
Python
# cryptomator-utils: Python utilities for inspecting Cryptomator drives
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# Copyright (C) 2024 Lee Yingtong Li (RunasSudo)
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU Affero General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU Affero General Public License for more details.
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#
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# You should have received a copy of the GNU Affero General Public License
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# along with this program. If not, see <https://www.gnu.org/licenses/>.
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from .aes import aes_siv_decrypt, aes_siv_encrypt
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from .b64url import b64url_decode, b64url_encode
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from Crypto.Cipher import AES
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from cryptography.hazmat.primitives.kdf.scrypt import Scrypt
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from cryptography.hazmat.primitives.keywrap import aes_key_unwrap, InvalidUnwrap
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import base64
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import getpass
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import hashlib
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import hmac
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import json
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import os
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import struct
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import sys
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def load_vault_config(vault_config_path):
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"""
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Load and verify a vault.cryptomator configuration file and associated master key
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Returns (primary_master_key, hmac_master_key)
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"""
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# ------------------
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# Parse vault config
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with open(vault_config_path, 'r') as vault_config_file:
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vault_config_data = vault_config_file.read()
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# Split JWT header, payload and signature
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vault_config_jwt_parts = vault_config_data.split('.')
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if len(vault_config_jwt_parts) != 3:
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print('Error: Invalid JWT (got {} parts, expected 3)'.format(len(vault_config_jwt_parts)))
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sys.exit(1)
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# Parse JWT header and payload
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try:
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vault_config_header = json.loads(b64url_decode(vault_config_jwt_parts[0]).decode('utf-8'))
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vault_config_payload = json.loads(b64url_decode(vault_config_jwt_parts[1]).decode('utf-8'))
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except json.JSONDecodeError as ex:
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print('Error: Malformed JWT (invalid JSON)')
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import traceback; traceback.print_exc()
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sys.exit(1)
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# Validate settings
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if vault_config_header['typ'] != 'JWT':
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print('Error: Malformed JWT (no "typ" in header)')
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sys.exit(1)
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if vault_config_header['alg'] != 'HS256':
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print('Error: Unsupported JWT algorithm (got {}, expected HS256)'.format(vault_config_header['alg']))
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sys.exit(1)
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if vault_config_payload['format'] != 8: # Current Cryptomator vault format
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print('Error: Unsupported vault format (got {}, expected 8)'.format(vault_config_payload['format']))
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sys.exit(1)
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if vault_config_payload['cipherCombo'] != 'SIV_GCM':
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print('Error: Unsupported vault cipher mode (got {}, expected SIV_GCM)'.format(vault_config_payload['cipherCombo']))
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sys.exit(1)
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# -------------
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# Read key file
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if not vault_config_header['kid'].startswith('masterkeyfile:'):
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print('Error: Unsupported vault master key ID (got {}, expected masterkeyfile)'.format(vault_config_header['kid']))
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sys.exit(1)
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master_key_path = os.path.join(os.path.split(vault_config_path)[0], vault_config_header['kid'][len('masterkeyfile:'):])
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with open(master_key_path, 'r') as master_key_file:
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master_key_config = json.load(master_key_file)
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# ----------
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# Derive KEK
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master_password = getpass.getpass()
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kek = Scrypt(
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base64.b64decode(master_key_config['scryptSalt']),
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32, # Masterkey.SUBKEY_LEN_BYTES in cryptolib
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master_key_config['scryptCostParam'],
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master_key_config['scryptBlockSize'],
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1 # Scrypt.P in cryptolib
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).derive(master_password.encode('utf-8'))
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# -----------------------------------------
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# Unwrap encryption keys using AES Key Wrap
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try:
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primary_master_key = aes_key_unwrap(kek, base64.b64decode(master_key_config['primaryMasterKey']))
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hmac_master_key = aes_key_unwrap(kek, base64.b64decode(master_key_config['hmacMasterKey']))
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except InvalidUnwrap:
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print('Error: Incorrect password')
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sys.exit(1)
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# -------------------------------
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# Validate vault config signature
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# HMAC secret is the combined "masterkey" (primary_master_key + hmac_master_key) - see Masterkey class in cryptolib
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expected_signature = hmac.digest(primary_master_key + hmac_master_key, (vault_config_jwt_parts[0] + '.' + vault_config_jwt_parts[1]).encode('utf-8'), 'SHA256')
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if b64url_encode(expected_signature) != vault_config_jwt_parts[2]:
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print('Error: Invalid vault configuration file signature')
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sys.exit(1)
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return primary_master_key, hmac_master_key
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def hash_directory_id(primary_master_key, hmac_master_key, directory_id):
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"""
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Compute a hashed encrypted directory ID for the given plaintext directory ID
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"""
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# Directory ID is encrypted with AES-SIV and hashed
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encrypted_directory_id = aes_siv_encrypt(primary_master_key, hmac_master_key, directory_id.encode('utf-8'), None)
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hashed_directory_id = base64.b32encode(hashlib.sha1(encrypted_directory_id).digest()).decode('utf-8')
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return hashed_directory_id
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def directory_path_to_id(vault_path, primary_master_key, hmac_master_key, directory_path):
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"""
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Recurse the drive to resolve the directory ID for the directory at the given plaintext path
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"""
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directory_path_parts = directory_path.strip('/').split('/')
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# Begin in root directory
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# The root directory in Cryptomator has an empty directory ID
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directory_id = ''
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# Traverse path
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for path_part in directory_path_parts:
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if not path_part:
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continue
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# Hash the current directory ID
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hashed_directory_id = hash_directory_id(primary_master_key, hmac_master_key, directory_id)
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# Look up the encrypted path_part in the current directory
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encrypted_filename = encrypt_filename(primary_master_key, hmac_master_key, directory_id, path_part)
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# Get the directory ID of the part_path
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subdirectory_dir_file = os.path.join(vault_path, 'd', hashed_directory_id[:2], hashed_directory_id[2:], encrypted_filename, 'dir.c9r')
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with open(subdirectory_dir_file, 'r') as f:
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new_directory_id = f.read()
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# Traverse to the new directory ID
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directory_id = new_directory_id
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return directory_id
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def list_directory(vault_path, primary_master_key, hmac_master_key, directory_id):
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"""
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Return a list of files and directories in the directory with the given plaintext directory ID
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"""
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hashed_directory_id = hash_directory_id(primary_master_key, hmac_master_key, directory_id)
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# Check directory ID given by dirid.c9r matches the expected directory ID
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stored_directory_id = decrypt_file(vault_path, primary_master_key, hashed_directory_id, 'dirid.c9r')
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if stored_directory_id != directory_id.encode('utf-8'):
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print('Error: Unexpected dirid.c9r (got "{}", expected "{}")'.format(stored_directory_id.decode('utf-8'), directory_id))
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sys.exit(1)
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# List directory contents
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directory_contents = []
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for entry in os.scandir(os.path.join(vault_path, 'd', hashed_directory_id[:2], hashed_directory_id[2:])):
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if entry.name == 'dirid.c9r':
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continue
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elif entry.name.endswith('.c9r'):
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directory_contents.append(decrypt_filename(primary_master_key, hmac_master_key, directory_id, entry.name))
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elif entry.name.endswith('.c9s'):
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print('Warning: Unsupported entry with long filename "{}" - not yet implemented'.format(entry.name))
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else:
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print('Warning: Unknown file "{}" - ignoring'.format(entry.name))
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return directory_contents
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def encrypt_filename(primary_master_key, hmac_master_key, directory_id, filename):
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"""
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Return the encrypted filename for a given plaintext filename within a directory with the given plaintext directory ID
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"""
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# Filename is encrypted with AES-SIV, passing the plaintext directory ID as AAD
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return b64url_encode(aes_siv_encrypt(primary_master_key, hmac_master_key, filename.encode('utf-8'), [directory_id.encode('utf-8')]), strip_padding=False) + '.c9r'
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def decrypt_filename(primary_master_key, hmac_master_key, directory_id, encrypted_filename):
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"""
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Return the plaintext filename for a given encrypted filename within a directory with the given plaintext directory ID
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"""
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if not encrypted_filename.endswith('.c9r'):
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raise ValueError('Encrypted filename must end with .c9r')
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# Reverse the AES-SIV encryption, passing the plaintext directory ID as AAD
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ciphertext_filename = b64url_decode(encrypted_filename[:-len('.c9r')])
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plaintext_filename = aes_siv_decrypt(primary_master_key, hmac_master_key, ciphertext_filename, [directory_id.encode('utf-8')]).decode('utf-8')
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return plaintext_filename
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def decrypt_file(vault_path, primary_master_key, hashed_directory_id, filename):
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"""
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Return the decrypted contents of the file given by the plaintext filename and hashed directory ID
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"""
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# Read the encrypted contents
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encrypted_file_path = os.path.join(vault_path, 'd', hashed_directory_id[:2], hashed_directory_id[2:], filename)
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with open(encrypted_file_path, 'rb') as f:
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ciphertext = f.read()
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# Read header
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ciphertext_header = ciphertext[:68]
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header_nonce = ciphertext_header[:12]
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header_payload = ciphertext_header[12:-16]
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header_tag = ciphertext_header[-16:]
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# Decrypt header to obtain the content key
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cipher = AES.new(primary_master_key, AES.MODE_GCM, nonce=header_nonce)
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plaintext_header = cipher.decrypt_and_verify(header_payload, header_tag)
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content_key = plaintext_header[8:]
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# Decrypt file in chunks corresponding to 32 KiB plaintext
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plaintext = bytearray()
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for chunk_num, idx in enumerate(range(68, len(ciphertext), 32*1024 + 28)): # Skip 68 byte header; each encrypted chunk is 32 KiB + 28 byte overhead
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ciphertext_chunk = ciphertext[idx:idx+32*1024+28]
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chunk_nonce = ciphertext_chunk[:12]
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chunk_payload = ciphertext_chunk[12:-16]
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chunk_tag = ciphertext_chunk[-16:]
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# Chunk is encrypted with AES-GCM
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cipher = AES.new(content_key, AES.MODE_GCM, nonce=chunk_nonce)
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# Chunk number and header nonce are passed as AAD
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# Contrary to the Cryptomator documentation, chunk number is a 64-bit not 32-bit integer - https://github.com/cryptomator/docs/pull/54
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cipher.update(struct.pack('>Q', chunk_num))
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cipher.update(header_nonce)
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plaintext_chunk = cipher.decrypt_and_verify(chunk_payload, chunk_tag)
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plaintext.extend(plaintext_chunk)
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return bytes(plaintext)
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