borg/attic/key.py

315 lines
11 KiB
Python

from binascii import hexlify, a2b_base64, b2a_base64
from getpass import getpass
import os
import msgpack
import textwrap
import hmac
from hashlib import sha256
import zlib
from attic.crypto import pbkdf2_sha256, get_random_bytes, AES, bytes_to_long, long_to_bytes, bytes_to_int, num_aes_blocks
from attic.helpers import IntegrityError, get_keys_dir
PREFIX = b'\0' * 8
class HMAC(hmac.HMAC):
"""Workaround a bug in Python < 3.4 Where HMAC does not accept memoryviews
"""
def update(self, msg):
self.inner.update(msg)
def key_creator(repository, args):
if args.encryption == 'keyfile':
return KeyfileKey.create(repository, args)
elif args.encryption == 'passphrase':
return PassphraseKey.create(repository, args)
else:
return PlaintextKey.create(repository, args)
def key_factory(repository, manifest_data):
if manifest_data[0] == KeyfileKey.TYPE:
return KeyfileKey.detect(repository, manifest_data)
elif manifest_data[0] == PassphraseKey.TYPE:
return PassphraseKey.detect(repository, manifest_data)
elif manifest_data[0] == PlaintextKey.TYPE:
return PlaintextKey.detect(repository, manifest_data)
else:
raise Exception('Unkown Key type %d' % ord(manifest_data[0]))
class KeyBase(object):
def __init__(self):
self.TYPE_STR = bytes([self.TYPE])
def id_hash(self, data):
"""Return HMAC hash using the "id" HMAC key
"""
def encrypt(self, data):
pass
def decrypt(self, id, data):
pass
class PlaintextKey(KeyBase):
TYPE = 0x02
chunk_seed = 0
@classmethod
def create(cls, repository, args):
print('Encryption NOT enabled.\nUse the "--encryption=passphrase|keyfile" to enable encryption.')
return cls()
@classmethod
def detect(cls, repository, manifest_data):
return cls()
def id_hash(self, data):
return sha256(data).digest()
def encrypt(self, data):
return b''.join([self.TYPE_STR, zlib.compress(data)])
def decrypt(self, id, data):
if data[0] != self.TYPE:
raise IntegrityError('Invalid encryption envelope')
data = zlib.decompress(memoryview(data)[1:])
if id and sha256(data).digest() != id:
raise IntegrityError('Chunk id verification failed')
return data
class AESKeyBase(KeyBase):
"""Common base class shared by KeyfileKey and PassphraseKey
Chunks are encrypted using 256bit AES in Counter Mode (CTR)
Payload layout: TYPE(1) + HMAC(32) + NONCE(8) + CIPHERTEXT
To reduce payload size only 8 bytes of the 16 bytes nonce is saved
in the payload, the first 8 bytes are always zeros. This does not
affect security but limits the maximum repository capacity to
only 295 exabytes!
"""
PAYLOAD_OVERHEAD = 1 + 32 + 8 # TYPE + HMAC + NONCE
def id_hash(self, data):
"""Return HMAC hash using the "id" HMAC key
"""
return HMAC(self.id_key, data, sha256).digest()
def encrypt(self, data):
data = zlib.compress(data)
self.enc_cipher.reset()
data = b''.join((self.enc_cipher.iv[8:], self.enc_cipher.encrypt(data)))
hmac = HMAC(self.enc_hmac_key, data, sha256).digest()
return b''.join((self.TYPE_STR, hmac, data))
def decrypt(self, id, data):
if data[0] != self.TYPE:
raise IntegrityError('Invalid encryption envelope')
hmac = memoryview(data)[1:33]
if memoryview(HMAC(self.enc_hmac_key, memoryview(data)[33:], sha256).digest()) != hmac:
raise IntegrityError('Encryption envelope checksum mismatch')
self.dec_cipher.reset(iv=PREFIX + data[33:41])
data = zlib.decompress(self.dec_cipher.decrypt(data[41:])) # should use memoryview
if id and HMAC(self.id_key, data, sha256).digest() != id:
raise IntegrityError('Chunk id verification failed')
return data
def extract_nonce(self, payload):
if payload[0] != self.TYPE:
raise IntegrityError('Invalid encryption envelope')
nonce = bytes_to_long(payload[33:41])
return nonce
def init_from_random_data(self, data):
self.enc_key = data[0:32]
self.enc_hmac_key = data[32:64]
self.id_key = data[64:96]
self.chunk_seed = bytes_to_int(data[96:100])
# Convert to signed int32
if self.chunk_seed & 0x80000000:
self.chunk_seed = self.chunk_seed - 0xffffffff - 1
def init_ciphers(self, enc_iv=b''):
self.enc_cipher = AES(self.enc_key, enc_iv)
self.dec_cipher = AES(self.enc_key)
class PassphraseKey(AESKeyBase):
TYPE = 0x01
iterations = 100000
@classmethod
def create(cls, repository, args):
key = cls()
passphrase = os.environ.get('ATTIC_PASSPHRASE')
if passphrase is not None:
passphrase2 = passphrase
else:
passphrase, passphrase2 = 1, 2
while passphrase != passphrase2:
passphrase = getpass('Enter passphrase: ')
if not passphrase:
print('Passphrase must not be blank')
continue
passphrase2 = getpass('Enter same passphrase again: ')
if passphrase != passphrase2:
print('Passphrases do not match')
key.init(repository, passphrase)
if passphrase:
print('Remember your passphrase. Your data will be inaccessible without it.')
return key
@classmethod
def detect(cls, repository, manifest_data):
prompt = 'Enter passphrase for %s: ' % repository._location.orig
key = cls()
passphrase = os.environ.get('ATTIC_PASSPHRASE')
if passphrase is None:
passphrase = getpass(prompt)
while True:
key.init(repository, passphrase)
try:
key.decrypt(None, manifest_data)
num_blocks = num_aes_blocks(len(manifest_data) - 41)
key.init_ciphers(PREFIX + long_to_bytes(key.extract_nonce(manifest_data) + num_blocks))
return key
except IntegrityError:
passphrase = getpass(prompt)
def init(self, repository, passphrase):
self.init_from_random_data(pbkdf2_sha256(passphrase.encode('utf-8'), repository.id, self.iterations, 100))
self.init_ciphers()
class KeyfileKey(AESKeyBase):
FILE_ID = 'ATTIC KEY'
TYPE = 0x00
@classmethod
def detect(cls, repository, manifest_data):
key = cls()
path = cls.find_key_file(repository)
prompt = 'Enter passphrase for key file %s: ' % path
passphrase = os.environ.get('ATTIC_PASSPHRASE', '')
while not key.load(path, passphrase):
passphrase = getpass(prompt)
num_blocks = num_aes_blocks(len(manifest_data) - 41)
key.init_ciphers(PREFIX + long_to_bytes(key.extract_nonce(manifest_data) + num_blocks))
return key
@classmethod
def find_key_file(cls, repository):
id = hexlify(repository.id).decode('ascii')
keys_dir = get_keys_dir()
for name in os.listdir(keys_dir):
filename = os.path.join(keys_dir, name)
with open(filename, 'r') as fd:
line = fd.readline().strip()
if line and line.startswith(cls.FILE_ID) and line[10:] == id:
return filename
raise Exception('Key file for repository with ID %s not found' % id)
def load(self, filename, passphrase):
with open(filename, 'r') as fd:
cdata = a2b_base64(''.join(fd.readlines()[1:]).encode('ascii')) # .encode needed for Python 3.[0-2]
data = self.decrypt_key_file(cdata, passphrase)
if data:
key = msgpack.unpackb(data)
if key[b'version'] != 1:
raise IntegrityError('Invalid key file header')
self.repository_id = key[b'repository_id']
self.enc_key = key[b'enc_key']
self.enc_hmac_key = key[b'enc_hmac_key']
self.id_key = key[b'id_key']
self.chunk_seed = key[b'chunk_seed']
self.path = filename
return True
def decrypt_key_file(self, data, passphrase):
d = msgpack.unpackb(data)
assert d[b'version'] == 1
assert d[b'algorithm'] == b'sha256'
key = pbkdf2_sha256(passphrase.encode('utf-8'), d[b'salt'], d[b'iterations'], 32)
data = AES(key).decrypt(d[b'data'])
if HMAC(key, data, sha256).digest() != d[b'hash']:
return None
return data
def encrypt_key_file(self, data, passphrase):
salt = get_random_bytes(32)
iterations = 100000
key = pbkdf2_sha256(passphrase.encode('utf-8'), salt, iterations, 32)
hash = HMAC(key, data, sha256).digest()
cdata = AES(key).encrypt(data)
d = {
'version': 1,
'salt': salt,
'iterations': iterations,
'algorithm': 'sha256',
'hash': hash,
'data': cdata,
}
return msgpack.packb(d)
def save(self, path, passphrase):
key = {
'version': 1,
'repository_id': self.repository_id,
'enc_key': self.enc_key,
'enc_hmac_key': self.enc_hmac_key,
'id_key': self.id_key,
'chunk_seed': self.chunk_seed,
}
data = self.encrypt_key_file(msgpack.packb(key), passphrase)
with open(path, 'w') as fd:
fd.write('%s %s\n' % (self.FILE_ID, hexlify(self.repository_id).decode('ascii')))
fd.write('\n'.join(textwrap.wrap(b2a_base64(data).decode('ascii'))))
self.path = path
def change_passphrase(self):
passphrase, passphrase2 = 1, 2
while passphrase != passphrase2:
passphrase = getpass('New passphrase: ')
passphrase2 = getpass('Enter same passphrase again: ')
if passphrase != passphrase2:
print('Passphrases do not match')
self.save(self.path, passphrase)
print('Key file "%s" updated' % self.path)
@classmethod
def create(cls, repository, args):
filename = args.repository.to_key_filename()
path = filename
i = 1
while os.path.exists(path):
i += 1
path = filename + '.%d' % i
passphrase = os.environ.get('ATTIC_PASSPHRASE')
if passphrase is not None:
passphrase2 = passphrase
else:
passphrase, passphrase2 = 1, 2
while passphrase != passphrase2:
passphrase = getpass('Enter passphrase (empty for no passphrase):')
passphrase2 = getpass('Enter same passphrase again: ')
if passphrase != passphrase2:
print('Passphrases do not match')
key = cls()
key.repository_id = repository.id
key.init_from_random_data(get_random_bytes(100))
key.init_ciphers()
key.save(path, passphrase)
print('Key file "%s" created.' % key.path)
print('Keep this file safe. Your data will be inaccessible without it.')
return key