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