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# -*- coding: utf-8 -*-
# _crypto.py
# Copyright (C) 2016 LEAP Encryption Access Project
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
"""
Cryptographic operations for the soledad client.
This module implements streaming crypto operations.
It replaces the old client.crypto module, that will be deprecated in soledad
0.12.
The algorithm for encryptig and decrypting is as follow:
The KEY is a 32 bytes value.
The PREAMBLE is a packed_structure with encryption metadata.
The SEPARATOR is a space.
Encryption
----------
ciphertext = b64_encode(packed_preamble)
+ SEPARATOR
+ b64(AES_GCM(ciphertext) + tag)
Decryption
----------
PREAMBLE + SEPARATOR + PAYLOAD
Ciphertext and Tag CAN be encoded in b64 (armor=True) or raw (False)
check_preamble(b64_decode(ciphertext.split(SEPARATOR)[0])
PAYLOAD = ciphertext + tag
decrypt(PAYLOAD)
"""
import base64
import hashlib
import warnings
import hmac
import os
import struct
import time
from io import BytesIO
from collections import namedtuple
from twisted.internet import defer
from twisted.internet import interfaces
from twisted.web.client import FileBodyProducer
from cryptography.exceptions import InvalidTag
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.backends.multibackend import MultiBackend
from cryptography.hazmat.backends.openssl.backend \
import Backend as OpenSSLBackend
from zope.interface import implementer
SECRET_LENGTH = 64
SEPARATOR = ' '
CRYPTO_BACKEND = MultiBackend([OpenSSLBackend()])
PACMAN = struct.Struct('2sbbQ16s255p255pQ')
LEGACY_PACMAN = struct.Struct('2sbbQ16s255p255p')
BLOB_SIGNATURE_MAGIC = '\x13\x37'
ENC_SCHEME = namedtuple('SCHEME', 'symkey')(1)
ENC_METHOD = namedtuple('METHOD', 'aes_256_ctr aes_256_gcm')(1, 2)
DocInfo = namedtuple('DocInfo', 'doc_id rev')
class EncryptionDecryptionError(Exception):
pass
class InvalidBlob(Exception):
pass
class SoledadCrypto(object):
"""
This class provides convenient methods for document encryption and
decryption using BlobEncryptor and BlobDecryptor classes.
"""
def __init__(self, secret):
"""
Initialize the crypto object.
:param secret: The Soledad remote storage secret.
:type secret: str
"""
self.secret = secret
def encrypt_doc(self, doc):
"""
Creates and configures a BlobEncryptor, asking it to start encryption
and wrapping the result as a simple JSON string with a "raw" key.
:param doc: the document to be encrypted.
:type doc: SoledadDocument
:return: A deferred whose callback will be invoked with a JSON string
containing the ciphertext as the value of "raw" key.
:rtype: twisted.internet.defer.Deferred
"""
def put_raw(blob):
raw = blob.getvalue()
return '{"raw": "' + raw + '"}'
content = BytesIO(str(doc.get_json()))
info = DocInfo(doc.doc_id, doc.rev)
del doc
encryptor = BlobEncryptor(info, content, secret=self.secret)
d = encryptor.encrypt()
d.addCallback(put_raw)
return d
def decrypt_doc(self, doc):
"""
Creates and configures a BlobDecryptor, asking it decrypt and returning
the decrypted cleartext content from the encrypted document.
:param doc: the document to be decrypted.
:type doc: SoledadDocument
:return: The decrypted cleartext content of the document.
:rtype: str
"""
info = DocInfo(doc.doc_id, doc.rev)
ciphertext = BytesIO()
payload = doc.content['raw']
del doc
ciphertext.write(str(payload))
decryptor = BlobDecryptor(info, ciphertext, secret=self.secret)
return decryptor.decrypt()
def encrypt_sym(data, key, method=ENC_METHOD.aes_256_gcm):
"""
Encrypt data using AES-256 cipher in selected mode.
:param data: The data to be encrypted.
:type data: str
:param key: The key used to encrypt data (must be 256 bits long).
:type key: str
:return: A tuple with the initialization vector and the ciphertext, both
encoded as base64.
:rtype: (str, str)
"""
mode = _mode_by_method(method)
encryptor = AESWriter(key, mode=mode)
encryptor.write(data)
_, ciphertext = encryptor.end()
iv = base64.b64encode(encryptor.iv)
tag = encryptor.tag or ''
return iv, ciphertext + tag
def decrypt_sym(data, key, iv, method=ENC_METHOD.aes_256_gcm):
"""
Decrypt data using AES-256 cipher in selected mode.
:param data: The data to be decrypted.
:type data: str
:param key: The symmetric key used to decrypt data (must be 256 bits
long).
:type key: str
:param iv: The base64 encoded initialization vector.
:type iv: str
:return: The decrypted data.
:rtype: str
"""
_iv = base64.b64decode(str(iv))
mode = _mode_by_method(method)
tag = None
if mode == modes.GCM:
data, tag = data[:-16], data[-16:]
decryptor = AESWriter(key, _iv, tag=tag, mode=mode)
decryptor.write(data)
_, plaintext = decryptor.end()
return plaintext
# TODO maybe rename this to Encryptor, since it will be used by blobs an non
# blobs in soledad.
class BlobEncryptor(object):
"""
Produces encrypted data from the cleartext data associated with a given
SoledadDocument using AES-256 cipher in GCM mode.
The production happens using a Twisted's FileBodyProducer, which uses a
Cooperator to schedule calls and can be paused/resumed. Each call takes at
most 65536 bytes from the input.
Both the production input and output are file descriptors, so they can be
applied to a stream of data.
"""
# TODO
# This class needs further work to allow for proper streaming.
# RIght now we HAVE TO WAIT until the end of the stream before encoding the
# result. It should be possible to do that just encoding the chunks and
# passing them to a sink, but for that we have to encode the chunks at
# proper alignment (3 byes?) with b64 if armor is defined.
def __init__(self, doc_info, content_fd, secret=None, armor=True,
sink=None):
if not secret:
raise EncryptionDecryptionError('no secret given')
self.doc_id = doc_info.doc_id
self.rev = doc_info.rev
self.armor = armor
self._content_fd = content_fd
self._content_size = self._get_size(content_fd)
self._producer = FileBodyProducer(content_fd, readSize=2**16)
self.sym_key = _get_sym_key_for_doc(doc_info.doc_id, secret)
self._aes = AESWriter(self.sym_key, _buffer=sink)
self._aes.authenticate(self._encode_preamble())
def _get_size(self, fd):
fd.seek(0, os.SEEK_END)
size = _ceiling(fd.tell())
fd.seek(0)
return size
@property
def iv(self):
return self._aes.iv
@property
def tag(self):
return self._aes.tag
def encrypt(self):
"""
Starts producing encrypted data from the cleartext data.
:return: A deferred which will be fired when encryption ends and whose
callback will be invoked with the resulting ciphertext.
:rtype: twisted.internet.defer.Deferred
"""
# XXX pass a sink to aes?
d = self._producer.startProducing(self._aes)
d.addCallback(lambda _: self._end_crypto_stream_and_encode_result())
return d
def _encode_preamble(self):
current_time = int(time.time())
preamble = PACMAN.pack(
BLOB_SIGNATURE_MAGIC,
ENC_SCHEME.symkey,
ENC_METHOD.aes_256_gcm,
current_time,
self.iv,
str(self.doc_id),
str(self.rev),
self._content_size)
return preamble
def _end_crypto_stream_and_encode_result(self):
# TODO ---- this needs to be refactored to allow PROPER streaming
# We should write the preamble as soon as possible,
# Is it possible to write the AES stream as soon as it is encrypted by
# chunks?
# FIXME also, it needs to be able to encode chunks with base64 if armor
preamble, encrypted = self._aes.end()
result = BytesIO()
result.write(
base64.urlsafe_b64encode(preamble))
result.write(SEPARATOR)
if self.armor:
result.write(
base64.urlsafe_b64encode(encrypted + self.tag))
else:
result.write(encrypted)
result.write(self.tag)
result.seek(0)
return defer.succeed(result)
class CryptoStreamBodyProducer(FileBodyProducer):
"""
A BodyProducer that gets the tag from the last 16 bytes before closing the
fd.
"""
_tag = None
@property
def tag(self):
# XXX this is a bit tricky. If you call this
# before the end of the stream, you will ruin everything
if not self._tag:
self._writeTag()
return self._tag
def _writeTag(self):
fd = self._inputFile
fd.seek(-16, os.SEEK_END)
self._tag = fd.read(16)
fd.seek(0)
def stopProducing(self):
self._writeTag()
self._inputFile.close()
self._task.stop()
def _writeloop(self, consumer):
"""
Return an iterator which reads one chunk of bytes from the input file
and writes them to the consumer for each time it is iterated.
"""
while True:
bytes = self._inputFile.read(self._readSize)
if not bytes:
self._writeTag()
self._inputFile.close()
break
consumer.write(base64.urlsafe_b64decode(bytes))
yield None
# TODO maybe rename this to just Decryptor, since it will be used by blobs
# and non blobs in soledad.
class BlobDecryptor(object):
"""
Decrypts an encrypted blob associated with a given Document.
Will raise an exception if the blob doesn't have the expected structure, or
if the GCM tag doesn't verify.
"""
# TODO enable the ascii armor = False
def __init__(self, doc_info, ciphertext_fd, result=None,
secret=None, armor=True, start_stream=True):
if not secret:
raise EncryptionDecryptionError('no secret given')
if armor is False:
raise NotImplementedError
self.doc_id = doc_info.doc_id
self.rev = doc_info.rev
self.fd = ciphertext_fd
self.armor = armor
self._producer = None
self.size = None
preamble, iv = self._consume_preamble()
assert preamble
assert iv
self.result = result or BytesIO()
sym_key = _get_sym_key_for_doc(doc_info.doc_id, secret)
self._aes = AESWriter(sym_key, iv, self.result, tag=None)
self._aes.authenticate(preamble)
if start_stream:
self._start_stream()
def _start_stream(self):
self._producer = CryptoStreamBodyProducer(self.fd, readSize=2**16)
self._producer.armor = self.armor
def _consume_preamble(self):
self.fd.seek(0)
try:
parts = self.fd.getvalue().split()
encoded_preamble = parts[0]
preamble = base64.urlsafe_b64decode(encoded_preamble)
except (TypeError, ValueError):
raise InvalidBlob
try:
if len(preamble) == LEGACY_PACMAN.size:
warnings.warn("Decrypting a legacy document without size. " +
"This will be deprecated in 0.12. Doc was: " +
"doc_id: %s rev: %s" % (self.doc_id, self.rev),
Warning)
unpacked_data = LEGACY_PACMAN.unpack(preamble)
magic, sch, meth, ts, iv, doc_id, rev = unpacked_data
elif len(preamble) == PACMAN.size:
unpacked_data = PACMAN.unpack(preamble)
magic, sch, meth, ts, iv, doc_id, rev, doc_size = unpacked_data
self.size = doc_size
else:
raise InvalidBlob("Unexpected preamble size %d", len(preamble))
except struct.error as e:
raise InvalidBlob(e)
if magic != BLOB_SIGNATURE_MAGIC:
raise InvalidBlob
# TODO check timestamp. Just as a sanity check, but for instance
# we can refuse to process something that is in the future or
# too far in the past (1984 would be nice, hehe)
if sch != ENC_SCHEME.symkey:
raise InvalidBlob('invalid scheme')
if meth != ENC_METHOD.aes_256_gcm:
raise InvalidBlob('invalid encryption scheme')
if rev != self.rev:
raise InvalidBlob('invalid revision')
if doc_id != self.doc_id:
raise InvalidBlob('invalid doc id')
self.fd.seek(0)
tail = ''.join(parts[1:])
self.fd.write(tail)
self.fd.seek(len(tail))
self.fd.truncate()
self.fd.seek(0)
return preamble, iv
def _end_stream(self):
try:
self._aes.end()[1]
except InvalidTag:
raise InvalidBlob('Invalid Tag. Blob authentication failed.')
fd = self.result
fd.seek(-16, os.SEEK_END)
fd.truncate()
fd.seek(0)
return self.result
def decrypt(self):
"""
Starts producing encrypted data from the cleartext data.
:return: A deferred which will be fired when encryption ends and whose
callback will be invoked with the resulting ciphertext.
:rtype: twisted.internet.defer.Deferred
"""
d = self.startProducing()
d.addCallback(lambda _: self._end_stream())
return d
def startProducing(self):
if not self._producer:
self._start_stream()
return self._producer.startProducing(self._aes)
def endStream(self):
self._end_stream()
def write(self, data):
self._aes.write(data)
def close(self):
result = self._aes.end()
return result
@implementer(interfaces.IConsumer)
class AESWriter(object):
"""
A Twisted's Consumer implementation that takes an input file descriptor and
applies AES-256 cipher in GCM mode.
It is used both for encryption and decryption of a stream, depending of the
value of the tag parameter. If you pass a tag, it will operate in
decryption mode, authenticating the preamble. If no tag is passed,
encryption mode is assumed.
"""
def __init__(self, key, iv=None, _buffer=None, tag=None, mode=modes.GCM):
if len(key) != 32:
raise EncryptionDecryptionError('key is not 256 bits')
if tag is not None:
# if tag, we're decrypting
assert iv is not None
self.iv = iv or os.urandom(16)
self.buffer = _buffer or BytesIO()
cipher = _get_aes_cipher(key, self.iv, tag, mode)
cipher = cipher.decryptor() if tag else cipher.encryptor()
self.cipher, self.aead = cipher, ''
def authenticate(self, data):
self.aead += data
self.cipher.authenticate_additional_data(data)
@property
def tag(self):
return getattr(self.cipher, 'tag', None)
def write(self, data):
self.buffer.write(self.cipher.update(data))
def end(self):
self.buffer.write(self.cipher.finalize())
return self.aead, self.buffer.getvalue()
def is_symmetrically_encrypted(content):
"""
Returns True if the document was symmetrically encrypted.
'EzcB' is the base64 encoding of \x13\x37 magic number and 1 (symmetrically
encrypted value for enc_scheme flag).
:param doc: The document content as string
:type doc: str
:rtype: bool
"""
sym_signature = '{"raw": "EzcB'
return content and content.startswith(sym_signature)
# utils
def _hmac_sha256(key, data):
return hmac.new(key, data, hashlib.sha256).digest()
def _get_sym_key_for_doc(doc_id, secret):
key = secret[SECRET_LENGTH:]
return _hmac_sha256(key, doc_id)
def _get_aes_cipher(key, iv, tag, mode=modes.GCM):
mode = mode(iv, tag) if mode == modes.GCM else mode(iv)
return Cipher(algorithms.AES(key), mode, backend=CRYPTO_BACKEND)
def _mode_by_method(method):
if method == ENC_METHOD.aes_256_gcm:
return modes.GCM
else:
return modes.CTR
def _ceiling(size):
"""
Some simplistic ceiling scheme that uses powers of 2.
We report everything below 4096 bytes as that minimum threshold.
See #8759 for research pending for less simplistic/aggresive strategies.
"""
for i in xrange(12, 31):
step = 2 ** i
if size < step:
return step
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