74a60a2e5b
SàT was using 16 bytes IV when sending files withr AES-GCM, due to ChatSecure being only compatible with that. Monal, an other iOS client is only compatible with 12 bytes IV, and ChatSecure has fixed its code to also handle 12 bytes IV, so there is not reason anymore to use 16 bytes, and SàT now uses 12 bytes.
252 lines
9.5 KiB
Python
252 lines
9.5 KiB
Python
#!/usr/bin/env python3
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# SàT plugin for handling AES-GCM file encryption
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# Copyright (C) 2009-2020 Jérôme Poisson (goffi@goffi.org)
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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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# 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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# You should have received a copy of the GNU Affero General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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import re
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from textwrap import dedent
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from functools import partial
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from urllib.parse import urlparse
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import mimetypes
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import secrets
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from cryptography.hazmat.primitives import ciphers
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from cryptography.hazmat.primitives.ciphers import modes
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from cryptography.hazmat import backends
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from cryptography.exceptions import AlreadyFinalized
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from urllib import parse
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import treq
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from sat.core.i18n import _
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from sat.core.constants import Const as C
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from sat.core import exceptions
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from sat.tools import stream
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from sat.core.log import getLogger
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log = getLogger(__name__)
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PLUGIN_INFO = {
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C.PI_NAME: "AES-GCM",
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C.PI_IMPORT_NAME: "AES-GCM",
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C.PI_TYPE: "SEC",
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C.PI_PROTOCOLS: ["OMEMO Media sharing"],
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C.PI_DEPENDENCIES: ["XEP-0363", "XEP-0384", "DOWNLOAD"],
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C.PI_MAIN: "AESGCM",
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C.PI_HANDLER: "no",
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C.PI_DESCRIPTION: dedent(_("""\
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Implementation of AES-GCM scheme, a way to encrypt files (not official XMPP standard).
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See https://xmpp.org/extensions/inbox/omemo-media-sharing.html for details
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""")),
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}
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AESGCM_RE = re.compile(
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r'aesgcm:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9'
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r'()@:%_\+.~#?&\/\/=]*)')
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class AESGCM(object):
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def __init__(self, host):
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self.host = host
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log.info(_("AESGCM plugin initialization"))
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host.plugins["DOWNLOAD"].registerScheme(
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"aesgcm", self.download
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)
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host.trigger.add("XEP-0363_upload_size", self._uploadSizeTrigger)
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host.trigger.add("XEP-0363_upload", self._uploadTrigger)
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host.trigger.add("messageReceived", self._messageReceivedTrigger)
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async def download(self, client, uri_parsed, dest_path, options):
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fragment = bytes.fromhex(uri_parsed.fragment)
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# legacy method use 16 bits IV, but OMEMO media sharing published spec indicates
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# which is 12 bits IV (AES-GCM spec recommandation), so we have to determine
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# which size has been used.
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if len(fragment) == 48:
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iv_size = 16
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elif len(fragment) == 44:
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iv_size = 12
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else:
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raise ValueError(
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f"Invalid URL fragment, can't decrypt file at {uri_parsed.get_url()}")
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iv, key = fragment[:iv_size], fragment[iv_size:]
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decryptor = ciphers.Cipher(
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ciphers.algorithms.AES(key),
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modes.GCM(iv),
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backend=backends.default_backend(),
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).decryptor()
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download_url = parse.urlunparse(
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('https', uri_parsed.netloc, uri_parsed.path, '', '', ''))
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head_data = await treq.head(download_url)
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content_length = int(head_data.headers.getRawHeaders('content-length')[0])
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# the 128 bits tag is put at the end
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file_size = content_length - 16
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file_obj = stream.SatFile(
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self.host,
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client,
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dest_path,
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mode="wb",
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size = file_size,
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)
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progress_id = file_obj.uid
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resp = await treq.get(download_url, unbuffered=True)
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d = treq.collect(resp, partial(
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self.onDataDownload,
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client=client,
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file_obj=file_obj,
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decryptor=decryptor))
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return progress_id, d
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def onDataDownload(self, data, client, file_obj, decryptor):
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if file_obj.tell() + len(data) > file_obj.size:
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# we're reaching end of file with this bunch of data
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# we may still have a last bunch if the tag is incomplete
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bytes_left = file_obj.size - file_obj.tell()
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if bytes_left > 0:
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decrypted = decryptor.update(data[:bytes_left])
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file_obj.write(decrypted)
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tag = data[bytes_left:]
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else:
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tag = data
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if len(tag) < 16:
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# the tag is incomplete, either we'll get the rest in next data bunch
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# or we have already the other part from last bunch of data
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try:
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# we store partial tag in decryptor._sat_tag
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tag = decryptor._sat_tag + tag
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except AttributeError:
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# no other part, we'll get the rest at next bunch
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decryptor.sat_tag = tag
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else:
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# we have the complete tag, it must be 128 bits
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if len(tag) != 16:
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raise ValueError(f"Invalid tag: {tag}")
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remain = decryptor.finalize_with_tag(tag)
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file_obj.write(remain)
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file_obj.close()
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else:
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decrypted = decryptor.update(data)
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file_obj.write(decrypted)
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def _uploadSizeTrigger(self, client, options, file_path, size, size_adjust):
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if options.get('encryption') != C.ENC_AES_GCM:
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return True
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# the tag is appended to the file
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size_adjust.append(16)
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return True
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def _encrypt(self, data, encryptor):
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if data:
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return encryptor.update(data)
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else:
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try:
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# end of file is reached, me must finalize
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ret = encryptor.finalize()
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tag = encryptor.tag
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return ret + tag
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except AlreadyFinalized:
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# as we have already finalized, we can now send EOF
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return b''
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def _uploadTrigger(self, client, options, sat_file, file_producer, slot):
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if options.get('encryption') != C.ENC_AES_GCM:
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return True
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log.debug("encrypting file with AES-GCM")
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iv = secrets.token_bytes(12)
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key = secrets.token_bytes(32)
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fragment = f'{iv.hex()}{key.hex()}'
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ori_url = parse.urlparse(slot.get)
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# we change the get URL with the one with aesgcm scheme and containing the
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# encoded key + iv
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slot.get = parse.urlunparse(['aesgcm', *ori_url[1:5], fragment])
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# encrypted data size will be bigger than original file size
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# so we need to check with final data length to avoid a warning on close()
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sat_file.check_size_with_read = True
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# file_producer get length directly from file, and this cause trouble has
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# we have to change the size because of encryption. So we adapt it here,
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# else the producer would stop reading prematurely
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file_producer.length = sat_file.size
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encryptor = ciphers.Cipher(
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ciphers.algorithms.AES(key),
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modes.GCM(iv),
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backend=backends.default_backend(),
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).encryptor()
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if sat_file.data_cb is not None:
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raise exceptions.InternalError(
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f"data_cb was expected to be None, it is set to {sat_file.data_cb}")
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# with data_cb we encrypt the file on the fly
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sat_file.data_cb = partial(self._encrypt, encryptor=encryptor)
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return True
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def _popAESGCMLinks(self, match, links):
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link = match.group()
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if link not in links:
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links.append(link)
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return ""
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def _checkAESGCMAttachments(self, client, data):
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if not data.get('message'):
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return data
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links = []
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for lang, message in list(data['message'].items()):
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message = AESGCM_RE.sub(
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partial(self._popAESGCMLinks, links=links),
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message)
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if links:
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message = message.strip()
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if not message:
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del data['message'][lang]
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else:
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data['message'][lang] = message
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mess_encrypted = client.encryption.isEncrypted(data)
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attachments = data['extra'].setdefault(C.MESS_KEY_ATTACHMENTS, [])
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for link in links:
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path = urlparse(link).path
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attachment = {
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"url": link,
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}
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media_type = mimetypes.guess_type(path, strict=False)[0]
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if media_type is not None:
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attachment[C.MESS_KEY_MEDIA_TYPE] = media_type
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if mess_encrypted:
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# we don't add the encrypted flag if the message itself is not
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# encrypted, because the decryption key is part of the link,
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# so sending it over unencrypted channel is like having no
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# encryption at all.
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attachment['encrypted'] = True
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attachments.append(attachment)
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return data
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def _messageReceivedTrigger(self, client, message_elt, post_treat):
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# we use a post_treat callback instead of "message_parse" trigger because we need
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# to check if the "encrypted" flag is set to decide if we add the same flag to the
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# attachment
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post_treat.addCallback(partial(self._checkAESGCMAttachments, client))
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return True
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