PySecretHandshake/secret_handshake/boxstream.py
2017-06-05 00:35:27 +02:00

102 lines
2.6 KiB
Python

import struct
from nacl.secret import SecretBox
from .util import bytes_to_long, long_to_bytes
NONCE_SIZE = 24
HEADER_LENGTH = 2 + 16 + 16
MAX_SEGMENT_SIZE = 4 * 1024
TERMINATION_HEADER = (b'\x00' * 18)
MAX_NONCE = (8 * NONCE_SIZE)
# TODO: Implement handling of messages > 4k
def inc_nonce(nonce):
num = bytes_to_long(nonce) + 1
if num > 2 ** MAX_NONCE:
num = 0
bnum = long_to_bytes(num)
bnum = b'\x00' * (NONCE_SIZE - len(bnum)) + bnum
return bnum
def get_stream_pair(reader, writer, **kwargs):
"""Return a tuple with `(unbox_stream, box_stream)` (reader/writer).
:return: (:class:`secret_handshake.boxstream.UnboxStream`,
:class:`secret_handshake.boxstream.BoxStream`) """
box_args = {
'key': kwargs['encrypt_key'],
'nonce': kwargs['encrypt_nonce'],
}
unbox_args = {
'key': kwargs['decrypt_key'],
'nonce': kwargs['decrypt_nonce'],
}
return UnboxStream(reader, **unbox_args), BoxStream(writer, **box_args)
class UnboxStream(object):
def __init__(self, reader, key, nonce):
self.reader = reader
self.key = key
self.nonce = nonce
self.closed = False
async def read(self):
data = await self.reader.read(HEADER_LENGTH)
if not data:
self.closed = True
return None
box = SecretBox(self.key)
header = box.decrypt(data, self.nonce)
if header == TERMINATION_HEADER:
self.closed = True
return None
length = struct.unpack('>H', header[:2])[0]
mac = header[2:]
data = await self.reader.read(length)
body = box.decrypt(mac + data, inc_nonce(self.nonce))
self.nonce = inc_nonce(inc_nonce(self.nonce))
return body
async def __aiter__(self):
while True:
data = await self.read()
if data is None:
return
yield data
class BoxStream(object):
def __init__(self, writer, key, nonce):
self.writer = writer
self.key = key
self.box = SecretBox(self.key)
self.nonce = nonce
def write(self, data):
# XXX: This nonce logic is almost for sure wrong
body = self.box.encrypt(data, inc_nonce(self.nonce))[24:]
header = struct.pack('>H', len(body) - 16) + body[:16]
hdrbox = self.box.encrypt(header, self.nonce)[24:]
self.writer.write(hdrbox)
self.nonce = inc_nonce(inc_nonce(self.nonce))
self.writer.write(body[16:])
def close(self):
self.writer.write(self.box.encrypt(b'\x00' * 18, self.nonce)[24:])