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import struct
from asyncio import IncompleteReadError
from async_generator import async_generator, yield_
from nacl.secret import SecretBox
from .util import inc_nonce, split_chunks
HEADER_LENGTH = 2 + 16 + 16
MAX_SEGMENT_SIZE = 4 * 1024
TERMINATION_HEADER = (b'\x00' * 18)
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):
try:
data = await self.reader.readexactly(HEADER_LENGTH)
except IncompleteReadError:
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.readexactly(length)
body = box.decrypt(mac + data, inc_nonce(self.nonce))
self.nonce = inc_nonce(inc_nonce(self.nonce))
return body
@async_generator
async def __aiter__(self):
while True:
data = await self.read()
if data is None:
return
await 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):
for chunk in split_chunks(data, MAX_SEGMENT_SIZE):
body = self.box.encrypt(chunk, 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:])
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