pyssb/ssb/boxstream.py

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2017-05-25 10:47:01 +00:00
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' * HEADER_LENGTH)
MAX_NONCE = (8 * NONCE_SIZE)
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):
shared_secret = kwargs.pop('shared_secret')
return UnboxStream(reader, shared_secret, **kwargs), BoxStream(writer, shared_secret, **kwargs)
class UnboxStream(object):
def __init__(self, reader, shared_secret, **key_data):
self.reader = reader
self.decrypt_key = key_data.get('decrypt_key')
self.decrypt_nonce = key_data.get('decrypt_nonce')
async def process(self):
while True:
data = await self.reader.read(HEADER_LENGTH)
if not data:
break
box = SecretBox(self.decrypt_key)
header = box.decrypt(data, self.decrypt_nonce)
if header == TERMINATION_HEADER:
return
length = struct.unpack('>H', header[:2])[0]
mac = header[2:]
data = await self.reader.read(length)
self.decrypt_nonce = inc_nonce(self.decrypt_nonce)
body = box.decrypt(mac + data, self.decrypt_nonce)
self.decrypt_nonce = inc_nonce(self.decrypt_nonce)
yield body
print('Disconnect')
class BoxStream(object):
def __init__(self, writer, shared_secret, **key_data):
self.writer = writer
self.encrypt_key = key_data.get('decrypt_key')
self.encrypt_nonce = key_data.get('decrypt_nonce')
async def write(self, data):
box = SecretBox(self.encrypt_key)
# XXX: This nonce logic is almost for sure wrong
self.encrypt_nonce = inc_nonce(self.encrypt_nonce)
body = box.encrypt(data, self.encrypt_nonce)
header = struct.pack('>H', len(body)) + body[:16]
self.writer.write(box.encrypt(header, self.encrypt_nonce))
self.encrypt_nonce = inc_nonce(self.encrypt_nonce)
self.writer.write(body)