shadowsocksr/shadowsocks/obfsplugin/obfs_tls.py

#!/usr/bin/env python
#
# Copyright 2015-2015 breakwa11
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.

from __future__ import absolute_import, division, print_function, \
    with_statement

import os
import sys
import hashlib
import logging
import binascii
import struct
import base64
import time
import random
import hmac
import hashlib
import string

from shadowsocks import common
from shadowsocks.obfsplugin import plain
from shadowsocks.common import to_bytes, to_str, ord
from shadowsocks import lru_cache

def create_tls_ticket_auth_obfs(method):
    return tls_ticket_auth(method)

obfs_map = {
        'tls1.2_ticket_auth': (create_tls_ticket_auth_obfs,),
        'tls1.2_ticket_auth_compatible': (create_tls_ticket_auth_obfs,),
}

def match_begin(str1, str2):
    if len(str1) >= len(str2):
        if str1[:len(str2)] == str2:
            return True
    return False

class obfs_auth_data(object):
    def __init__(self):
        self.client_data = lru_cache.LRUCache(60 * 5)
        self.client_id = os.urandom(32)
        self.startup_time = int(time.time() - 60 * 30) & 0xFFFFFFFF
        self.ticket_buf = {}

class tls_ticket_auth(plain.plain):
    def __init__(self, method):
        self.method = method
        self.handshake_status = 0
        self.send_buffer = b''
        self.recv_buffer = b''
        self.client_id = b''
        self.max_time_dif = 60 * 60 * 24 # time dif (second) setting
        self.tls_version = b'\x03\x03'
        self.overhead = 5

    def init_data(self):
        return obfs_auth_data()

    def get_overhead(self, direction): # direction: true for c->s false for s->c
        return self.overhead

    def sni(self, url):
        url = common.to_bytes(url)
        data = b"\x00" + struct.pack('>H', len(url)) + url
        data = b"\x00\x00" + struct.pack('>H', len(data) + 2) + struct.pack('>H', len(data)) + data
        return data

    def pack_auth_data(self, client_id):
        utc_time = int(time.time()) & 0xFFFFFFFF
        data = struct.pack('>I', utc_time) + os.urandom(18)
        data += hmac.new(self.server_info.key + client_id, data, hashlib.sha1).digest()[:10]
        return data

    def client_encode(self, buf):
        if self.handshake_status == -1:
            return buf
        if self.handshake_status == 8:
            ret = b''
            while len(buf) > 2048:
                size = min(struct.unpack('>H', os.urandom(2))[0] % 4096 + 100, len(buf))
                ret += b"\x17" + self.tls_version + struct.pack('>H', size) + buf[:size]
                buf = buf[size:]
            if len(buf) > 0:
                ret += b"\x17" + self.tls_version + struct.pack('>H', len(buf)) + buf
            return ret
        if len(buf) > 0:
            self.send_buffer += b"\x17" + self.tls_version + struct.pack('>H', len(buf)) + buf
        if self.handshake_status == 0:
            self.handshake_status = 1
            data = self.tls_version + self.pack_auth_data(self.server_info.data.client_id) + b"\x20" + self.server_info.data.client_id + binascii.unhexlify(b"001cc02bc02fcca9cca8cc14cc13c00ac014c009c013009c0035002f000a" + b"0100")
            ext = binascii.unhexlify(b"ff01000100")
            host = self.server_info.obfs_param or self.server_info.host
            if host and host[-1] in string.digits:
                host = ''
            hosts = host.split(',')
            host = random.choice(hosts)
            ext += self.sni(host)
            ext += b"\x00\x17\x00\x00"
            if host not in self.server_info.data.ticket_buf:
                self.server_info.data.ticket_buf[host] = os.urandom((struct.unpack('>H', os.urandom(2))[0] % 17 + 8) * 16)
            ext += b"\x00\x23" + struct.pack('>H', len(self.server_info.data.ticket_buf[host])) + self.server_info.data.ticket_buf[host]
            ext += binascii.unhexlify(b"000d001600140601060305010503040104030301030302010203")
            ext += binascii.unhexlify(b"000500050100000000")
            ext += binascii.unhexlify(b"00120000")
            ext += binascii.unhexlify(b"75500000")
            ext += binascii.unhexlify(b"000b00020100")
            ext += binascii.unhexlify(b"000a0006000400170018")
            data += struct.pack('>H', len(ext)) + ext
            data = b"\x01\x00" + struct.pack('>H', len(data)) + data
            data = b"\x16\x03\x01" + struct.pack('>H', len(data)) + data
            return data
        elif self.handshake_status == 1 and len(buf) == 0:
            data = b"\x14" + self.tls_version + b"\x00\x01\x01" #ChangeCipherSpec
            data += b"\x16" + self.tls_version + b"\x00\x20" + os.urandom(22) #Finished
            data += hmac.new(self.server_info.key + self.server_info.data.client_id, data, hashlib.sha1).digest()[:10]
            ret = data + self.send_buffer
            self.send_buffer = b''
            self.handshake_status = 8
            return ret
        return b''

    def client_decode(self, buf):
        if self.handshake_status == -1:
            return (buf, False)

        if self.handshake_status == 8:
            ret = b''
            self.recv_buffer += buf
            while len(self.recv_buffer) > 5:
                if ord(self.recv_buffer[0]) != 0x17:
                    logging.info("data = %s" % (binascii.hexlify(self.recv_buffer)))
                    raise Exception('server_decode appdata error')
                size = struct.unpack('>H', self.recv_buffer[3:5])[0]
                if len(self.recv_buffer) < size + 5:
                    break
                buf = self.recv_buffer[5:size+5]
                ret += buf
                self.recv_buffer = self.recv_buffer[size+5:]
            return (ret, False)

        if len(buf) < 11 + 32 + 1 + 32:
            raise Exception('client_decode data error')
        verify = buf[11:33]
        if hmac.new(self.server_info.key + self.server_info.data.client_id, verify, hashlib.sha1).digest()[:10] != buf[33:43]:
            raise Exception('client_decode data error')
        if hmac.new(self.server_info.key + self.server_info.data.client_id, buf[:-10], hashlib.sha1).digest()[:10] != buf[-10:]:
            raise Exception('client_decode data error')
        return (b'', True)

    def server_encode(self, buf):
        if self.handshake_status == -1:
            return buf
        if (self.handshake_status & 8) == 8:
            ret = b''
            while len(buf) > 2048:
                size = min(struct.unpack('>H', os.urandom(2))[0] % 4096 + 100, len(buf))
                ret += b"\x17" + self.tls_version + struct.pack('>H', size) + buf[:size]
                buf = buf[size:]
            if len(buf) > 0:
                ret += b"\x17" + self.tls_version + struct.pack('>H', len(buf)) + buf
            return ret
        self.handshake_status |= 8
        data = self.tls_version + self.pack_auth_data(self.client_id) + b"\x20" + self.client_id + binascii.unhexlify(b"c02f000005ff01000100")
        data = b"\x02\x00" + struct.pack('>H', len(data)) + data #server hello
        data = b"\x16" + self.tls_version + struct.pack('>H', len(data)) + data
        if random.randint(0, 8) < 1:
            ticket = os.urandom((struct.unpack('>H', os.urandom(2))[0] % 164) * 2 + 64)
            ticket = struct.pack('>H', len(ticket) + 4) + b"\x04\x00" + struct.pack('>H', len(ticket)) + ticket
            data += b"\x16" + self.tls_version + ticket #New session ticket
        data += b"\x14" + self.tls_version + b"\x00\x01\x01" #ChangeCipherSpec
        finish_len = random.choice([32, 40])
        data += b"\x16" + self.tls_version + struct.pack('>H', finish_len) + os.urandom(finish_len - 10) #Finished
        data += hmac.new(self.server_info.key + self.client_id, data, hashlib.sha1).digest()[:10]
        if buf:
            data += self.server_encode(buf)
        return data

    def decode_error_return(self, buf):
        self.handshake_status = -1
        self.overhead = 0
        if self.method == 'tls1.2_ticket_auth':
            return (b'E'*2048, False, False)
        return (buf, True, False)

    def server_decode(self, buf):
        if self.handshake_status == -1:
            return (buf, True, False)

        if (self.handshake_status & 4) == 4:
            ret = b''
            self.recv_buffer += buf
            while len(self.recv_buffer) > 5:
                if ord(self.recv_buffer[0]) != 0x17 or ord(self.recv_buffer[1]) != 0x3 or ord(self.recv_buffer[2]) != 0x3:
                    logging.info("data = %s" % (binascii.hexlify(self.recv_buffer)))
                    raise Exception('server_decode appdata error')
                size = struct.unpack('>H', self.recv_buffer[3:5])[0]
                if len(self.recv_buffer) < size + 5:
                    break
                ret += self.recv_buffer[5:size+5]
                self.recv_buffer = self.recv_buffer[size+5:]
            return (ret, True, False)

        if (self.handshake_status & 1) == 1:
            self.recv_buffer += buf
            buf = self.recv_buffer
            verify = buf
            if len(buf) < 11:
                raise Exception('server_decode data error')
            if not match_begin(buf, b"\x14" + self.tls_version + b"\x00\x01\x01"): #ChangeCipherSpec
                raise Exception('server_decode data error')
            buf = buf[6:]
            if not match_begin(buf, b"\x16" + self.tls_version + b"\x00"): #Finished
                raise Exception('server_decode data error')
            verify_len = struct.unpack('>H', buf[3:5])[0] + 1 # 11 - 10
            if len(verify) < verify_len + 10:
                return (b'', False, False)
            if hmac.new(self.server_info.key + self.client_id, verify[:verify_len], hashlib.sha1).digest()[:10] != verify[verify_len:verify_len+10]:
                raise Exception('server_decode data error')
            self.recv_buffer = verify[verify_len + 10:]
            status = self.handshake_status
            self.handshake_status |= 4
            ret = self.server_decode(b'')
            return ret;

        #raise Exception("handshake data = %s" % (binascii.hexlify(buf)))
        self.recv_buffer += buf
        buf = self.recv_buffer
        ogn_buf = buf
        if len(buf) < 3:
            return (b'', False, False)
        if not match_begin(buf, b'\x16\x03\x01'):
            return self.decode_error_return(ogn_buf)
        buf = buf[3:]
        header_len = struct.unpack('>H', buf[:2])[0]
        if header_len > len(buf) - 2:
            return (b'', False, False)

        self.recv_buffer = self.recv_buffer[header_len + 5:]
        self.handshake_status = 1
        buf = buf[2:header_len + 2]
        if not match_begin(buf, b'\x01\x00'): #client hello
            logging.info("tls_auth not client hello message")
            return self.decode_error_return(ogn_buf)
        buf = buf[2:]
        if struct.unpack('>H', buf[:2])[0] != len(buf) - 2:
            logging.info("tls_auth wrong message size")
            return self.decode_error_return(ogn_buf)
        buf = buf[2:]
        if not match_begin(buf, self.tls_version):
            logging.info("tls_auth wrong tls version")
            return self.decode_error_return(ogn_buf)
        buf = buf[2:]
        verifyid = buf[:32]
        buf = buf[32:]
        sessionid_len = ord(buf[0])
        if sessionid_len < 32:
            logging.info("tls_auth wrong sessionid_len")
            return self.decode_error_return(ogn_buf)
        sessionid = buf[1:sessionid_len + 1]
        buf = buf[sessionid_len+1:]
        self.client_id = sessionid
        sha1 = hmac.new(self.server_info.key + sessionid, verifyid[:22], hashlib.sha1).digest()[:10]
        utc_time = struct.unpack('>I', verifyid[:4])[0]
        time_dif = common.int32((int(time.time()) & 0xffffffff) - utc_time)
        if self.server_info.obfs_param:
            try:
                self.max_time_dif = int(self.server_info.obfs_param)
            except:
                pass
        if self.max_time_dif > 0 and (time_dif < -self.max_time_dif or time_dif > self.max_time_dif \
                or common.int32(utc_time - self.server_info.data.startup_time) < -self.max_time_dif / 2):
            logging.info("tls_auth wrong time")
            return self.decode_error_return(ogn_buf)
        if sha1 != verifyid[22:]:
            logging.info("tls_auth wrong sha1")
            return self.decode_error_return(ogn_buf)
        if self.server_info.data.client_data.get(verifyid[:22]):
            logging.info("replay attack detect, id = %s" % (binascii.hexlify(verifyid)))
            return self.decode_error_return(ogn_buf)
        self.server_info.data.client_data.sweep()
        self.server_info.data.client_data[verifyid[:22]] = sessionid
        if len(self.recv_buffer) >= 11:
            ret = self.server_decode(b'')
            return (ret[0], True, True)
        # (buffer_to_recv, is_need_decrypt, is_need_to_encode_and_send_back)
        return (b'', False, True)