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# -*- coding: utf-8 -*-
#
# pyhwp : hwp file format parser in python
# Copyright (C) 2010-2023 mete0r <https://github.com/mete0r>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
#
''' Decode distribute docs.
Based on the algorithm described by Changwoo Ryu
See https://groups.google.com/forum/#!topic/hwp-foss/d2KL2ypR89Q
'''
from __future__ import absolute_import
from __future__ import print_function
from __future__ import unicode_literals
from io import BytesIO
import logging
from .plat import get_aes128ecb_decrypt
from .recordstream import read_record
from .tagids import HWPTAG_DISTRIBUTE_DOC_DATA
logger = logging.getLogger(__name__)
def decode(stream):
distdoc_data_record = read_record(stream, 0)
if distdoc_data_record['tagid'] != HWPTAG_DISTRIBUTE_DOC_DATA:
raise IOError('the first record is not an HWPTAG_DISTRIBUTE_DOC_DATA')
distdoc_data = distdoc_data_record['payload']
key = decode_head_to_key(distdoc_data)
tail = stream.read()
decrypted = decrypt_tail(key, tail)
return BytesIO(decrypted)
class Random:
''' MSVC's srand()/rand() like pseudorandom generator.
'''
def __init__(self, seed):
self.seed = seed
def rand(self):
self.seed = (self.seed * 214013 + 2531011) & 0xffffffff
value = (self.seed >> 16) & 0x7fff
return value
def decode_head_to_sha1(record_payload):
''' Decode HWPTAG_DISTRIBUTE_DOC_DATA.
It's the sha1 digest of user-supplied password string, i.e.,
'12345' -> hashlib.sha1('12345').digest()
'''
if len(record_payload) != 256:
raise ValueError('payload size must be 256 bytes')
data = bytearray(record_payload)
seed = data[3] << 24 | data[2] << 16 | data[1] << 8 | data[0]
random = Random(seed)
n = 0
for i in range(256):
if n == 0:
key = random.rand() & 0xff
n = (random.rand() & 0xf) + 1
if i >= 4:
data[i] = data[i] ^ key
n -= 1
# decoded = b''.join(chr(x) for x in data)
decoded = data
sha1offset = 4 + (seed & 0xf)
ucs16le = decoded[sha1offset:sha1offset + 80]
return ucs16le
def decode_head_to_key(record_payload):
sha1ucs16le = decode_head_to_sha1(record_payload)
return sha1ucs16le[:16]
def decrypt_tail(key, encrypted_tail):
decrypt = get_aes128ecb_decrypt()
return decrypt(key, encrypted_tail)
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