/usr/lib/python2.7/dist-packages/pdfrw/crypt.py is in python-pdfrw 0.4-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 | # A part of pdfrw (https://github.com/pmaupin/pdfrw)
# Copyright (C) 2017 Jon Lund Steffensen
# MIT license -- See LICENSE.txt for details
from __future__ import division
import hashlib
import struct
try:
from Crypto.Cipher import ARC4, AES
HAS_CRYPTO = True
except ImportError:
HAS_CRYPTO = False
from .objects import PdfDict, PdfName
_PASSWORD_PAD = (
'(\xbfN^Nu\x8aAd\x00NV\xff\xfa\x01\x08'
'..\x00\xb6\xd0h>\x80/\x0c\xa9\xfedSiz')
def streamobjects(mylist, isinstance=isinstance, PdfDict=PdfDict):
for obj in mylist:
if isinstance(obj, PdfDict) and obj.stream is not None:
yield obj
def create_key(password, doc):
"""Create an encryption key (Algorithm 2 in PDF spec)."""
key_size = int(doc.Encrypt.Length or 40) // 8
padded_pass = (password + _PASSWORD_PAD)[:32]
hasher = hashlib.md5()
hasher.update(padded_pass)
hasher.update(doc.Encrypt.O.to_bytes())
hasher.update(struct.pack('<i', int(doc.Encrypt.P)))
hasher.update(doc.ID[0].to_bytes())
temp_hash = hasher.digest()
if int(doc.Encrypt.R or 0) >= 3:
for _ in range(50):
temp_hash = hashlib.md5(temp_hash[:key_size]).digest()
return temp_hash[:key_size]
def create_user_hash(key, doc):
"""Create the user password hash (Algorithm 4/5)."""
revision = int(doc.Encrypt.R or 0)
if revision < 3:
cipher = ARC4.new(key)
return cipher.encrypt(_PASSWORD_PAD)
else:
hasher = hashlib.md5()
hasher.update(_PASSWORD_PAD)
hasher.update(doc.ID[0].to_bytes())
temp_hash = hasher.digest()
for i in range(20):
temp_key = ''.join(chr(i ^ ord(x)) for x in key)
cipher = ARC4.new(temp_key)
temp_hash = cipher.encrypt(temp_hash)
return temp_hash
def check_user_password(key, doc):
"""Check that the user password is correct (Algorithm 6)."""
expect_user_hash = create_user_hash(key, doc)
revision = int(doc.Encrypt.R or 0)
if revision < 3:
return doc.Encrypt.U.to_bytes() == expect_user_hash
else:
return doc.Encrypt.U.to_bytes()[:16] == expect_user_hash
class AESCryptFilter(object):
"""Crypt filter corresponding to /AESV2."""
def __init__(self, key):
self._key = key
def decrypt_data(self, num, gen, data):
"""Decrypt data (string/stream) using key (Algorithm 1)."""
key_extension = struct.pack('<i', num)[:3]
key_extension += struct.pack('<i', gen)[:2]
key_extension += 'sAlT'
temp_key = self._key + key_extension
temp_key = hashlib.md5(temp_key).digest()
iv = data[:AES.block_size]
cipher = AES.new(temp_key, AES.MODE_CBC, iv)
decrypted = cipher.decrypt(data[AES.block_size:])
# Remove padding
pad_size = ord(decrypted[-1])
assert 1 <= pad_size <= 16
return decrypted[:-pad_size]
class RC4CryptFilter(object):
"""Crypt filter corresponding to /V2."""
def __init__(self, key):
self._key = key
def decrypt_data(self, num, gen, data):
"""Decrypt data (string/stream) using key (Algorithm 1)."""
new_key_size = min(len(self._key) + 5, 16)
key_extension = struct.pack('<i', num)[:3]
key_extension += struct.pack('<i', gen)[:2]
temp_key = self._key + key_extension
temp_key = hashlib.md5(temp_key).digest()[:new_key_size]
cipher = ARC4.new(temp_key)
return cipher.decrypt(data)
class IdentityCryptFilter(object):
"""Identity crypt filter (pass through with no encryption)."""
def decrypt_data(self, num, gen, data):
return data
def decrypt_objects(objects, default_filter, filters):
"""Decrypt list of stream objects.
The parameter default_filter specifies the default filter to use. The
filters parameter is a dictionary of alternate filters to use when the
object specfies an alternate filter locally.
"""
for obj in streamobjects(objects):
if getattr(obj, 'decrypted', False):
continue
filter = default_filter
# Check whether a locally defined crypt filter should override the
# default filter.
ftype = obj.Filter
if ftype is not None:
if not isinstance(ftype, list):
ftype = [ftype]
if len(ftype) >= 1 and ftype[0] == PdfName.Crypt:
ftype = ftype[1:]
parms = obj.DecodeParms or obj.DP
filter = filters[parms.Name]
num, gen = obj.indirect
obj.stream = filter.decrypt_data(num, gen, obj.stream)
obj.private.decrypted = True
obj.Filter = ftype or None
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