DeDRM_tools/DeDRM_plugin/epubfontdecrypt.py

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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# epubfontdecrypt.py
# Copyright © 2021 by noDRM
# Released under the terms of the GNU General Public Licence, version 3
# <http://www.gnu.org/licenses/>
# Revision history:
# 1 - Initial release
"""
Decrypts / deobfuscates font files in EPUB files
"""
__license__ = 'GPL v3'
__version__ = "1"
import os
import traceback
import zlib
import zipfile
from zipfile import ZipInfo, ZipFile, ZIP_STORED, ZIP_DEFLATED
from contextlib import closing
import xml.etree.ElementTree as etree
import itertools
import hashlib
import binascii
class Decryptor(object):
def __init__(self, obfuscationkeyIETF, obfuscationkeyAdobe, encryption):
enc = lambda tag: '{%s}%s' % ('http://www.w3.org/2001/04/xmlenc#', tag)
dsig = lambda tag: '{%s}%s' % ('http://www.w3.org/2000/09/xmldsig#', tag)
self.obfuscation_key_Adobe = obfuscationkeyAdobe
self.obfuscation_key_IETF = obfuscationkeyIETF
self._encryption = etree.fromstring(encryption)
# This loops through all entries in the "encryption.xml" file
# to figure out which files need to be decrypted.
self._obfuscatedIETF = obfuscatedIETF = set()
self._obfuscatedAdobe = obfuscatedAdobe = set()
self._other = other = set()
self._json_elements_to_remove = json_elements_to_remove = set()
self._has_remaining_xml = False
expr = './%s/%s/%s' % (enc('EncryptedData'), enc('CipherData'),
enc('CipherReference'))
for elem in self._encryption.findall(expr):
path = elem.get('URI', None)
encryption_type_url = (elem.getparent().getparent().find("./%s" % (enc('EncryptionMethod'))).get('Algorithm', None))
if path is not None:
if encryption_type_url == "http://www.idpf.org/2008/embedding":
# Font files obfuscated with the IETF algorithm
path = path.encode('utf-8')
obfuscatedIETF.add(path)
if (self.obfuscation_key_IETF is None):
self._has_remaining_xml = True
else:
json_elements_to_remove.add(elem.getparent().getparent())
elif encryption_type_url == "http://ns.adobe.com/pdf/enc#RC":
# Font files obfuscated with the Adobe algorithm.
path = path.encode('utf-8')
obfuscatedAdobe.add(path)
if (self.obfuscation_key_Adobe is None):
self._has_remaining_xml = True
else:
json_elements_to_remove.add(elem.getparent().getparent())
else:
path = path.encode('utf-8')
other.add(path)
self._has_remaining_xml = True
# Other unsupported type.
for elem in json_elements_to_remove:
elem.getparent().remove(elem)
def check_if_remaining(self):
return self._has_remaining_xml
def get_xml(self):
return "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" + etree.tostring(self._encryption, encoding="utf-8", pretty_print=True, xml_declaration=False).decode("utf-8")
def decompress(self, bytes):
dc = zlib.decompressobj(-15)
try:
decompressed_bytes = dc.decompress(bytes)
ex = dc.decompress(b'Z') + dc.flush()
if ex:
decompressed_bytes = decompressed_bytes + ex
except:
# possibly not compressed by zip - just return bytes
return bytes, False
return decompressed_bytes , True
def decrypt(self, path, data):
if path.encode('utf-8') in self._obfuscatedIETF and self.obfuscation_key_IETF is not None:
# de-obfuscate according to the IETF standard
data, was_decomp = self.decompress(data)
if len(data) <= 1040:
# de-obfuscate whole file
out = self.deobfuscate_single_data(self.obfuscation_key_IETF, data)
else:
out = self.deobfuscate_single_data(self.obfuscation_key_IETF, data[:1040]) + data[1040:]
if (not was_decomp):
out, was_decomp = self.decompress(out)
return out
elif path.encode('utf-8') in self._obfuscatedAdobe and self.obfuscation_key_Adobe is not None:
# de-obfuscate according to the Adobe standard
data, was_decomp = self.decompress(data)
if len(data) <= 1024:
# de-obfuscate whole file
out = self.deobfuscate_single_data(self.obfuscation_key_Adobe, data)
else:
out = self.deobfuscate_single_data(self.obfuscation_key_Adobe, data[:1024]) + data[1024:]
if (not was_decomp):
out, was_decomp = self.decompress(out)
return out
else:
# Not encrypted or obfuscated
return data
def deobfuscate_single_data(self, key, data):
msg = bytes([c^k for c,k in zip(data, itertools.cycle(key))])
return msg
def decryptFontsBook(inpath, outpath):
with closing(ZipFile(open(inpath, 'rb'))) as inf:
namelist = set(inf.namelist())
if 'META-INF/encryption.xml' not in namelist:
print("{0:s} has no obfuscated fonts".format(os.path.basename(inpath)))
return 1
# Font key handling:
font_master_key = None
adobe_master_encryption_key = None
contNS = lambda tag: '{%s}%s' % ('urn:oasis:names:tc:opendocument:xmlns:container', tag)
path = None
try:
container = etree.fromstring(inf.read("META-INF/container.xml"))
rootfiles = container.find(contNS("rootfiles")).findall(contNS("rootfile"))
for rootfile in rootfiles:
path = rootfile.get("full-path", None)
if (path is not None):
break
except:
pass
# If path is None, we didn't find an OPF, so we probably don't have a font key.
# If path is set, it's the path to the main content OPF file.
if (path is None):
print("No OPF for font obfuscation found")
return 1
else:
packageNS = lambda tag: '{%s}%s' % ('http://www.idpf.org/2007/opf', tag)
metadataDCNS = lambda tag: '{%s}%s' % ('http://purl.org/dc/elements/1.1/', tag)
try:
container = etree.fromstring(inf.read(path))
except:
container = []
## IETF font key algorithm:
print("Checking {0} for IETF font obfuscation keys ... ".format(path), end='')
secret_key_name = None
try:
secret_key_name = container.get("unique-identifier")
except:
pass
try:
identify_element = container.find(packageNS("metadata")).find(metadataDCNS("identifier"))
if (secret_key_name is None or secret_key_name == identify_element.get("id")):
font_master_key = identify_element.text
except:
pass
if (font_master_key is not None):
if (secret_key_name is None):
print("found '%s'" % (font_master_key))
else:
print("found '%s' (%s)" % (font_master_key, secret_key_name))
# Trim / remove forbidden characters from the key, then hash it:
font_master_key = font_master_key.replace(' ', '')
font_master_key = font_master_key.replace('\t', '')
font_master_key = font_master_key.replace('\r', '')
font_master_key = font_master_key.replace('\n', '')
font_master_key = font_master_key.encode('utf-8')
font_master_key = hashlib.sha1(font_master_key).digest()
else:
print("not found")
## Adobe font key algorithm
print("Checking {0} for Adobe font obfuscation keys ... ".format(path), end='')
try:
metadata = container.find(packageNS("metadata"))
identifiers = metadata.findall(metadataDCNS("identifier"))
uid = None
uidMalformed = False
for identifier in identifiers:
if identifier.get(packageNS("scheme")) == "UUID":
if identifier.text[:9] == "urn:uuid:":
uid = identifier.text[9:]
else:
uid = identifier.text
break
if identifier.text[:9] == "urn:uuid:":
uid = identifier.text[9:]
break
if uid is not None:
uid = uid.replace(chr(0x20),'').replace(chr(0x09),'')
uid = uid.replace(chr(0x0D),'').replace(chr(0x0A),'').replace('-','')
if len(uid) < 16:
uidMalformed = True
if not all(c in "0123456789abcdefABCDEF" for c in uid):
uidMalformed = True
if not uidMalformed:
print("found '{0}'".format(uid))
uid = uid + uid
adobe_master_encryption_key = binascii.unhexlify(uid[:32])
if adobe_master_encryption_key is None:
print("not found")
except:
print("exception")
pass
# Begin decrypting.
try:
encryption = inf.read('META-INF/encryption.xml')
decryptor = Decryptor(font_master_key, adobe_master_encryption_key, encryption)
kwds = dict(compression=ZIP_DEFLATED, allowZip64=False)
with closing(ZipFile(open(outpath, 'wb'), 'w', **kwds)) as outf:
# Mimetype needs to be the first entry, so remove it from the list
# whereever it is, then add it at the beginning.
namelist.remove("mimetype")
for path in (["mimetype"] + namelist):
data = inf.read(path)
zi = ZipInfo(path)
zi.compress_type=ZIP_DEFLATED
if path == "mimetype":
# mimetype must not be compressed
zi.compress_type = ZIP_STORED
elif path == "META-INF/encryption.xml":
# Check if there's still other entries not related to fonts
if (decryptor.check_if_remaining()):
data = decryptor.get_xml()
print("There's remaining entries in encryption.xml, adding file ...")
else:
# No remaining entries, no need for that file.
continue
try:
# get the file info, including time-stamp
oldzi = inf.getinfo(path)
# copy across useful fields
zi.date_time = oldzi.date_time
zi.comment = oldzi.comment
zi.extra = oldzi.extra
zi.internal_attr = oldzi.internal_attr
# external attributes are dependent on the create system, so copy both.
zi.external_attr = oldzi.external_attr
zi.create_system = oldzi.create_system
if any(ord(c) >= 128 for c in path) or any(ord(c) >= 128 for c in zi.comment):
# If the file name or the comment contains any non-ASCII char, set the UTF8-flag
zi.flag_bits |= 0x800
except:
pass
if path == "mimetype":
outf.writestr(zi, inf.read('mimetype'))
elif path == "META-INF/encryption.xml":
outf.writestr(zi, data)
else:
outf.writestr(zi, decryptor.decrypt(path, data))
except:
print("Could not decrypt fonts in {0:s} because of an exception:\n{1:s}".format(os.path.basename(inpath), traceback.format_exc()))
return 2
return 0