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