#!/usr/bin/python
#
# This is a python script. You need a Python interpreter to run it.
# For example, ActiveState Python, which exists for windows.
#
# It can run standalone to convert files, or it can be installed as a
# plugin for Calibre (http://calibre-ebook.com/about) so that
# importing files with DRM 'Just Works'.
#
# To create a Calibre plugin, rename this file so that the filename
# ends in '_plugin.py', put it into a ZIP file and import that Calibre
# using its plugin configuration GUI.
#
# Changelog
#  0.01 - Initial version
#  0.02 - Huffdic compressed books were not properly decrypted
#  0.03 - Wasn't checking MOBI header length
#  0.04 - Wasn't sanity checking size of data record
#  0.05 - It seems that the extra data flags take two bytes not four
#  0.06 - And that low bit does mean something after all :-)
#  0.07 - The extra data flags aren't present in MOBI header < 0xE8

import sys,struct,binascii

class DrmException(Exception):
    pass

#implementation of Pukall Cipher 1
def PC1(key, src, decryption=True):
    sum1 = 0;
    sum2 = 0;
    keyXorVal = 0;
    if len(key)!=16:
        print "Bad key length!"
        return None
    wkey = []
    for i in xrange(8):
        wkey.append(ord(key[i*2])<<8 | ord(key[i*2+1]))

    dst = ""
    for i in xrange(len(src)):
        temp1 = 0;
        byteXorVal = 0;
        for j in xrange(8):
            temp1 ^= wkey[j]
            sum2  = (sum2+j)*20021 + sum1
            sum1  = (temp1*346)&0xFFFF
            sum2  = (sum2+sum1)&0xFFFF
            temp1 = (temp1*20021+1)&0xFFFF
            byteXorVal ^= temp1 ^ sum2
        curByte = ord(src[i])
        if not decryption:
            keyXorVal = curByte * 257;
        curByte = ((curByte ^ (byteXorVal >> 8)) ^ byteXorVal) & 0xFF
        if decryption:
            keyXorVal = curByte * 257;
        for j in xrange(8):
            wkey[j] ^= keyXorVal;
        dst+=chr(curByte)
    return dst

def checksumPid(s):
    letters = "ABCDEFGHIJKLMNPQRSTUVWXYZ123456789"
    crc = (~binascii.crc32(s,-1))&0xFFFFFFFF
    crc = crc ^ (crc >> 16)
    res = s
    l = len(letters)
    for i in (0,1):
        b = crc & 0xff
        pos = (b // l) ^ (b % l)
        res += letters[pos%l]
        crc >>= 8
    return res

def getSizeOfTrailingDataEntries(ptr, size, flags):
    def getSizeOfTrailingDataEntry(ptr, size):
        bitpos, result = 0, 0
        if size <= 0:
            return result
        while True:
            v = ord(ptr[size-1])
            result |= (v & 0x7F) << bitpos
            bitpos += 7
            size -= 1
            if (v & 0x80) != 0 or (bitpos >= 28) or (size == 0):
                return result
    num = 0
    testflags = flags >> 1
    while testflags:
        if testflags & 1:
            num += getSizeOfTrailingDataEntry(ptr, size - num)
        testflags >>= 1
    if flags & 1:
        num += (ord(ptr[size - num - 1]) & 0x3) + 1
    return num

class DrmStripper:
    def loadSection(self, section):
        if (section + 1 == self.num_sections):
            endoff = len(self.data_file)
        else:
            endoff = self.sections[section + 1][0]
        off = self.sections[section][0]
        return self.data_file[off:endoff]

    def patch(self, off, new):
        self.data_file = self.data_file[:off] + new + self.data_file[off+len(new):]

    def patchSection(self, section, new, in_off = 0):
        if (section + 1 == self.num_sections):
            endoff = len(self.data_file)
        else:
            endoff = self.sections[section + 1][0]
        off = self.sections[section][0]
        assert off + in_off + len(new) <= endoff
        self.patch(off + in_off, new)

    def parseDRM(self, data, count, pid):
        pid = pid.ljust(16,'\0')
        keyvec1 = "\x72\x38\x33\xB0\xB4\xF2\xE3\xCA\xDF\x09\x01\xD6\xE2\xE0\x3F\x96"
        temp_key = PC1(keyvec1, pid, False)
        temp_key_sum = sum(map(ord,temp_key)) & 0xff
        found_key = None
        for i in xrange(count):
            verification, size, type, cksum, cookie = struct.unpack('>LLLBxxx32s', data[i*0x30:i*0x30+0x30])
            cookie = PC1(temp_key, cookie)
            ver,flags,finalkey,expiry,expiry2 = struct.unpack('>LL16sLL', cookie)
            if verification == ver and cksum == temp_key_sum and (flags & 0x1F) == 1:
                found_key = finalkey
                break
        return found_key


    def __init__(self, data_file, pid):

        if checksumPid(pid[0:-2]) != pid:
            raise DrmException("invalid PID checksum")
        pid = pid[0:-2]

        self.data_file = data_file
        header = data_file[0:72]
        if header[0x3C:0x3C+8] != 'BOOKMOBI':
            raise DrmException("invalid file format")
        self.num_sections, = struct.unpack('>H', data_file[76:78])

        self.sections = []
        for i in xrange(self.num_sections):
            offset, a1,a2,a3,a4 = struct.unpack('>LBBBB', data_file[78+i*8:78+i*8+8])
            flags, val = a1, a2<<16|a3<<8|a4
            self.sections.append( (offset, flags, val) )

        sect = self.loadSection(0)
        records, = struct.unpack('>H', sect[0x8:0x8+2])
        mobi_length, = struct.unpack('>L',sect[0x14:0x18])
        extra_data_flags = 0
        if mobi_length >= 0xE8:
            extra_data_flags, = struct.unpack('>H', sect[0xF2:0xF4])


        crypto_type, = struct.unpack('>H', sect[0xC:0xC+2])
        if crypto_type == 0:
            raise DrmException("it seems that this book isn't encrypted")
        if crypto_type == 1:
            raise DrmException("cannot decode Mobipocket encryption type 1")
        if crypto_type != 2:
            raise DrmException("unknown encryption type: %d" % crypto_type)

        # calculate the keys
        drm_ptr, drm_count, drm_size, drm_flags = struct.unpack('>LLLL', sect[0xA8:0xA8+16])
        if drm_count == 0:
            raise DrmException("no PIDs found in this file")
        found_key = self.parseDRM(sect[drm_ptr:drm_ptr+drm_size], drm_count, pid)
        if not found_key:
            raise DrmException("no key found. maybe the PID is incorrect")

        # kill the drm keys
        self.patchSection(0, "\0" * drm_size, drm_ptr)
        # kill the drm pointers
        self.patchSection(0, "\xff" * 4 + "\0" * 12, 0xA8)
        # clear the crypto type
        self.patchSection(0, "\0" * 2, 0xC)

        # decrypt sections
        print "Decrypting. Please wait...",
        for i in xrange(1, records+1):
            data = self.loadSection(i)
            extra_size = getSizeOfTrailingDataEntries(data, len(data), extra_data_flags)
            self.patchSection(i, PC1(found_key, data[0:len(data) - extra_size]))
        print "done"
    def getResult(self):
        return self.data_file

if not __name__ == "__main__":
    from calibre.customize import FileTypePlugin

    class MobiDeDRM(FileTypePlugin):

        name                = 'MobiDeDRM' # Name of the plugin
        description         = 'Removes DRM from secure Mobi files'
        supported_platforms = ['linux', 'osx', 'windows'] # Platforms this plugin will run on
        author              = 'The Dark Reverser' # The author of this plugin
        version             = (0, 0, 7)   # The version number of this plugin
        file_types          = set(['prc','mobi','awz']) # The file types that this plugin will be applied to
        on_import           = True # Run this plugin during the import


        def run(self, path_to_ebook):
            of = self.temporary_file('.mobi')
            PID = self.site_customization
            data_file = file(path_to_ebook, 'rb').read()
            ar = PID.split(',')
            for i in ar:
                try:
                    file(of.name, 'wb').write(DrmStripper(data_file, i).getResult())
                except DrmException:
                    # Hm, we should display an error dialog here.
                    # Dunno how though.
                    # Ignore the dirty hack behind the curtain.
#                   strexcept = 'echo exception: %s > /dev/tty' % e
#                   subprocess.call(strexcept,shell=True)
                    print i + ": not PID for book"
                else:
                    return of.name

        def customization_help(self, gui=False):
            return 'Enter PID (separate multiple PIDs with comma)'

if __name__ == "__main__":
    print "MobiDeDrm v0.07. Copyright (c) 2008 The Dark Reverser"
    if len(sys.argv)<4:
        print "Removes protection from Mobipocket books"
        print "Usage:"
        print "  mobidedrm infile.mobi outfile.mobi PID"
    else:
        infile = sys.argv[1]
        outfile = sys.argv[2]
        pid = sys.argv[3]
        data_file = file(infile, 'rb').read()
        try:
            file(outfile, 'wb').write(DrmStripper(data_file, pid).getResult())
        except DrmException, e:
            print "Error: %s" % e