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 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]) crypto_type, = struct.unpack('>H', sect[0xC:0xC+2]) if crypto_type != 2: raise DrmException("invalid encryption type: %d" % crypto_type) # calculate the keys drm_ptr, drm_count, drm_size, drm_flags = struct.unpack('>LLLL', sect[0xA8:0xA8+16]) 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): self.patchSection(i, PC1(found_key, self.loadSection(i))) print "done" def getResult(self): return self.data_file print "MobiDeDrm v0.01. Copyright (c) 2008 The Dark Reverser" if len(sys.argv)<4: print "Removes protection from Mobipocket books" print "Usage: 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