DeDRM_tools/DeDRM_plugin/ion.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

# ion.py
# Copyright © 2013-2020 Apprentice Harper et al.

__license__ = 'GPL v3'
__version__ = '3.0'

# Revision history:
#  Pascal implementation by lulzkabulz.
#  BinaryIon.pas + DrmIon.pas + IonSymbols.pas
#  1.0   - Python translation by apprenticenaomi.
#  1.1   - DeDRM integration by anon.
#  1.2   - Added pylzma import fallback
#  1.3   - Fixed lzma support for calibre 4.6+
#  2.0   - VoucherEnvelope v2/v3 support by apprenticesakuya.
#  3.0   - Added Python 3 compatibility for calibre 5.0

"""
Decrypt Kindle KFX files.
"""

import collections
import hashlib
import hmac
import os
import os.path
import struct

from io import BytesIO

from Crypto.Cipher import AES
from Crypto.Util.py3compat import bchr, bord

try:
    # lzma library from calibre 4.6.0 or later
    import calibre_lzma.lzma1 as calibre_lzma
except ImportError:
    calibre_lzma = None
    # lzma library from calibre 2.35.0 or later
    try:
        import lzma.lzma1 as calibre_lzma
    except ImportError:
        calibre_lzma = None
        try:
            import lzma
        except ImportError:
            # Need pip backports.lzma on Python <3.3
            try:
                from backports import lzma
            except ImportError:
                # Windows-friendly choice: pylzma wheels
                import pylzma as lzma


TID_NULL = 0
TID_BOOLEAN = 1
TID_POSINT = 2
TID_NEGINT = 3
TID_FLOAT = 4
TID_DECIMAL = 5
TID_TIMESTAMP = 6
TID_SYMBOL = 7
TID_STRING = 8
TID_CLOB = 9
TID_BLOB = 0xA
TID_LIST = 0xB
TID_SEXP = 0xC
TID_STRUCT = 0xD
TID_TYPEDECL = 0xE
TID_UNUSED = 0xF


SID_UNKNOWN = -1
SID_ION = 1
SID_ION_1_0 = 2
SID_ION_SYMBOL_TABLE = 3
SID_NAME = 4
SID_VERSION = 5
SID_IMPORTS = 6
SID_SYMBOLS = 7
SID_MAX_ID = 8
SID_ION_SHARED_SYMBOL_TABLE = 9
SID_ION_1_0_MAX = 10


LEN_IS_VAR_LEN = 0xE
LEN_IS_NULL = 0xF


VERSION_MARKER = b"\x01\x00\xEA"


# asserts must always raise exceptions for proper functioning
def _assert(test, msg="Exception"):
    if not test:
        raise Exception(msg)


class SystemSymbols(object):
    ION = '$ion'
    ION_1_0 = '$ion_1_0'
    ION_SYMBOL_TABLE = '$ion_symbol_table'
    NAME = 'name'
    VERSION = 'version'
    IMPORTS = 'imports'
    SYMBOLS = 'symbols'
    MAX_ID = 'max_id'
    ION_SHARED_SYMBOL_TABLE = '$ion_shared_symbol_table'


class IonCatalogItem(object):
    name = ""
    version = 0
    symnames = []

    def __init__(self, name, version, symnames):
        self.name = name
        self.version = version
        self.symnames = symnames


class SymbolToken(object):
    text = ""
    sid = 0

    def __init__(self, text, sid):
        if text == "" and sid == 0:
            raise ValueError("Symbol token must have Text or SID")

        self.text = text
        self.sid = sid


class SymbolTable(object):
    table = None

    def __init__(self):
        self.table = [None] * SID_ION_1_0_MAX
        self.table[SID_ION] = SystemSymbols.ION
        self.table[SID_ION_1_0] = SystemSymbols.ION_1_0
        self.table[SID_ION_SYMBOL_TABLE] = SystemSymbols.ION_SYMBOL_TABLE
        self.table[SID_NAME] = SystemSymbols.NAME
        self.table[SID_VERSION] = SystemSymbols.VERSION
        self.table[SID_IMPORTS] = SystemSymbols.IMPORTS
        self.table[SID_SYMBOLS] = SystemSymbols.SYMBOLS
        self.table[SID_MAX_ID] = SystemSymbols.MAX_ID
        self.table[SID_ION_SHARED_SYMBOL_TABLE] = SystemSymbols.ION_SHARED_SYMBOL_TABLE

    def findbyid(self, sid):
        if sid < 1:
            raise ValueError("Invalid symbol id")

        if sid < len(self.table):
            return self.table[sid]
        else:
            return ""

    def import_(self, table, maxid):
        for i in range(maxid):
            self.table.append(table.symnames[i])

    def importunknown(self, name, maxid):
        for i in range(maxid):
            self.table.append("%s#%d" % (name, i + 1))


class ParserState:
    Invalid,BeforeField,BeforeTID,BeforeValue,AfterValue,EOF = 1,2,3,4,5,6

ContainerRec = collections.namedtuple("ContainerRec", "nextpos, tid, remaining")


class BinaryIonParser(object):
    eof = False
    state = None
    localremaining = 0
    needhasnext = False
    isinstruct = False
    valuetid = 0
    valuefieldid = 0
    parenttid = 0
    valuelen = 0
    valueisnull = False
    valueistrue = False
    value = None
    didimports = False

    def __init__(self, stream):
        self.annotations = []
        self.catalog = []

        self.stream = stream
        self.initpos = stream.tell()
        self.reset()
        self.symbols = SymbolTable()

    def reset(self):
        self.state = ParserState.BeforeTID
        self.needhasnext = True
        self.localremaining = -1
        self.eof = False
        self.isinstruct = False
        self.containerstack = []
        self.stream.seek(self.initpos)

    def addtocatalog(self, name, version, symbols):
        self.catalog.append(IonCatalogItem(name, version, symbols))

    def hasnext(self):
        while self.needhasnext and not self.eof:
            self.hasnextraw()
            if len(self.containerstack) == 0 and not self.valueisnull:
                if self.valuetid == TID_SYMBOL:
                    if self.value == SID_ION_1_0:
                        self.needhasnext = True
                elif self.valuetid == TID_STRUCT:
                    for a in self.annotations:
                        if a == SID_ION_SYMBOL_TABLE:
                            self.parsesymboltable()
                            self.needhasnext = True
                            break
        return not self.eof

    def hasnextraw(self):
        self.clearvalue()
        while self.valuetid == -1 and not self.eof:
            self.needhasnext = False
            if self.state == ParserState.BeforeField:
                _assert(self.valuefieldid == SID_UNKNOWN)

                self.valuefieldid = self.readfieldid()
                if self.valuefieldid != SID_UNKNOWN:
                    self.state = ParserState.BeforeTID
                else:
                    self.eof = True

            elif self.state == ParserState.BeforeTID:
                self.state = ParserState.BeforeValue
                self.valuetid = self.readtypeid()
                if self.valuetid == -1:
                    self.state = ParserState.EOF
                    self.eof = True
                    break

                if self.valuetid == TID_TYPEDECL:
                    if self.valuelen == 0:
                        self.checkversionmarker()
                    else:
                        self.loadannotations()

            elif self.state == ParserState.BeforeValue:
                self.skip(self.valuelen)
                self.state = ParserState.AfterValue

            elif self.state == ParserState.AfterValue:
                if self.isinstruct:
                    self.state = ParserState.BeforeField
                else:
                    self.state = ParserState.BeforeTID

            else:
                _assert(self.state == ParserState.EOF)

    def next(self):
        if self.hasnext():
            self.needhasnext = True
            return self.valuetid
        else:
            return -1

    def push(self, typeid, nextposition, nextremaining):
        self.containerstack.append(ContainerRec(nextpos=nextposition, tid=typeid, remaining=nextremaining))

    def stepin(self):
        _assert(self.valuetid in [TID_STRUCT, TID_LIST, TID_SEXP] and not self.eof,
                "valuetid=%s eof=%s" % (self.valuetid, self.eof))
        _assert((not self.valueisnull or self.state == ParserState.AfterValue) and
               (self.valueisnull or self.state == ParserState.BeforeValue))

        nextrem = self.localremaining
        if nextrem != -1:
            nextrem -= self.valuelen
            if nextrem < 0:
                nextrem = 0
        self.push(self.parenttid, self.stream.tell() + self.valuelen, nextrem)

        self.isinstruct = (self.valuetid == TID_STRUCT)
        if self.isinstruct:
            self.state = ParserState.BeforeField
        else:
            self.state = ParserState.BeforeTID

        self.localremaining = self.valuelen
        self.parenttid = self.valuetid
        self.clearvalue()
        self.needhasnext = True

    def stepout(self):
        rec = self.containerstack.pop()

        self.eof = False
        self.parenttid = rec.tid
        if self.parenttid == TID_STRUCT:
            self.isinstruct = True
            self.state = ParserState.BeforeField
        else:
            self.isinstruct = False
            self.state = ParserState.BeforeTID
        self.needhasnext = True

        self.clearvalue()
        curpos = self.stream.tell()
        if rec.nextpos > curpos:
            self.skip(rec.nextpos - curpos)
        else:
            _assert(rec.nextpos == curpos)

        self.localremaining = rec.remaining

    def read(self, count=1):
        if self.localremaining != -1:
            self.localremaining -= count
            _assert(self.localremaining >= 0)

        result = self.stream.read(count)
        if len(result) == 0:
            raise EOFError()
        return result

    def readfieldid(self):
        if self.localremaining != -1 and self.localremaining < 1:
            return -1

        try:
            return self.readvaruint()
        except EOFError:
            return -1

    def readtypeid(self):
        if self.localremaining != -1:
            if self.localremaining < 1:
                return -1
            self.localremaining -= 1

        b = self.stream.read(1)
        if len(b) < 1:
            return -1
        b = bord(b)
        result = b >> 4
        ln = b & 0xF

        if ln == LEN_IS_VAR_LEN:
            ln = self.readvaruint()
        elif ln == LEN_IS_NULL:
            ln = 0
            self.state = ParserState.AfterValue
        elif result == TID_NULL:
            # Must have LEN_IS_NULL
            _assert(False)
        elif result == TID_BOOLEAN:
            _assert(ln <= 1)
            self.valueistrue = (ln == 1)
            ln = 0
            self.state = ParserState.AfterValue
        elif result == TID_STRUCT:
            if ln == 1:
                ln = self.readvaruint()

        self.valuelen = ln
        return result

    def readvarint(self):
        b = bord(self.read())
        negative = ((b & 0x40) != 0)
        result = (b & 0x3F)

        i = 0
        while (b & 0x80) == 0 and i < 4:
            b = bord(self.read())
            result = (result << 7) | (b & 0x7F)
            i += 1

        _assert(i < 4 or (b & 0x80) != 0, "int overflow")

        if negative:
            return -result
        return result

    def readvaruint(self):
        b = bord(self.read())
        result = (b & 0x7F)

        i = 0
        while (b & 0x80) == 0 and i < 4:
            b = bord(self.read())
            result = (result << 7) | (b & 0x7F)
            i += 1

        _assert(i < 4 or (b & 0x80) != 0, "int overflow")

        return result

    def readdecimal(self):
        if self.valuelen == 0:
            return 0.

        rem = self.localremaining - self.valuelen
        self.localremaining = self.valuelen
        exponent = self.readvarint()

        _assert(self.localremaining > 0, "Only exponent in ReadDecimal")
        _assert(self.localremaining <= 8, "Decimal overflow")

        signed = False
        b = [bord(x) for x in self.read(self.localremaining)]
        if (b[0] & 0x80) != 0:
            b[0] = b[0] & 0x7F
            signed = True

        # Convert variably sized network order integer into 64-bit little endian
        j = 0
        vb = [0] * 8
        for i in range(len(b), -1, -1):
            vb[i] = b[j]
            j += 1

        v = struct.unpack("<Q", b"".join(bchr(x) for x in vb))[0]

        result = v * (10 ** exponent)
        if signed:
            result = -result

        self.localremaining = rem
        return result

    def skip(self, count):
        if self.localremaining != -1:
            self.localremaining -= count
            if self.localremaining < 0:
                raise EOFError()

        self.stream.seek(count, os.SEEK_CUR)

    def parsesymboltable(self):
        self.next() # shouldn't do anything?

        _assert(self.valuetid == TID_STRUCT)

        if self.didimports:
            return

        self.stepin()

        fieldtype = self.next()
        while fieldtype != -1:
            if not self.valueisnull:
                _assert(self.valuefieldid == SID_IMPORTS, "Unsupported symbol table field id")

                if fieldtype == TID_LIST:
                    self.gatherimports()

            fieldtype = self.next()

        self.stepout()
        self.didimports = True

    def gatherimports(self):
        self.stepin()

        t = self.next()
        while t != -1:
            if not self.valueisnull and t == TID_STRUCT:
                self.readimport()

            t = self.next()

        self.stepout()

    def readimport(self):
        version = -1
        maxid = -1
        name = ""

        self.stepin()

        t = self.next()
        while t != -1:
            if not self.valueisnull and self.valuefieldid != SID_UNKNOWN:
                if self.valuefieldid == SID_NAME:
                    name = self.stringvalue()
                elif self.valuefieldid == SID_VERSION:
                    version = self.intvalue()
                elif self.valuefieldid == SID_MAX_ID:
                    maxid = self.intvalue()

            t = self.next()

        self.stepout()

        if name == "" or name == SystemSymbols.ION:
            return

        if version < 1:
            version = 1

        table = self.findcatalogitem(name)
        if maxid < 0:
            _assert(table is not None and version == table.version, "Import %s lacks maxid" % name)
            maxid = len(table.symnames)

        if table is not None:
            self.symbols.import_(table, min(maxid, len(table.symnames)))
        else:
            self.symbols.importunknown(name, maxid)

    def intvalue(self):
        _assert(self.valuetid in [TID_POSINT, TID_NEGINT], "Not an int")

        self.preparevalue()
        return self.value

    def stringvalue(self):
        _assert(self.valuetid == TID_STRING, "Not a string")

        if self.valueisnull:
            return ""

        self.preparevalue()
        return self.value

    def symbolvalue(self):
        _assert(self.valuetid == TID_SYMBOL, "Not a symbol")

        self.preparevalue()
        result = self.symbols.findbyid(self.value)
        if result == "":
            result = "SYMBOL#%d" % self.value
        return result

    def lobvalue(self):
        _assert(self.valuetid in [TID_CLOB, TID_BLOB], "Not a LOB type: %s" % self.getfieldname())

        if self.valueisnull:
            return None

        result = self.read(self.valuelen)
        self.state = ParserState.AfterValue
        return result

    def decimalvalue(self):
        _assert(self.valuetid == TID_DECIMAL, "Not a decimal")

        self.preparevalue()
        return self.value

    def preparevalue(self):
        if self.value is None:
            self.loadscalarvalue()

    def loadscalarvalue(self):
        if self.valuetid not in [TID_NULL, TID_BOOLEAN, TID_POSINT, TID_NEGINT,
                                 TID_FLOAT, TID_DECIMAL, TID_TIMESTAMP,
                                 TID_SYMBOL, TID_STRING]:
            return

        if self.valueisnull:
            self.value = None
            return

        if self.valuetid == TID_STRING:
            self.value = self.read(self.valuelen).decode("UTF-8")

        elif self.valuetid in (TID_POSINT, TID_NEGINT, TID_SYMBOL):
            if self.valuelen == 0:
                self.value = 0
            else:
                _assert(self.valuelen <= 4, "int too long: %d" % self.valuelen)
                v = 0
                for i in range(self.valuelen - 1, -1, -1):
                    v = (v | (bord(self.read()) << (i * 8)))

                if self.valuetid == TID_NEGINT:
                    self.value = -v
                else:
                    self.value = v

        elif self.valuetid == TID_DECIMAL:
            self.value = self.readdecimal()

        #else:
        #    _assert(False, "Unhandled scalar type %d" % self.valuetid)

        self.state = ParserState.AfterValue

    def clearvalue(self):
        self.valuetid = -1
        self.value = None
        self.valueisnull = False
        self.valuefieldid = SID_UNKNOWN
        self.annotations = []

    def loadannotations(self):
        ln = self.readvaruint()
        maxpos = self.stream.tell() + ln
        while self.stream.tell() < maxpos:
            self.annotations.append(self.readvaruint())
        self.valuetid = self.readtypeid()

    def checkversionmarker(self):
        for i in VERSION_MARKER:
            _assert(self.read() == i, "Unknown version marker")

        self.valuelen = 0
        self.valuetid = TID_SYMBOL
        self.value = SID_ION_1_0
        self.valueisnull = False
        self.valuefieldid = SID_UNKNOWN
        self.state = ParserState.AfterValue

    def findcatalogitem(self, name):
        for result in self.catalog:
            if result.name == name:
                return result

    def forceimport(self, symbols):
        item = IonCatalogItem("Forced", 1, symbols)
        self.symbols.import_(item, len(symbols))

    def getfieldname(self):
        if self.valuefieldid == SID_UNKNOWN:
            return ""
        return self.symbols.findbyid(self.valuefieldid)

    def getfieldnamesymbol(self):
        return SymbolToken(self.getfieldname(), self.valuefieldid)

    def gettypename(self):
        if len(self.annotations) == 0:
            return ""

        return self.symbols.findbyid(self.annotations[0])

    @staticmethod
    def printlob(b):
        if b is None:
            return "null"

        result = ""
        for i in b:
            result += ("%02x " % bord(i))

        if len(result) > 0:
            result = result[:-1]
        return result

    def ionwalk(self, supert, indent, lst):
        while self.hasnext():
            if supert == TID_STRUCT:
                L = self.getfieldname() + ":"
            else:
                L = ""

            t = self.next()
            if t in [TID_STRUCT, TID_LIST]:
                if L != "":
                    lst.append(indent + L)
                L = self.gettypename()
                if L != "":
                    lst.append(indent + L + "::")
                if t == TID_STRUCT:
                    lst.append(indent + "{")
                else:
                    lst.append(indent + "[")

                self.stepin()
                self.ionwalk(t, indent + "  ", lst)
                self.stepout()

                if t == TID_STRUCT:
                    lst.append(indent + "}")
                else:
                    lst.append(indent + "]")

            else:
                if t == TID_STRING:
                    L += ('"%s"' % self.stringvalue())
                elif t in [TID_CLOB, TID_BLOB]:
                    L += ("{%s}" % self.printlob(self.lobvalue()))
                elif t == TID_POSINT:
                    L += str(self.intvalue())
                elif t == TID_SYMBOL:
                    tn = self.gettypename()
                    if tn != "":
                        tn += "::"
                    L += tn + self.symbolvalue()
                elif t == TID_DECIMAL:
                    L += str(self.decimalvalue())
                else:
                    L += ("TID %d" % t)
                lst.append(indent + L)

    def print_(self, lst):
        self.reset()
        self.ionwalk(-1, "", lst)


SYM_NAMES = [ 'com.amazon.drm.Envelope@1.0',
              'com.amazon.drm.EnvelopeMetadata@1.0', 'size', 'page_size',
              'encryption_key', 'encryption_transformation',
              'encryption_voucher', 'signing_key', 'signing_algorithm',
              'signing_voucher', 'com.amazon.drm.EncryptedPage@1.0',
              'cipher_text', 'cipher_iv', 'com.amazon.drm.Signature@1.0',
              'data', 'com.amazon.drm.EnvelopeIndexTable@1.0', 'length',
              'offset', 'algorithm', 'encoded', 'encryption_algorithm',
              'hashing_algorithm', 'expires', 'format', 'id',
              'lock_parameters', 'strategy', 'com.amazon.drm.Key@1.0',
              'com.amazon.drm.KeySet@1.0', 'com.amazon.drm.PIDv3@1.0',
              'com.amazon.drm.PlainTextPage@1.0',
              'com.amazon.drm.PlainText@1.0', 'com.amazon.drm.PrivateKey@1.0',
              'com.amazon.drm.PublicKey@1.0', 'com.amazon.drm.SecretKey@1.0',
              'com.amazon.drm.Voucher@1.0', 'public_key', 'private_key',
              'com.amazon.drm.KeyPair@1.0', 'com.amazon.drm.ProtectedData@1.0',
              'doctype', 'com.amazon.drm.EnvelopeIndexTableOffset@1.0',
              'enddoc', 'license_type', 'license', 'watermark', 'key', 'value',
              'com.amazon.drm.License@1.0', 'category', 'metadata',
              'categorized_metadata', 'com.amazon.drm.CategorizedMetadata@1.0',
              'com.amazon.drm.VoucherEnvelope@1.0', 'mac', 'voucher',
              'com.amazon.drm.ProtectedData@2.0',
              'com.amazon.drm.Envelope@2.0',
              'com.amazon.drm.EnvelopeMetadata@2.0',
              'com.amazon.drm.EncryptedPage@2.0',
              'com.amazon.drm.PlainText@2.0', 'compression_algorithm',
              'com.amazon.drm.Compressed@1.0', 'page_index_table',
              'com.amazon.drm.VoucherEnvelope@2.0', 'com.amazon.drm.VoucherEnvelope@3.0' ]

def addprottable(ion):
    ion.addtocatalog("ProtectedData", 1, SYM_NAMES)


def pkcs7pad(msg, blocklen):
    paddinglen = blocklen - len(msg) % blocklen
    padding = bchr(paddinglen) * paddinglen
    return msg + padding


def pkcs7unpad(msg, blocklen):
    _assert(len(msg) % blocklen == 0)

    paddinglen = bord(msg[-1])
    _assert(paddinglen > 0 and paddinglen <= blocklen, "Incorrect padding - Wrong key")
    _assert(msg[-paddinglen:] == bchr(paddinglen) * paddinglen, "Incorrect padding - Wrong key")

    return msg[:-paddinglen]


# every VoucherEnvelope version has a corresponding "word" and magic number, used in obfuscating the shared secret
VOUCHER_VERSION_INFOS = {
    2: [b'Antidisestablishmentarianism', 5],
    3: [b'Floccinaucinihilipilification', 8]
}


# obfuscate shared secret according to the VoucherEnvelope version
def obfuscate(secret, version):
    if version == 1:  # v1 does not use obfuscation
        return secret

    params = VOUCHER_VERSION_INFOS[version]
    word = params[0]
    magic = params[1]

    # extend secret so that its length is divisible by the magic number
    if len(secret) % magic != 0:
        secret = secret + b'\x00' * (magic - len(secret) % magic)

    secret = bytearray(secret)

    obfuscated = bytearray(len(secret))
    wordhash = bytearray(hashlib.sha256(word).digest())

    # shuffle secret and xor it with the first half of the word hash
    for i in range(0, len(secret)):
        index = i // (len(secret) // magic) + magic * (i % (len(secret) // magic))
        obfuscated[index] = secret[i] ^ wordhash[index % 16]

    return obfuscated


class DrmIonVoucher(object):
    envelope = None
    version = None
    voucher = None
    drmkey = None
    license_type = "Unknown"

    encalgorithm = ""
    enctransformation = ""
    hashalgorithm = ""

    lockparams = None

    ciphertext = b""
    cipheriv = b""
    secretkey = b""

    def __init__(self, voucherenv, dsn, secret):
        self.dsn,self.secret = dsn,secret

        self.lockparams = []

        self.envelope = BinaryIonParser(voucherenv)
        addprottable(self.envelope)

    def decryptvoucher(self):
        shared = "PIDv3" + self.encalgorithm + self.enctransformation + self.hashalgorithm

        self.lockparams.sort()
        for param in self.lockparams:
            if param == "ACCOUNT_SECRET":
                shared += param + self.secret
            elif param == "CLIENT_ID":
                shared += param + self.dsn
            else:
                _assert(False, "Unknown lock parameter: %s" % param)

        sharedsecret = obfuscate(shared.encode('ASCII'), self.version)

        key = hmac.new(sharedsecret, "PIDv3", digestmod=hashlib.sha256).digest()
        aes = AES.new(key[:32], AES.MODE_CBC, self.cipheriv[:16])
        b = aes.decrypt(self.ciphertext)
        b = pkcs7unpad(b, 16)

        self.drmkey = BinaryIonParser(BytesIO(b))
        addprottable(self.drmkey)

        _assert(self.drmkey.hasnext() and self.drmkey.next() == TID_LIST and self.drmkey.gettypename() == "com.amazon.drm.KeySet@1.0",
                "Expected KeySet, got %s" % self.drmkey.gettypename())

        self.drmkey.stepin()
        while self.drmkey.hasnext():
            self.drmkey.next()
            if self.drmkey.gettypename() != "com.amazon.drm.SecretKey@1.0":
                continue

            self.drmkey.stepin()
            while self.drmkey.hasnext():
                self.drmkey.next()
                if self.drmkey.getfieldname() == "algorithm":
                    _assert(self.drmkey.stringvalue() == "AES", "Unknown cipher algorithm: %s" % self.drmkey.stringvalue())
                elif self.drmkey.getfieldname() == "format":
                    _assert(self.drmkey.stringvalue() == "RAW", "Unknown key format: %s" % self.drmkey.stringvalue())
                elif self.drmkey.getfieldname() == "encoded":
                    self.secretkey = self.drmkey.lobvalue()

            self.drmkey.stepout()
            break

        self.drmkey.stepout()

    def parse(self):
        self.envelope.reset()
        _assert(self.envelope.hasnext(), "Envelope is empty")
        _assert(self.envelope.next() == TID_STRUCT and str.startswith(self.envelope.gettypename(), "com.amazon.drm.VoucherEnvelope@"),
                "Unknown type encountered in envelope, expected VoucherEnvelope")
        self.version = int(self.envelope.gettypename().split('@')[1][:-2])

        self.envelope.stepin()
        while self.envelope.hasnext():
            self.envelope.next()
            field = self.envelope.getfieldname()
            if field == "voucher":
                self.voucher = BinaryIonParser(BytesIO(self.envelope.lobvalue()))
                addprottable(self.voucher)
                continue
            elif field != "strategy":
                continue

            _assert(self.envelope.gettypename() == "com.amazon.drm.PIDv3@1.0", "Unknown strategy: %s" % self.envelope.gettypename())

            self.envelope.stepin()
            while self.envelope.hasnext():
                self.envelope.next()
                field = self.envelope.getfieldname()
                if field == "encryption_algorithm":
                    self.encalgorithm = self.envelope.stringvalue()
                elif field == "encryption_transformation":
                    self.enctransformation = self.envelope.stringvalue()
                elif field == "hashing_algorithm":
                    self.hashalgorithm = self.envelope.stringvalue()
                elif field == "lock_parameters":
                    self.envelope.stepin()
                    while self.envelope.hasnext():
                        _assert(self.envelope.next() == TID_STRING, "Expected string list for lock_parameters")
                        self.lockparams.append(self.envelope.stringvalue())
                    self.envelope.stepout()

            self.envelope.stepout()

        self.parsevoucher()

    def parsevoucher(self):
        _assert(self.voucher.hasnext(), "Voucher is empty")
        _assert(self.voucher.next() == TID_STRUCT and self.voucher.gettypename() == "com.amazon.drm.Voucher@1.0",
                "Unknown type, expected Voucher")

        self.voucher.stepin()
        while self.voucher.hasnext():
            self.voucher.next()

            if self.voucher.getfieldname() == "cipher_iv":
                self.cipheriv = self.voucher.lobvalue()
            elif self.voucher.getfieldname() == "cipher_text":
                self.ciphertext = self.voucher.lobvalue()
            elif self.voucher.getfieldname() == "license":
                _assert(self.voucher.gettypename() == "com.amazon.drm.License@1.0",
                        "Unknown license: %s" % self.voucher.gettypename())
                self.voucher.stepin()
                while self.voucher.hasnext():
                    self.voucher.next()
                    if self.voucher.getfieldname() == "license_type":
                        self.license_type = self.voucher.stringvalue()
                self.voucher.stepout()

    def printenvelope(self, lst):
        self.envelope.print_(lst)

    def printkey(self, lst):
        if self.voucher is None:
            self.parse()
        if self.drmkey is None:
            self.decryptvoucher()

        self.drmkey.print_(lst)

    def printvoucher(self, lst):
        if self.voucher is None:
            self.parse()

        self.voucher.print_(lst)

    def getlicensetype(self):
        return self.license_type


class DrmIon(object):
    ion = None
    voucher = None
    vouchername = ""
    key = b""
    onvoucherrequired = None

    def __init__(self, ionstream, onvoucherrequired):
        self.ion = BinaryIonParser(ionstream)
        addprottable(self.ion)
        self.onvoucherrequired = onvoucherrequired

    def parse(self, outpages):
        self.ion.reset()

        _assert(self.ion.hasnext(), "DRMION envelope is empty")
        _assert(self.ion.next() == TID_SYMBOL and self.ion.gettypename() == "doctype", "Expected doctype symbol")
        _assert(self.ion.next() == TID_LIST and self.ion.gettypename() in ["com.amazon.drm.Envelope@1.0", "com.amazon.drm.Envelope@2.0"],
                "Unknown type encountered in DRMION envelope, expected Envelope, got %s" % self.ion.gettypename())

        while True:
            if self.ion.gettypename() == "enddoc":
                break

            self.ion.stepin()
            while self.ion.hasnext():
                self.ion.next()

                if self.ion.gettypename() in ["com.amazon.drm.EnvelopeMetadata@1.0", "com.amazon.drm.EnvelopeMetadata@2.0"]:
                    self.ion.stepin()
                    while self.ion.hasnext():
                        self.ion.next()
                        if self.ion.getfieldname() != "encryption_voucher":
                            continue

                        if self.vouchername == "":
                            self.vouchername = self.ion.stringvalue()
                            self.voucher = self.onvoucherrequired(self.vouchername)
                            self.key = self.voucher.secretkey
                            _assert(self.key is not None, "Unable to obtain secret key from voucher")
                        else:
                            _assert(self.vouchername == self.ion.stringvalue(),
                                    "Unexpected: Different vouchers required for same file?")

                    self.ion.stepout()

                elif self.ion.gettypename() in ["com.amazon.drm.EncryptedPage@1.0", "com.amazon.drm.EncryptedPage@2.0"]:
                    decompress = False
                    ct = None
                    civ = None
                    self.ion.stepin()
                    while self.ion.hasnext():
                        self.ion.next()
                        if self.ion.gettypename() == "com.amazon.drm.Compressed@1.0":
                            decompress = True
                        if self.ion.getfieldname() == "cipher_text":
                            ct = self.ion.lobvalue()
                        elif self.ion.getfieldname() == "cipher_iv":
                            civ = self.ion.lobvalue()

                    if ct is not None and civ is not None:
                        self.processpage(ct, civ, outpages, decompress)
                    self.ion.stepout()

            self.ion.stepout()
            if not self.ion.hasnext():
                break
            self.ion.next()

    def print_(self, lst):
        self.ion.print_(lst)

    def processpage(self, ct, civ, outpages, decompress):
        aes = AES.new(self.key[:16], AES.MODE_CBC, civ[:16])
        msg = pkcs7unpad(aes.decrypt(ct), 16)

        if not decompress:
            outpages.write(msg)
            return

        _assert(msg[0] == b"\x00", "LZMA UseFilter not supported")

        if calibre_lzma is not None:
            with calibre_lzma.decompress(msg[1:], bufsize=0x1000000) as f:
                f.seek(0)
                outpages.write(f.read())
            return

        decomp = lzma.LZMADecompressor(format=lzma.FORMAT_ALONE)
        while not decomp.eof:
            segment = decomp.decompress(msg[1:])
            msg = b"" # Contents were internally buffered after the first call
            outpages.write(segment)