DeDRM_tools/dedrm_src/ion.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Pascal implementation by lulzkabulz. Python translation by apprenticenaomi. DeDRM integration by anon.
# BinaryIon.pas + DrmIon.pas + IonSymbols.pas

from __future__ import with_statement

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

try:
    from cStringIO import StringIO
except ImportError:
    from StringIO import StringIO

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

try:
    # lzma library from calibre 2.35.0 or later
    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', 'priority', 'refines']

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]


class DrmIonVoucher(object):
    envelope = 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 = shared.encode("UTF-8")

        key = hmac.new(sharedsecret, sharedsecret[:5], 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(StringIO(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 self.envelope.gettypename() == "com.amazon.drm.VoucherEnvelope@1.0",
                "Unknown type encountered in envelope, expected VoucherEnvelope")

        self.envelope.stepin()
        while self.envelope.hasnext():
            self.envelope.next()
            field = self.envelope.getfieldname()
            if field == "voucher":
                self.voucher = BinaryIonParser(StringIO(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)