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ttt/pywidevine/L3/cdm/vmp.py

103 lines
3.0 KiB

try:
from google.protobuf.internal.decoder import _DecodeVarint as _di # this was tested to work with protobuf 3, but it's an internal API (any varint decoder might work)
except ImportError:
# this is generic and does not depend on pb internals, however it will decode "larger" possible numbers than pb decoder which has them fixed
def LEB128_decode(buffer, pos, limit = 64):
result = 0
shift = 0
while True:
b = buffer[pos]
pos += 1
result |= ((b & 0x7F) << shift)
if not (b & 0x80):
return (result, pos)
shift += 7
if shift > limit:
raise Exception("integer too large, shift: {}".format(shift))
_di = LEB128_decode
class FromFileMixin:
@classmethod
def from_file(cls, filename):
"""Load given a filename"""
with open(filename,"rb") as f:
return cls(f.read())
# the signatures use a format internally similar to
# protobuf's encoding, but without wire types
class VariableReader(FromFileMixin):
"""Protobuf-like encoding reader"""
def __init__(self, buf):
self.buf = buf
self.pos = 0
self.size = len(buf)
def read_int(self):
"""Read a variable length integer"""
# _DecodeVarint will take care of out of range errors
(val, nextpos) = _di(self.buf, self.pos)
self.pos = nextpos
return val
def read_bytes_raw(self, size):
"""Read size bytes"""
b = self.buf[self.pos:self.pos+size]
self.pos += size
return b
def read_bytes(self):
"""Read a bytes object"""
size = self.read_int()
return self.read_bytes_raw(size)
def is_end(self):
return (self.size == self.pos)
class TaggedReader(VariableReader):
"""Tagged reader, needed for implementing a WideVine signature reader"""
def read_tag(self):
"""Read a tagged buffer"""
return (self.read_int(), self.read_bytes())
def read_all_tags(self, max_tag=3):
tags = {}
while (not self.is_end()):
(tag, bytes) = self.read_tag()
if (tag > max_tag):
raise IndexError("tag out of bound: got {}, max {}".format(tag, max_tag))
tags[tag] = bytes
return tags
class WideVineSignatureReader(FromFileMixin):
"""Parses a widevine .sig signature file."""
SIGNER_TAG = 1
SIGNATURE_TAG = 2
ISMAINEXE_TAG = 3
def __init__(self, buf):
reader = TaggedReader(buf)
self.version = reader.read_int()
if (self.version != 0):
raise Exception("Unsupported signature format version {}".format(self.version))
self.tags = reader.read_all_tags()
self.signer = self.tags[self.SIGNER_TAG]
self.signature = self.tags[self.SIGNATURE_TAG]
extra = self.tags[self.ISMAINEXE_TAG]
if (len(extra) != 1 or (extra[0] > 1)):
raise Exception("Unexpected 'ismainexe' field value (not '\\x00' or '\\x01'), please check: {0}".format(extra))
self.mainexe = bool(extra[0])
@classmethod
def get_tags(cls, filename):
"""Return a dictionary of each tag in the signature file"""
return cls.from_file(filename).tags