blob: 9040bfe8760401c9684f7f313076a9193ad233c1 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
|
#!/usr/bin/python2.7
# Copyright 2019 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""Helper module for ASN.1/DER encoding."""
import binascii
import struct
# Tags as defined by ASN.1.
INTEGER = 2
BIT_STRING = 3
NULL = 5
OBJECT_IDENTIFIER = 6
SEQUENCE = 0x30
def Data(tag, data):
"""Generic type-length-value encoder.
Args:
tag: the tag.
data: the data for the given tag.
Returns:
encoded TLV value.
"""
if len(data) < 128:
return struct.pack(">BB", tag, len(data)) + data;
assert len(data) <= 0xffff;
return struct.pack(">BBH", tag, 0x82, len(data)) + data;
def Integer(value):
"""Encodes an integer.
Args:
value: the long value.
Returns:
encoded TLV value.
"""
data = '%x' % value
if (len(data) % 2 == 1):
# Odd number of non-zero bytes - pad out our data to a full number of bytes.
data = '0' + data
# If the high bit is set, need to prepend a null byte to denote a positive
# number.
if (int(data[0], 16) >= 8):
data = '00' + data
return Data(INTEGER, binascii.unhexlify(data))
def Bitstring(value):
"""Encodes a bit string.
Args:
value: a string holding the binary data.
Returns:
encoded TLV value.
"""
return Data(BIT_STRING, '\x00' + value)
def Sequence(values):
"""Encodes a sequence of other values.
Args:
values: the list of values, must be strings holding already encoded data.
Returns:
encoded TLV value.
"""
return Data(SEQUENCE, ''.join(values))
|
