15821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)# Copyright (c) 2011 The Chromium Authors. All rights reserved. 25821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)# Use of this source code is governed by a BSD-style license that can be 35821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)# found in the LICENSE file. 45821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 55821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)"""Helper module for ASN.1/DER encoding.""" 65821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 75821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)import binascii 85821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)import struct 95821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)# Tags as defined by ASN.1. 115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)INTEGER = 2 125821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)BIT_STRING = 3 135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)NULL = 5 145821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)OBJECT_IDENTIFIER = 6 155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)SEQUENCE = 0x30 165821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 175821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)def Data(tag, data): 185821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) """Generic type-length-value encoder. 195821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 205821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) Args: 215821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) tag: the tag. 225821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) data: the data for the given tag. 235821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) Returns: 245821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) encoded TLV value. 255821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) """ 265821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) if len(data) == 0: 275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return struct.pack(">BB", tag, 0); 285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) assert len(data) <= 0xffff; 295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return struct.pack(">BBH", tag, 0x82, len(data)) + data; 305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)def Integer(value): 325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) """Encodes an integer. 335821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 345821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) Args: 355821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) value: the long value. 365821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) Returns: 375821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) encoded TLV value. 385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) """ 395821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) data = '%x' % value 405821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return Data(INTEGER, binascii.unhexlify('00' + '0' * (len(data) % 2) + data)) 415821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 425821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)def Bitstring(value): 435821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) """Encodes a bit string. 445821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 455821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) Args: 465821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) value: a string holding the binary data. 475821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) Returns: 485821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) encoded TLV value. 495821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) """ 505821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return Data(BIT_STRING, '\x00' + value) 515821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 525821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)def Sequence(values): 535821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) """Encodes a sequence of other values. 545821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 555821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) Args: 565821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) values: the list of values, must be strings holding already encoded data. 575821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) Returns: 585821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) encoded TLV value. 595821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) """ 605821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return Data(SEQUENCE, ''.join(values)) 61