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Þ'¯°ÌME[YéïĵÂCå½ Ué©Áû'Ê9%eÔðNU”ë‘ÌsD3/®+UI˜9h.WC”빓$#:pz:YÓ ¿xž* ³$Í +$kñAŠ‹†¢ Uê>¸)_š¬÷©ßAÂÔb9ÇU ¯¾á•9¯ÏÏ÷O÷¼¼Fähal1‰3Ì[Ïr•´UCksNÐ] R‘¸¥H+§Šé†c©vÖÞ0iÓ76s†î!§=ß ¼~Ô'°Ãmäoäš³ªøi1úÉ)³yV8 CLÄØÁ‘WYïi€H6ÖÑiámø^ÈY´°Ñ7¥Û*—Ñ©L«Qƒï—Ùrÿ ›£Ð*š¸ˆL©ˆ$ˆ ÷¾D§9È®«qbqC)–ˆïv´çñsÑVT­Ø, <àïºÀO«Jý·õ àfPìð .wFšir´þ’2_Y *Æ€x\« ì€9š@ Ž|F⇥ˆkZ@hÖÄ0t¿-<“‹qµ¾*ZL¤Ú)&BJpÓF5=$„at*Zš$’ÑtdûÝRI1 2Ž‰$€$I$#‰SÞ’Hë¬ï;Á$¡t$’`<(ñÇt)$‡Ð.Êf¢X’Kt=Éé$‚ˆªè¢oÝëòI%Rgcª÷ŠyI%¡‰ÿ !ñ)´õ $¤ Ô’IIGÿÙ# coding: utf-8 """ Functions for parsing and dumping using the ASN.1 DER encoding. Exports the following items: - emit() - parse() - peek() Other type classes are defined that help compose the types listed above. """ from __future__ import unicode_literals, division, absolute_import, print_function import sys from ._types import byte_cls, chr_cls, type_name from .util import int_from_bytes, int_to_bytes _PY2 = sys.version_info <= (3,) _INSUFFICIENT_DATA_MESSAGE = 'Insufficient data - %s bytes requested but only %s available' _MAX_DEPTH = 10 def emit(class_, method, tag, contents): """ Constructs a byte string of an ASN.1 DER-encoded value This is typically not useful. Instead, use one of the standard classes from asn1crypto.core, or construct a new class with specific fields, and call the .dump() method. :param class_: An integer ASN.1 class value: 0 (universal), 1 (application), 2 (context), 3 (private) :param method: An integer ASN.1 method value: 0 (primitive), 1 (constructed) :param tag: An integer ASN.1 tag value :param contents: A byte string of the encoded byte contents :return: A byte string of the ASN.1 DER value (header and contents) """ if not isinstance(class_, int): raise TypeError('class_ must be an integer, not %s' % type_name(class_)) if class_ < 0 or class_ > 3: raise ValueError('class_ must be one of 0, 1, 2 or 3, not %s' % class_) if not isinstance(method, int): raise TypeError('method must be an integer, not %s' % type_name(method)) if method < 0 or method > 1: raise ValueError('method must be 0 or 1, not %s' % method) if not isinstance(tag, int): raise TypeError('tag must be an integer, not %s' % type_name(tag)) if tag < 0: raise ValueError('tag must be greater than zero, not %s' % tag) if not isinstance(contents, byte_cls): raise TypeError('contents must be a byte string, not %s' % type_name(contents)) return _dump_header(class_, method, tag, contents) + contents def parse(contents, strict=False): """ Parses a byte string of ASN.1 BER/DER-encoded data. This is typically not useful. Instead, use one of the standard classes from asn1crypto.core, or construct a new class with specific fields, and call the .load() class method. :param contents: A byte string of BER/DER-encoded data :param strict: A boolean indicating if trailing data should be forbidden - if so, a ValueError will be raised when trailing data exists :raises: ValueError - when the contents do not contain an ASN.1 header or are truncated in some way TypeError - when contents is not a byte string :return: A 6-element tuple: - 0: integer class (0 to 3) - 1: integer method - 2: integer tag - 3: byte string header - 4: byte string content - 5: byte string trailer """ if not isinstance(contents, byte_cls): raise TypeError('contents must be a byte string, not %s' % type_name(contents)) contents_len = len(contents) info, consumed = _parse(contents, contents_len) if strict and consumed != contents_len: raise ValueError('Extra data - %d bytes of trailing data were provided' % (contents_len - consumed)) return info def peek(contents): """ Parses a byte string of ASN.1 BER/DER-encoded data to find the length This is typically used to look into an encoded value to see how long the next chunk of ASN.1-encoded data is. Primarily it is useful when a value is a concatenation of multiple values. :param contents: A byte string of BER/DER-encoded data :raises: ValueError - when the contents do not contain an ASN.1 header or are truncated in some way TypeError - when contents is not a byte string :return: An integer with the number of bytes occupied by the ASN.1 value """ if not isinstance(contents, byte_cls): raise TypeError('contents must be a byte string, not %s' % type_name(contents)) info, consumed = _parse(contents, len(contents)) return consumed def _parse(encoded_data, data_len, pointer=0, lengths_only=False, depth=0): """ Parses a byte string into component parts :param encoded_data: A byte string that contains BER-encoded data :param data_len: The integer length of the encoded data :param pointer: The index in the byte string to parse from :param lengths_only: A boolean to cause the call to return a 2-element tuple of the integer number of bytes in the header and the integer number of bytes in the contents. Internal use only. :param depth: The recursion depth when evaluating indefinite-length encoding. :return: A 2-element tuple: - 0: A tuple of (class_, method, tag, header, content, trailer) - 1: An integer indicating how many bytes were consumed """ if depth > _MAX_DEPTH: raise ValueError('Indefinite-length recursion limit exceeded') start = pointer if data_len < pointer + 1: raise ValueError(_INSUFFICIENT_DATA_MESSAGE % (1, data_len - pointer)) first_octet = ord(encoded_data[pointer]) if _PY2 else encoded_data[pointer] pointer += 1 tag = first_octet & 31 constructed = (first_octet >> 5) & 1 # Base 128 length using 8th bit as continuation indicator if tag == 31: tag = 0 while True: if data_len < pointer + 1: raise ValueError(_INSUFFICIENT_DATA_MESSAGE % (1, data_len - pointer)) num = ord(encoded_data[pointer]) if _PY2 else encoded_data[pointer] pointer += 1 if num == 0x80 and tag == 0: raise ValueError('Non-minimal tag encoding') tag *= 128 tag += num & 127 if num >> 7 == 0: break if tag < 31: raise ValueError('Non-minimal tag encoding') if data_len < pointer + 1: raise ValueError(_INSUFFICIENT_DATA_MESSAGE % (1, data_len - pointer)) length_octet = ord(encoded_data[pointer]) if _PY2 else encoded_data[pointer] pointer += 1 trailer = b'' if length_octet >> 7 == 0: contents_end = pointer + (length_octet & 127) else: length_octets = length_octet & 127 if length_octets: if data_len < pointer + length_octets: raise ValueError(_INSUFFICIENT_DATA_MESSAGE % (length_octets, data_len - pointer)) pointer += length_octets contents_end = pointer + int_from_bytes(encoded_data[pointer - length_octets:pointer], signed=False) else: # To properly parse indefinite length values, we need to scan forward # parsing headers until we find a value with a length of zero. If we # just scanned looking for \x00\x00, nested indefinite length values # would not work. if not constructed: raise ValueError('Indefinite-length element must be constructed') contents_end = pointer while data_len < contents_end + 2 or encoded_data[contents_end:contents_end+2] != b'\x00\x00': _, contents_end = _parse(encoded_data, data_len, contents_end, lengths_only=True, depth=depth+1) contents_end += 2 trailer = b'\x00\x00' if contents_end > data_len: raise ValueError(_INSUFFICIENT_DATA_MESSAGE % (contents_end - pointer, data_len - pointer)) if lengths_only: return (pointer, contents_end) return ( ( first_octet >> 6, constructed, tag, encoded_data[start:pointer], encoded_data[pointer:contents_end-len(trailer)], trailer ), contents_end ) def _dump_header(class_, method, tag, contents): """ Constructs the header bytes for an ASN.1 object :param class_: An integer ASN.1 class value: 0 (universal), 1 (application), 2 (context), 3 (private) :param method: An integer ASN.1 method value: 0 (primitive), 1 (constructed) :param tag: An integer ASN.1 tag value :param contents: A byte string of the encoded byte contents :return: A byte string of the ASN.1 DER header """ header = b'' id_num = 0 id_num |= class_ << 6 id_num |= method << 5 if tag >= 31: cont_bit = 0 while tag > 0: header = chr_cls(cont_bit | (tag & 0x7f)) + header if not cont_bit: cont_bit = 0x80 tag = tag >> 7 header = chr_cls(id_num | 31) + header else: header += chr_cls(id_num | tag) length = len(contents) if length <= 127: header += chr_cls(length) else: length_bytes = int_to_bytes(length) header += chr_cls(0x80 | len(length_bytes)) header += length_bytes return header