287 lines
12 KiB
Python
287 lines
12 KiB
Python
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# -*- coding: ascii -*-
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#
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# Util/asn1.py : Minimal support for ASN.1 DER binary encoding.
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#
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# ===================================================================
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# The contents of this file are dedicated to the public domain. To
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# the extent that dedication to the public domain is not available,
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# everyone is granted a worldwide, perpetual, royalty-free,
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# non-exclusive license to exercise all rights associated with the
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# contents of this file for any purpose whatsoever.
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# No rights are reserved.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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# SOFTWARE.
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# ===================================================================
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from Crypto.Util.number import long_to_bytes, bytes_to_long
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import sys
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from Crypto.Util.py3compat import *
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__all__ = [ 'DerObject', 'DerInteger', 'DerOctetString', 'DerNull', 'DerSequence', 'DerObjectId' ]
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class DerObject:
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"""Base class for defining a single DER object.
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Instantiate this class ONLY when you have to decode a DER element.
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"""
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# Known TAG types
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typeTags = { 'SEQUENCE': 0x30, 'BIT STRING': 0x03, 'INTEGER': 0x02,
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'OCTET STRING': 0x04, 'NULL': 0x05, 'OBJECT IDENTIFIER': 0x06 }
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def __init__(self, ASN1Type=None, payload=b('')):
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"""Initialize the DER object according to a specific type.
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The ASN.1 type is either specified as the ASN.1 string (e.g.
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'SEQUENCE'), directly with its numerical tag or with no tag
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at all (None)."""
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if isInt(ASN1Type) or ASN1Type is None:
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self.typeTag = ASN1Type
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else:
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if len(ASN1Type)==1:
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self.typeTag = ord(ASN1Type)
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else:
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self.typeTag = self.typeTags.get(ASN1Type)
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self.payload = payload
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def isType(self, ASN1Type):
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return self.typeTags[ASN1Type]==self.typeTag
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def _lengthOctets(self, payloadLen):
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"""Return a byte string that encodes the given payload length (in
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bytes) in a format suitable for a DER length tag (L).
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"""
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if payloadLen>127:
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encoding = long_to_bytes(payloadLen)
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return bchr(len(encoding)+128) + encoding
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return bchr(payloadLen)
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def encode(self):
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"""Return a complete DER element, fully encoded as a TLV."""
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return bchr(self.typeTag) + self._lengthOctets(len(self.payload)) + self.payload
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def _decodeLen(self, idx, der):
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"""Given a (part of a) DER element, and an index to the first byte of
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a DER length tag (L), return a tuple with the payload size,
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and the index of the first byte of the such payload (V).
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Raises a ValueError exception if the DER length is invalid.
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Raises an IndexError exception if the DER element is too short.
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"""
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length = bord(der[idx])
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if length<=127:
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return (length,idx+1)
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payloadLength = bytes_to_long(der[idx+1:idx+1+(length & 0x7F)])
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if payloadLength<=127:
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raise ValueError("Not a DER length tag.")
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return (payloadLength, idx+1+(length & 0x7F))
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def decode(self, derEle, noLeftOvers=0):
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"""Decode a complete DER element, and re-initializes this
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object with it.
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@param derEle A complete DER element. It must start with a DER T
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tag.
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@param noLeftOvers Indicate whether it is acceptable to complete the
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parsing of the DER element and find that not all
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bytes in derEle have been used.
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@return Index of the first unused byte in the given DER element.
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Raises a ValueError exception in case of parsing errors.
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Raises an IndexError exception if the DER element is too short.
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"""
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try:
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self.typeTag = bord(derEle[0])
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if (self.typeTag & 0x1F)==0x1F:
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raise ValueError("Unsupported DER tag")
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(length,idx) = self._decodeLen(1, derEle)
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if noLeftOvers and len(derEle) != (idx+length):
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raise ValueError("Not a DER structure")
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self.payload = derEle[idx:idx+length]
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except IndexError:
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raise ValueError("Not a valid DER SEQUENCE.")
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return idx+length
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class DerInteger(DerObject):
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def __init__(self, value = 0):
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"""Class to model an INTEGER DER element.
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Limitation: only non-negative values are supported.
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"""
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DerObject.__init__(self, 'INTEGER')
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self.value = value
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def encode(self):
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"""Return a complete INTEGER DER element, fully encoded as a TLV."""
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self.payload = long_to_bytes(self.value)
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if bord(self.payload[0])>127:
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self.payload = bchr(0x00) + self.payload
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return DerObject.encode(self)
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def decode(self, derEle, noLeftOvers=0):
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"""Decode a complete INTEGER DER element, and re-initializes this
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object with it.
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@param derEle A complete INTEGER DER element. It must start with a DER
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INTEGER tag.
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@param noLeftOvers Indicate whether it is acceptable to complete the
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parsing of the DER element and find that not all
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bytes in derEle have been used.
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@return Index of the first unused byte in the given DER element.
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Raises a ValueError exception if the DER element is not a
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valid non-negative INTEGER.
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Raises an IndexError exception if the DER element is too short.
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"""
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tlvLength = DerObject.decode(self, derEle, noLeftOvers)
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if self.typeTag!=self.typeTags['INTEGER']:
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raise ValueError ("Not a DER INTEGER.")
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if bord(self.payload[0])>127:
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raise ValueError ("Negative INTEGER.")
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self.value = bytes_to_long(self.payload)
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return tlvLength
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class DerSequence(DerObject):
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"""Class to model a SEQUENCE DER element.
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This object behave like a dynamic Python sequence.
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Sub-elements that are INTEGERs, look like Python integers.
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Any other sub-element is a binary string encoded as the complete DER
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sub-element (TLV).
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"""
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def __init__(self, startSeq=None):
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"""Initialize the SEQUENCE DER object. Always empty
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initially."""
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DerObject.__init__(self, 'SEQUENCE')
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if startSeq==None:
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self._seq = []
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else:
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self._seq = startSeq
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## A few methods to make it behave like a python sequence
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def __delitem__(self, n):
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del self._seq[n]
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def __getitem__(self, n):
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return self._seq[n]
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def __setitem__(self, key, value):
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self._seq[key] = value
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def __setslice__(self,i,j,sequence):
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self._seq[i:j] = sequence
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def __delslice__(self,i,j):
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del self._seq[i:j]
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def __getslice__(self, i, j):
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return self._seq[max(0, i):max(0, j)]
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def __len__(self):
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return len(self._seq)
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def append(self, item):
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return self._seq.append(item)
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def hasInts(self):
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"""Return the number of items in this sequence that are numbers."""
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return len(list(filter(isInt, self._seq)))
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def hasOnlyInts(self):
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"""Return True if all items in this sequence are numbers."""
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return self._seq and self.hasInts()==len(self._seq)
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def encode(self):
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"""Return the DER encoding for the ASN.1 SEQUENCE, containing
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the non-negative integers and longs added to this object.
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Limitation: Raises a ValueError exception if it some elements
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in the sequence are neither Python integers nor complete DER INTEGERs.
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"""
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self.payload = b('')
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for item in self._seq:
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try:
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self.payload += item
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except:
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try:
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self.payload += DerInteger(item).encode()
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except:
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raise ValueError("Trying to DER encode an unknown object")
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return DerObject.encode(self)
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def decode(self, derEle, noLeftOvers=0):
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"""Decode a complete SEQUENCE DER element, and re-initializes this
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object with it.
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@param derEle A complete SEQUENCE DER element. It must start with a DER
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SEQUENCE tag.
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@param noLeftOvers Indicate whether it is acceptable to complete the
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parsing of the DER element and find that not all
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bytes in derEle have been used.
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@return Index of the first unused byte in the given DER element.
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DER INTEGERs are decoded into Python integers. Any other DER
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element is not decoded. Its validity is not checked.
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Raises a ValueError exception if the DER element is not a
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valid DER SEQUENCE.
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Raises an IndexError exception if the DER element is too short.
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"""
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self._seq = []
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try:
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tlvLength = DerObject.decode(self, derEle, noLeftOvers)
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if self.typeTag!=self.typeTags['SEQUENCE']:
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raise ValueError("Not a DER SEQUENCE.")
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# Scan one TLV at once
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idx = 0
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while idx<len(self.payload):
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typeTag = bord(self.payload[idx])
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if typeTag==self.typeTags['INTEGER']:
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newInteger = DerInteger()
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idx += newInteger.decode(self.payload[idx:])
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self._seq.append(newInteger.value)
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else:
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itemLen,itemIdx = self._decodeLen(idx+1,self.payload)
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self._seq.append(self.payload[idx:itemIdx+itemLen])
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idx = itemIdx + itemLen
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except IndexError:
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raise ValueError("Not a valid DER SEQUENCE.")
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return tlvLength
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class DerOctetString(DerObject):
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def __init__(self, value = b('')):
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DerObject.__init__(self, 'OCTET STRING')
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self.payload = value
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def decode(self, derEle, noLeftOvers=0):
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p = DerObject.decode(derEle, noLeftOvers)
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if not self.isType("OCTET STRING"):
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raise ValueError("Not a valid OCTET STRING.")
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return p
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class DerNull(DerObject):
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def __init__(self):
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DerObject.__init__(self, 'NULL')
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class DerObjectId(DerObject):
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def __init__(self):
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DerObject.__init__(self, 'OBJECT IDENTIFIER')
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def decode(self, derEle, noLeftOvers=0):
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p = DerObject.decode(derEle, noLeftOvers)
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if not self.isType("OBJECT IDENTIFIER"):
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raise ValueError("Not a valid OBJECT IDENTIFIER.")
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return p
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def isInt(x):
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test = 0
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try:
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test += x
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except TypeError:
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return 0
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return 1
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