def toVal(self):
if len(self._payload) > 0 and self._payload[0] >= 0x80:
raise DerDecodingException(
"DerInteger: Negative integers are not currently supported")
result = 0
for i in range(len(self._payload)):
result *= 256
result += self._payload[i]
return result
def getChildren(self):
"""
If this object is a DerSequence, get the children of this node. Otherwise,
raise an exception. (DerSequence overrides to implement this method.)
:return: The children of this node
:rtype: array of DerNode
:raises: DerDecodingException if this object is not a DerSequence.
"""
raise DerDecodingException(
"getChildren: This DerNode is not DerSequence")
def parse(inputBuf, startIdx=0):
"""
Parse the data from the input buffer recursively and return the root as a subclass of DerNode.
:param inputBuf: The input buffer to read from.
:type inputBuf: bytearray or Blob
:param startIdx: (optional) An offset into the buffer.
:type startIdx: int
"""
if isinstance(inputBuf, Blob):
inputBuf = inputBuf.buf()
if len(inputBuf) <= startIdx:
raise DerDecodingException(
"DerNode.parse: The input length is too small")
nodeType = inputBuf[startIdx] # don't increment, we're just peeking
outputType = None
if nodeType == Der.Boolean:
outputType = DerBoolean
elif nodeType == Der.Integer:
outputType = DerInteger
elif nodeType == Der.BitString:
outputType = DerBitString
elif nodeType == Der.OctetString:
outputType = DerOctetString
elif nodeType == Der.Null:
outputType = DerNull
elif nodeType == Der.ObjectIdentifier:
outputType = DerOid
elif nodeType == Der.Sequence:
outputType = DerSequence
elif nodeType == Der.PrintableString:
outputType = DerPrintableString
elif nodeType == Der.GeneralizedTime:
outputType = DerGeneralizedTime
else:
raise DerDecodingException(
"Unimplemented DER type {}".format(nodeType))
newNode = outputType()
newNode.decode(inputBuf, startIdx)
return newNode
def getSequence(children, index):
"""
Check that index is in bounds for the children list, and return
children[index].
:param children: The list of DerNode, usually returned by another
call to getChildren.
:type children: array of DerNode
:param int index: The index of the children.
:return: children[index] which is a DerSequence
:rtype: DerSequence
:raises: DerDecodingException if index is out of bounds or if
children[index] is not a DerSequence.
"""
if index < 0 or index >= len(children):
raise DerDecodingException(
"getSequence: Child index is out of bounds")
if not isinstance(children[index], DerSequence):
raise DerDecodingException(
"getSequence: Child DerNode is not a DerSequence")
return children[index]
def _decodeHeader(self, inputBuf, startIdx=0):
"""
Extracts the header from an input buffer.
:param inputBuf: The input buffer to read from.
:type inputBuf: bytearray or Blob
:param startIdx: (optional) An offset into the buffer.
:type startIdx: int
"""
if isinstance(inputBuf, Blob):
inputBuf = inputBuf.buf()
idx = startIdx
nodeType = inputBuf[idx]
idx += 1
self._nodeType = nodeType
sizeLen = inputBuf[idx]
idx += 1
self._header = bytearray([nodeType, sizeLen])
size = sizeLen
isLongFormat = sizeLen & (1 << 7)
if isLongFormat:
lenCount = sizeLen & ((1 << 7) - 1)
size = 0
while lenCount > 0:
if len(inputBuf) <= idx:
raise DerDecodingException(
"DerNode.decodeHeader: The input length is too small")
b = inputBuf[idx]
idx += 1
self._header.append(b)
size = 256 * size + int(b)
lenCount -= 1
return size