blob: 618e8559c9be08417d26ccddf910538f0a57d919 [file] [log] [blame]
# Author: Trevor Perrin
# Patch from Google adding getChildBytes()
#
# See the LICENSE file for legal information regarding use of this file.
"""Class for parsing ASN.1"""
from .compat import *
from .codec import *
#Takes a byte array which has a DER TLV field at its head
class ASN1Parser(object):
def __init__(self, bytes):
p = Parser(bytes)
p.get(1) #skip Type
#Get Length
self.length = self._getASN1Length(p)
#Get Value
self.value = p.getFixBytes(self.length)
#Assuming this is a sequence...
def getChild(self, which):
return ASN1Parser(self.getChildBytes(which))
def getChildBytes(self, which):
p = Parser(self.value)
for x in range(which+1):
markIndex = p.index
p.get(1) #skip Type
length = self._getASN1Length(p)
p.getFixBytes(length)
return p.bytes[markIndex : p.index]
#Decode the ASN.1 DER length field
def _getASN1Length(self, p):
firstLength = p.get(1)
if firstLength<=127:
return firstLength
else:
lengthLength = firstLength & 0x7F
return p.get(lengthLength)