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"""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:
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):
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 ASN1Parser(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)
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