src/third_party/tlslite/tlslite/utils/ASN1Parser.py

   1 """Class for parsing ASN.1"""
   2 from compat import *
   3 from codec import *
   4
   5 #Takes a byte array which has a DER TLV field at its head
   6 class ASN1Parser:
   7     def __init__(self, bytes):
   8         p = Parser(bytes)
   9         p.get(1) #skip Type
  10
  11         #Get Length
  12         self.length = self._getASN1Length(p)
  13
  14         #Get Value
  15         self.value = p.getFixBytes(self.length)
  16
  17     #Assuming this is a sequence...
  18     def getChild(self, which):
  19         return ASN1Parser(self.getChildBytes(which))
  20
  21     def getChildBytes(self, which):
  22         p = Parser(self.value)
  23         for x in range(which+1):
  24             markIndex = p.index
  25             p.get(1) #skip Type
  26             length = self._getASN1Length(p)
  27             p.getFixBytes(length)
  28         return p.bytes[markIndex : p.index]
  29
  30     #Decode the ASN.1 DER length field
  31     def _getASN1Length(self, p):
  32         firstLength = p.get(1)
  33         if firstLength<=127:
  34             return firstLength
  35         else:
  36             lengthLength = firstLength & 0x7F
  37             return p.get(lengthLength)