35 lines
960 B
Python
35 lines
960 B
Python
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"""Class for parsing ASN.1"""
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from compat import *
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from codec import *
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#Takes a byte array which has a DER TLV field at its head
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class ASN1Parser:
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def __init__(self, bytes):
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p = Parser(bytes)
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p.get(1) #skip Type
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#Get Length
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self.length = self._getASN1Length(p)
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#Get Value
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self.value = p.getFixBytes(self.length)
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#Assuming this is a sequence...
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def getChild(self, which):
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p = Parser(self.value)
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for x in range(which+1):
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markIndex = p.index
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p.get(1) #skip Type
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length = self._getASN1Length(p)
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p.getFixBytes(length)
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return ASN1Parser(p.bytes[markIndex : p.index])
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#Decode the ASN.1 DER length field
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def _getASN1Length(self, p):
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firstLength = p.get(1)
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if firstLength<=127:
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return firstLength
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else:
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lengthLength = firstLength & 0x7F
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return p.get(lengthLength)
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