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# $Id: ah.py 34 2007-01-28 07:54:20Z dugsong $
# -*- coding: utf-8 -*-
"""Authentication Header."""
from __future__ import absolute_import
from . import dpkt
from . import ip
class AH(dpkt.Packet):
"""Authentication Header.
The Authentication Header (AH) protocol provides data origin authentication, data integrity, and replay protection.
Attributes:
__hdr__: Header fields of AH.
auth: Authentication body.
data: Message data.
"""
__hdr__ = (
('nxt', 'B', 0),
('len', 'B', 0), # payload length
('rsvd', 'H', 0),
('spi', 'I', 0),
('seq', 'I', 0)
)
auth = b''
def unpack(self, buf):
dpkt.Packet.unpack(self, buf)
auth_len = max(4*self.len - 4, 0) # see RFC 4302, section 2.2
self.auth = self.data[:auth_len]
buf = self.data[auth_len:]
try:
self.data = ip.IP.get_proto(self.nxt)(buf)
setattr(self, self.data.__class__.__name__.lower(), self.data)
except (KeyError, dpkt.UnpackError):
self.data = buf
def __len__(self):
return self.__hdr_len__ + len(self.auth) + len(self.data)
def __bytes__(self):
return self.pack_hdr() + bytes(self.auth) + bytes(self.data)
def test_default_creation():
ah = AH()
assert ah.nxt == 0
assert ah.len == 0
assert ah.rsvd == 0
assert ah.spi == 0
assert ah.seq == 0
assert len(ah) == ah.__hdr_len__
assert bytes(ah) == b'\x00' * 12
def test_creation_from_buf():
from binascii import unhexlify
buf_ip = unhexlify(
'04' # IP
'0000000000000000000000'
'4500002200000000401172c001020304'
'01020304006f00de000ebf35666f6f626172'
)
ah = AH(buf_ip)
assert ah.nxt == 4 # IP
assert isinstance(ah.data, ip.IP)
assert len(ah) == 46
assert bytes(ah) == buf_ip
buf_not_ip = unhexlify(
'37' # Not registered
'0000000000000000000000'
'4500002200000000401172c001020304'
'01020304006f00de000ebf35666f6f626172'
)
ah_not_ip = AH(buf_not_ip)
assert ah_not_ip.nxt == 0x37
assert isinstance(ah_not_ip.data, bytes)
assert len(ah_not_ip) == 46
assert bytes(ah_not_ip) == buf_not_ip
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