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# scapy.contrib.description = CARP
# scapy.contrib.status = loads
from scapy.packet import *
from scapy.layers.inet import IP
from scapy.fields import BitField, ByteField, XShortField, IntField, XIntField
from scapy.utils import checksum
import struct, hmac, hashlib
class CARP(Packet):
name = "CARP"
fields_desc = [ BitField("version", 4, 4),
BitField("type", 4, 4),
ByteField("vhid", 1),
ByteField("advskew", 0),
ByteField("authlen", 0),
ByteField("demotion", 0),
ByteField("advbase", 0),
XShortField("chksum", 0),
XIntField("counter1", 0),
XIntField("counter2", 0),
XIntField("hmac1", 0),
XIntField("hmac2", 0),
XIntField("hmac3", 0),
XIntField("hmac4", 0),
XIntField("hmac5", 0)
]
def post_build(self, pkt, pay):
if self.chksum == None:
pkt = pkt[:6] + struct.pack("!H", checksum(pkt)) + pkt[8:]
return pkt
def build_hmac_sha1(pkt, pw = '\0' * 20, ip4l = [], ip6l = []):
if not pkt.haslayer(CARP):
return None
p = pkt[CARP]
h = hmac.new(pw, digestmod = hashlib.sha1)
# XXX: this is a dirty hack. it needs to pack version and type into a single 8bit field
h.update('\x21')
# XXX: mac addy if different from special link layer. comes before vhid
h.update(struct.pack('!B', p.vhid))
sl = []
for i in ip4l:
# sort ips from smallest to largest
sl.append(inet_aton(i))
sl.sort()
for i in sl:
h.update(i)
# XXX: do ip6l sorting
return h.digest()
"""
XXX: Usually CARP is multicast to 224.0.0.18 but because of virtual setup, it'll
be unicast between nodes. Uncomment the following line for normal use
bind_layers(IP, CARP, proto=112, dst='224.0.0.18')
"""
bind_layers(IP, CARP, proto=112)
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