def calculate_and_set_checksum(ip):
"""
This function calculates tcp, udp and ip checksums and sets the corresponding packet field to this value
:param ip: ip objects, loaded using dpkt library
:return: checksum, packet buffer with set checksum
"""
if ip.v == 4:
IP_MF = 0x2000
IP_OFFMASK = 0x1fff
# set checksum field to zero
ip.data.sum = 0
if (ip.p == 6 or ip.p == 17) and (ip.off & (IP_MF | IP_OFFMASK)) == 0 and \
isinstance(ip.data, dpkt.Packet) and ip.data.sum == 0:
# Set zeroed TCP and UDP checksums for non-fragments.
p = bytes(ip.data)
s = dpkt.struct.pack('>4s4sxBH', ip.src, ip.dst, ip.p, len(p))
s = dpkt.in_cksum_add(0, s)
s = dpkt.in_cksum_add(s, p)
# ip.data.sum = dpkt.in_cksum_done(s)
sum = dpkt.in_cksum_done(s)
if ip.p == 17 and sum == 0:
sum = 0xffff # RFC 768
# XXX - skdada transports which don't need the pseudoheader
return sum, p
elif ip.v == 6:
# XXX - set TCP, UDP, and ICMPv6 checksums
# if (ip.p == 6 or ip.p == 17 or ip.p == 58) and ip.data.sum == None:
if (ip.p == 6 or ip.p == 17): # 6: TCP, 7: UDP
# ip.data.sum = None
# set checksum field to zero
ip.data = bytearray(bytes(ip.data))
if ip.p == 6:
ip.data[16] = 0
ip.data[17] = 0
elif ip.p == 17:
ip.data[6] = 0
ip.data[7] = 0
p = bytes(ip.data)
s = dpkt.struct.pack('>16s16sxBH', ip.src, ip.dst, ip.nxt, len(p))
s = dpkt.in_cksum_add(0, s)
s = dpkt.in_cksum_add(s, p)
try:
return dpkt.in_cksum_done(s), p
except AttributeError:
return None
else:
print('no IP?')
return None
def __str__(self):
if (self.nxt == 6 or self.nxt == 17 or self.nxt == 58) and not self.data.sum:
# XXX - set TCP, UDP, and ICMPv6 checksums
p = str(self.data)
s = dpkt.in_cksum_add(0, self.src + self.dst)
s = dpkt.in_cksum_add(s, p)
try:
self.data.sum = dpkt.in_cksum_done(s + self.nxt + len(p))
except AttributeError:
pass
return dpkt.Packet.__str__(self)
def __str__(self):
if (self.nxt == 6 or self.nxt == 17 or self.nxt == 58) and \
not self.data.sum:
# XXX - set TCP, UDP, and ICMPv6 checksums
p = str(self.data)
s = dpkt.in_cksum_add(0, self.src + self.dst)
s = dpkt.in_cksum_add(s, p)
try:
self.data.sum = dpkt.in_cksum_done(s + self.nxt + len(p))
except AttributeError:
pass
return dpkt.Packet.__str__(self)
def __str__(self):
if (self.nxt == 6 or self.nxt == 17 or self.nxt == 58) and not self.data.sum:
# XXX - set TCP, UDP, and ICMPv6 checksums
p = str(self.data)
s = dpkt.struct.pack('>16s16sxBH', self.src, self.dst, self.nxt, len(p))
s = dpkt.in_cksum_add(0, s)
s = dpkt.in_cksum_add(s, p)
try:
self.data.sum = dpkt.in_cksum_done(s)
except AttributeError:
pass
return self.pack_hdr() + self.headers_str() + str(self.data)
def __str__(self):
if (self.p == 6 or self.p == 17 or self.p == 58) and not self.data.sum:
# XXX - set TCP, UDP, and ICMPv6 checksums
p = str(self.data)
s = dpkt.struct.pack('>16s16sxBH', self.src, self.dst, self.nxt,
len(p))
s = dpkt.in_cksum_add(0, s)
s = dpkt.in_cksum_add(s, p)
try:
self.data.sum = dpkt.in_cksum_done(s)
except AttributeError:
pass
return self.pack_hdr() + self.headers_str() + str(self.data)
def __verify_checksums(cls, ippacket):
if dpkt.in_cksum(ippacket.pack_hdr() + str(ippacket.opts)) != 0:
return False
if (ippacket.off & (dpkt.ip.IP_MF | dpkt.ip.IP_OFFMASK)) != 0:
return True
p = str(ippacket.data)
s = dpkt.struct.pack('>4s4sxBH', ippacket.src, ippacket.dst,
ippacket.p, len(p))
s = dpkt.in_cksum_add(0, s)
s = dpkt.in_cksum_add(s, p)
return dpkt.in_cksum_done(s) == 0
def __str__(self):
if self.sum == 0:
self.sum = dpkt.in_cksum(self.pack_hdr() + str(self.opts))
if (self.p == 6 or self.p == 17) and (self.off & (IP_MF | IP_OFFMASK)) == 0 and \
isinstance(self.data, dpkt.Packet) and self.data.sum == 0:
# Set zeroed TCP and UDP checksums for non-fragments.
p = str(self.data)
s = dpkt.struct.pack('>4s4sxBH', self.src, self.dst,
self.p, len(p))
s = dpkt.in_cksum_add(0, s)
s = dpkt.in_cksum_add(s, p)
self.data.sum = dpkt.in_cksum_done(s)
if self.p == 17 and self.data.sum == 0:
self.data.sum = 0xffff # RFC 768
# XXX - skip transports which don't need the pseudoheader
return self.pack_hdr() + str(self.opts) + str(self.data)
def __str__(self):
if self.sum == 0:
self.sum = dpkt.in_cksum(self.pack_hdr() + self.opts)
if (self.p == 6 or self.p == 17) and (self.off & (IP_MF | IP_OFFMASK)) == 0 and \
isinstance(self.data, dpkt.Packet) and self.data.sum == 0:
# Set zeroed TCP and UDP checksums for non-fragments.
p = str(self.data)
s = dpkt.struct.pack('>4s4sxBH', self.src, self.dst,
self.p, len(p))
s = dpkt.in_cksum_add(0, s)
s = dpkt.in_cksum_add(s, p)
self.data.sum = dpkt.in_cksum_done(s)
if self.p == 17 and self.data.sum == 0:
self.data.sum = 0xffff # RFC 768
# XXX - skip transports which don't need the pseudoheader
return self.pack_hdr() + self.opts + str(self.data)