manipulating hex values
stephen.cattaneo at u4eatech.com
Tue Apr 1 19:11:31 CEST 2008
I am relatively new to socket programming. I am attempting to use raw
sockets to spoof my IP address. From what I can tell I will have to
build from the Ethernet layer on up. This is fine, but I am having
some trouble with manipulating my hex values.
Seems to me that there are two ways to store hex values:
1. as literal hex - 0x55aa
2. as a string - "\x55aa"
If I want to convert hex to decimal I can use:
int("\x55aa", 16) # note that plain 0x55aa, instead of "\x55aa", will
raise an exception
If I want to do any kind of calculation I have found its best to just
convert my values to decimal, do the math, then convert back to hex. In
my bellow code I get
ValueError: invalid literal for int()"""
when attempting to run. I do not understand why this exception is
being raised? It is a for loop iterating over a list of hex strings.
Sorry for the long-ish question. Any help or comments would be appreciated.
byteList = 
# convert groups from hex to dec
for value in ipHeaders:
byteList.append(int(value,16)) # Exception raised here!
# 1's compliment
for index in range(len(byteList)):
byteList[index] = abs(byteList[index] - 65535)
# add bytes together shifting the extra byte
total = 0
for value in byteList:
total = total + value
if total > 65535:
total = total - 65535
checksum = calcIPChecksum(["\x45" + "\x00", "\x01\x4a", "\x00\x00",
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