CRC32 checksum in Python with hex input

4
votes

I'm wanting to calculate the CRC32 checksum of a string of hex values in python. I found zlib.crc32(data) and binascii.crc32(data), but all the examples I found using these functions have 'data' as a string ('hello' for example). I want to pass hex values in as data and find the checksum. I've tried setting data as a hex value (0x18329a7e for example) and I get a TypeError: must be string or buffer, not int. The function evaluates when I make the hex value a string ('0x18329a7e' for example), but I don't think it's evaluating the correct checksum. Any help would be appreciated. Thanks!

3
pythonstringhexchecksumcrc32
What exactly you mean by "pass hex values in"? Do you realize that hexadecimal is just a numeric representation for humans, and that CRC32 applies to binary data? It is not clear what exactly you want to do: to calculate the CRC32 of a string containing hex characters, or of some binary data that happens to be represented as hexadecimal values somewhere in your software. – Juliano
I want to calculate the CRC32 of some binary data that happens to be represented as hexadecimal values somewhere in my software. – dmranck
Then Andrew's answer does it. – Juliano

3 Answers

12
votes

I think you are looking for binascii.a2b_hex():

>>> binascii.crc32(binascii.a2b_hex('18329a7e'))
-1357533383
1
votes
>>> import struct,binascii
>>> ncrc = lambda numVal: binascii.crc32(struct.pack('!I', numVal))
>>> ncrc(0x18329a7e)
-1357533383
0
votes

Try converting the list of hex values to a string:

t = ['\x18', '\x32', '\x9a', '\x7e']
chksum = binascii.crc32(str(t))