Non-math-geek needs help with CRCs (binascii.crc32)

[Nick Craig-Wood]

nobody <get at bent.com> wrote:
>  1) Does anyone know if the CRC32 algorithm in binascii has a name?  There
>  seem to be a TON of different CRC32 methods; different polynomials,
>  different byte orders, different seeds, some flip the bits and some XOR the
>  result with something else.
> 
>  I've been looking around and a lot of documents (RFCs, etc) refer to ISO3309
>  and/or ITU-T V.42 (neither of which appear to be available without paid
>  access), yet are often incompatible with each other.  So unless they're
>  lying, I assume ISO3309 allows for the above variations, and specifying an
>  ISO3309 CRC32 doesn't narrow it down any.

Look here

  http://www.ross.net/crc/

and in particular here

  http://www.repairfaq.org/filipg/LINK/F_crc_v3.html

For Ross N. Williams's thoughts on CRCs.  Well worth reading IMHO.
You'll find interesting the section on the different way each CRC can
be used (reversed, reflected etc).

If you have a sample of data, its usually pretty easy to work out
which CRC it does actually use by trial and error.  You can use the
code Ross provides to help.

-- 
Nick Craig-Wood
ncw at axis.demon.co.uk