12-19-2007
This will not work, a 32 bit CRC will not fit in "4 bytes of hex". While 32 bits is indeed 4 bytes, a byte has 2^8 (256) possible values; base 256 (haha).
You are implying that the spec is transfering a 32 bit CRC value using "hexidecimal". This effectively reduces the resolution for each byte to 16 values. In doing so, to represent the entire range of 32 bit CRC values it will need 8 hexidecimal "bytes".
More simply stated, the biggest value for a 32 bit CRC is 2^32-1 (hex "FFFFFFFF"). This sequence of hexidecimal characters will occupy 8 bytes if translated verbatim.
Given this, I think you are very confused by something.... I am just not sure what. All the "convert the string and CRC to decimal" [sic] talk makes no sense to me. You have an algorithm that generates a CRC from a piece of data. The receiver should use the same alogoirthm, generate a CRC, and compare against the CRC sent with the data.
If the protocol does something more complicated then you need to understand what that is. For example, you mention a "common key" which I presume is the CRC, but I have no idea.
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LEARN ABOUT DEBIAN
string::crc32
CRC32(3pm) User Contributed Perl Documentation CRC32(3pm)
NAME
String::CRC32 - Perl interface for cyclic redundency check generation
SYNOPSIS
use String::CRC32;
$crc = crc32("some string");
$crc = crc32("some string", initvalue);
$somestring = "some string";
$crc = crc32($somestring);
open(SOMEFILE, "location/of/some.file");
$crc = crc32(*SOMEFILE);
close(SOMEFILE);
DESCRIPTION
The CRC32 module calculates CRC sums of 32 bit lenghts. It generates the same CRC values as ZMODEM, PKZIP, PICCHECK and many others.
Despite its name, this module is able to compute the checksum of files as well as strings.
EXAMPLES
$crc = crc32("some string");
results in the same as
$crc = crc32(" string", crc32("some"));
This is useful for subsequent CRC checking of substrings.
You may even check files:
open(SOMEFILE, "location/of/some.file");
$crc = crc32(*SOMEFILE);
close(SOMEFILE);
A init value may also been supplied in the above example.
AUTHOR
Soenke J. Peters <peters__perl@opcenter.de>
Please be so kind as to report any bugs/suggestions to the above address.
COPYRIGHT
CRC algorithm code taken from CRC-32 by Craig Bruce. The module stuff is inspired by a similar perl module called String::CRC by David
Sharnoff & Matthew Dillon. Horst Fickenscher told me that it could be useful to supply an init value to the crc checking function and so I
included this possibility.
The author of this package disclaims all copyrights and releases it into the public domain.
perl v5.14.2 2005-04-04 CRC32(3pm)