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Mail Jürgen Helbing
Error Detection (CRC32)
February, 2002
In order to detect if a file has been corrupted during transmission what is usually done is to calculate a digitial "signature". This is done at the poster's end, and the signature is transmitted along with the file to the receiver. The receiver also calculates the file's digital signature and checks if it's the same as the one that the poster supplied. If they match then the file has come through uncorrupted.

What is CRC32?
CRC stands for Cyclic Redundancy Check. The 32 comes from the fact it calculates a 32-bit checksum. CRC32 is an algorithm for calculating a unique identifier for a file. CRC32 is widely implemented, and also used in programs like PKZIP to identify files and make sure that they are original.

There's 1 in 2^32 chance of two files getting the same CRC32 checksum and being mistaken as being the same file.

CRC's have the interesting property that they will detect ALL single burst error events of their size or less regardless of location.



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