Re: CRC Duplicate
"NickP" <a@a.com> wrote in message
news:uSlwqS7kHHA.4772@TK2MSFTNGP05.phx.gbl
I understand that a CRC is a unique hash created from an abitary
lengthed array of bytes, and that no 2 CRC's should be alike.
You understand incorrectly. Such a thing would be impossible - there are
many more byte sequences than there are 32-bit numbers. CRC was designed
to protect against random noise in the communication lines: if I recall
correctly, CRC-32 can detect and correct a single flipped bit, is
guaranteed to detect (but not correct) two flipped bits, but two
messages differing in as few as three bits may have the same CRC.
Moreover, since CRC is calculated from a simple formula, it is quite
easy to deliberately generate two messages having the same CRC.
Also, is there such thing as a 256bit CRC?
Depending on what you need to achieve, you may want to look at
cryptographic hashes, such as MD-5, SHA-1, SHA-256 and so on. Such
hashes are usually 16 or 20 bytes large, and are cryptographically
secure: given a hash value, it is computationally unfeasible to find a
message that hashes to this value.
--
With best wishes,
Igor Tandetnik
With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925