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CRC or Checksum or XOR or DES

Posted on 2001-07-11
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Last Modified: 2007-02-12
Hi,

There is any part or someone that can tell me what is the difference between them and what is the advantages of each one ??

I need to know how they work and if they are efficience.

Thank you
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Question by:arocio
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by:Droby10
ID: 6275969
crc (cyclical redundancy check) is most comonly used as data verification in the form of a parity bit...it is mostly used for handling data transfers from modulated or spindle devices; crc represents a form of checksum...but you could also say that an md5 hash is a checksum, which in no way resembles a crc value.

xor is a binary function performed on two values.
1 xor 255 = 254, 128 xor 128 = 0, 128 xor 127 = 255...

des is a shared key cryptography system...some of the algorithms used in des make use of xor.
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tonimargiotta earned 100 total points
ID: 6343764
A check sum is a hash, a piece of data derived by an alogorithm from a larger piece of data.  Which algorithm you choose will depend on the use you want to make of it rather than any difference in performance.

Order of decreasing efficiency probably (though depending on library)

XOR
CRC
MD5
DES
3DES

If you want protect data from deliberate modification then you should use MD5 and encrypt the hash, there are many commercial and freeware libraries to assist you.  

If you just want to detect accidental corruption then XOR and CRC are accepted algorithms, but remember there is a chance (theoretically over 1:billion for CRC 32) that they can miss errors.

MD5 should be more reliable but is computationally more intensive.
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by:Moondancer
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Did this help you, arocio, so you may award expert(s) who helped you or is more needed here?  You have a number of old questions dating back to last year that remain open, awaiting your response as well.

Thank you for remaining active in your questions here and keeping experts who help you updated with progress.

Moondancer
Community Support Moderator @ Experts Exchange
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