The purpose of a checksum (1 Viewer)

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I havent looked this up and ive never performed a checksum operation on a piece of software ive downloaded but i would assume the purpose is to verify that the return value matches that provided by the creator on the website or the mirror? How does one go about running a check like this? Only time ive ever hashed anything was in PHP via SHA1 and MD5, both of which are built in functions.
 

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Check sums are normally used as a quick "Did everything arrive" check on a packet or file. Do a bitwise AND through all bites in a packet and compare your result to the Checksum bit. If they match, you can be reasonably certain you have no corruption.

Checksums for files are similar but also often include the total byte count for a file. If you have to many/to few bites, you have a problem. If the checksum comes out off you have a problem.

These are also sometimes used to identify if a file has been changed for malicious reasons.
 

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