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...difference between a message authentication...

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Question by PiGHead
Submitted on 3/6/2004
Related FAQ: Cryptography FAQ (01/10: Overview)
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What is the difference between a message authentication code(MAC) and a one-way hash function?


Answer by koti
Submitted on 3/30/2004
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the difference between a message authentication code and one way hash functıonts more secure.

 

Answer by Marcos Juarez
Submitted on 6/27/2004
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The difference between a one-way hash and a MAC (Message authentication code), is that the hash verifies the uniqueness of a message or file.  The MAC is usually an encrypted hash, also used to verify the uniqueness of a message, but which only can be verified if you know the secret key.

For example, say you have a list of the MD5 hashes of all your system files.  If you verify the MD5 values of the files periodically with this list, you could see which files have been changed or updated, by a virus, for instance.  However, if a virus comes in your system, and replaces a system file, it could also replace the MD5 value in your list with the new one, and you wouldn't know this happened.

If you had a list of MACs, however, the virus could replace your system file, but it has no way of replacing the hash, since it doesn't have the key to decrypt it.

 

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