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One day a friend told me I could check the "name" or "author" of whatever file I downloaded from someone else.

So basically, if my name is Joe and I create a text file and upload it and you download it, you can check somewhere "Joe"? Dunno, in properties or something?

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3 Answers 3

Metatags or such are unreliable and can be changed easily. Its also dependent on format - word would have it, but text may not.

If you really need to be certain a file is genuine, get the creator to make an MD5 sum and compare the md5 sum of your file to that of the creator.

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Could you please elaborate more on these interesting metatags? Thank you. –  Noburishta Mar 24 '11 at 1:25
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If it was that easy, why bother with GPG? –  Florenz Kley Mar 24 '11 at 1:28
    
GPG ensures that the sender is what he says he is. checksums ensure the file is what it should be. They have very different roles. –  Journeyman Geek Mar 24 '11 at 2:04
    
@norburshta : en.wikipedia.org/wiki/Metadata that would be a start. –  Journeyman Geek Mar 24 '11 at 2:05

A MD5 checksum would be the most reliable way to ensure the file hasen't been modified from author to the receiver.

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If I could add further to these two useful answers (and on the topic of "GPG"). If you need to be utterly certain of who sent the file, as opposed to whether the file has changed in transit, you need to use some implementation of digital signatures - see http://en.wikipedia.org/wiki/Digital_signature

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