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md5 and files

md5

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4 replies to this topic

#1 baldgrapeape

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Posted 20 October 2010 - 04:05 PM

Hi,

If someone were writing a program to calculate an md5 hash of a file, (for this purpose let's say language doesn't matter) I wonder a few things which maybe you can help me with please.

If you have an audio file 2 minutes in length and have hashed it, would adding :05 of dead air (no noise, no hiss, nothing but dead air) would that change the hash value?

If you change the ID tag of the file would that change the hash?

What would the code be taking into account in order to render a change to a different md5.

Thanks a lot.

Ape.
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#2 WingedPanther73

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Posted 20 October 2010 - 04:27 PM

Yes.
Yes.
The file is different.
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#3 Alexander

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Posted 20 October 2010 - 05:28 PM

A single binary bit changed will significantly modify the resulting MD5 hash, you can follow the source of the MD5 algorithm and see the significant steps it takes to do so.
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#4 baldgrapeape

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Posted 21 October 2010 - 11:45 AM

Thanks for the replies.

I guess that makes sense that the ID is part of the actual file so the MD5 would change then.
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#5 zoranh

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Posted 21 October 2010 - 02:14 PM

But if you are implementing hash algorithm on your own, then you can decide to skip part of the file, knowing the file format. For example, if you want ID tag to be modifiable without affecting hash value, then skip bytes containing ID when calculating hash.
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