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There are two discs that we have that have all the same files. However, using a new method for burning the discs, the second disc had modified file dates of 5/30/2018 while the original disc has dates of 2013.

The hash value of each CD is identical.

I tried to recreate this by making a Microsoft Word document that had the word 'blue' in size 12 Times New Roman. First I had my name as the author and hashed the file. I added an other through Windows Explorer in the details tab of the properties menu. The hash value of each file, though stored in the same folder with the same content differed between the two files.

Is there an easy explanation for what two cds with files having different modification dates be identical?

Thanks in advance.

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    $\begingroup$ Change dates are part of the filesystem metadata and not of the file content itself, and thus don't get considered when hashing the file content. $\endgroup$ – CodesInChaos Jun 1 '18 at 15:44
  • $\begingroup$ Thanks for the response, that's what I was hoping but testing with the word file threw me for a loop. $\endgroup$ – J. Doe Jun 1 '18 at 17:01
  • $\begingroup$ "The hash value of each CD is identical" is likely erroneous. The hash value of two files with the same pathname on the two CDs can be identical, OK. $\endgroup$ – fgrieu Jun 1 '18 at 17:03
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The hash value of each file, though stored in the same folder with the same content differed between the two files.

That is because MS Word encodes things like who last changed the file in its actual file instead of just in the filesystem metadata. Thus this change indeed affects the hash.

Is there an easy explanation for what two cds with files having different modification dates be identical?

CodesInChaos provided the answer in the comments:

Change dates are part of the filesystem metadata and not of the file content itself, and thus don't get considered when hashing the file content.

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  • $\begingroup$ Thanks for the response, I will test with another file type. That's what I was hoping to hear at least. $\endgroup$ – J. Doe Jun 1 '18 at 17:03

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