Hash of imz files are not consistent

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drm200
Posts: 1
Joined: Thu May 14, 2015 9:16 am

Hash of imz files are not consistent

Post by drm200 »

I have a 16 gb USB that is bootable and that I back-up in device mode using USB Image Tool ver 1.70.

If I do the backup in img format ... and then backup the same USB a second time.... the resulting two files are found to be identical when I use Nirsofts hash utility to compare the MD5 hash of the two img files.

Now if I do the backup in imz format twice and then use the the Nirsoft utility to evaluate the MD5 hash of each imz file, I can see that the resulting MD5 hash is different for the two imz files.

Now if I use 7zip to unzip the two imz files ... and then use the Nirsoft utilty to evaluate the MD5 hash of the unzipped img files ... the md5 hash is found to be the same as the original img files ... So I guess everything is OK as the original image is identical to the unzipped imz image .... But it is very confusing to see the imz files result in different MD5 hash results.

I'm just posting this in case other users notice that the MD5 hash of imz files are different (when they may have expected them to be the same). In order to compare the imz files you need to first unzip the img and then compare the MD5 hash of the two img files.
Alex
Site Admin
Posts: 267
Joined: Fri Jul 29, 2011 11:59 pm

Re: Hash of imz files are not consistent

Post by Alex »

The imz files contain more information than just the plain data. I assume the imz image files will be slightly different themselves. That's because the file time of the containing raw image will be different. As a result the MD5 hashes of two imz images with the same image created at different times will always be different. For that reasons the MD5 created by USB Image Tool are done for the uncompressed image.
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