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question about md5sums

I noticed that if I open K3B to burn a downloaded iso, it seems to have the md5sum (displayed in the information box of the K3B burning window) even though I didn't download the md5sum file with the iso. If it somehow got the md5sum without my downloading the md5sum file, why would I have needed to download it anyway? Although I understand what md5sums do, I don't understand this.

Quote:

Originally Posted by newbiesforever (Post 3806057)

If it somehow got the md5sum without my downloading the md5sum file, why would I have needed to download it anyway? Although I understand what md5sums do, I don't understand this.

The md5sum is computed from the contents of the file.

The purpose of the md5sum is to verify that there were no errors in downloading the file. If you had an error in downloading the file, the ms5sum computed from the contents would not match the md5sum you could download separately.

So the md5sum displayed by K3B is the one computed from the available contents. If the contents were wrong, the displayed md5sum would be wrong. The display of the md5sum does not mean it is known to be the original correct md5sum.

You can also run the md5sum command manually if you like: run it on the file k3b is writing. Then you will see for yourself how it came up with the number.