Before I tell you about how to use MD5, I
would like to share one of my recent experience which made me start
using MD5 algorithm.
Recently I made some significant changes
and updates to my website and as obvious, I generated a complete backup
of the site on my server. I downloaded this backup onto my PC and
deleted the original one on the server. But after a few days something
went wrong and I wanted to restore the backup that I downloaded. When I
tried to restore the backup, I was shocked! The backup file that I used
to restore was corrupted.
That means, the backup file that I
downloaded onto my PC wasn’t exactly the one that was on my server. The
reason is that there occurred some data loss during the download
process. Yes, this data loss can happen often when a file is downloaded
from the Internet. The file can be corrupted due to any of the following
reasons:
-
Data loss during the download process, due to instability in the Internet connection/server.
-
The file can be tampered due to virus infections or
-
Due to Hacker attacks.
So, whenever you download any valuable
data from the Internet, it is completely necessary that you check the
integrity of the downloaded file. That is, you need to ensure that the
downloaded file is exactly the same as that of the original one. In this
scenario, the MD5 hash can become handy. All you have to do is generate
MD5 hash (or MD5 check-sum) for the intended file on your server.
After you download the file onto your
PC, again generate MD5 hash for the downloaded file. Compare these two
hashes and if they match, that means the file is downloaded perfectly
without any data loss.
A MD5 hash is nothing but a 32 digit hexadecimal number which can be something as follows:
A Sample MD5 Hash
e4d909c290d0fb1ca068ffaddf22cbd0
This hash is unique for every file
irrespective of it’s size and type. For example, two different
executable files (.exe files) with the same size will not have the same
MD5 hash even though they are of same type and size. So MD5 hash can be
used to uniquely identify a file.
How to use MD5 Hash to check the Integrity of Files?
Suppose you have a file called backup.tar on your server. Before you download, you need to generate MD5 hash for this file on your server. To do so use the following command:For UNIX:
md5sum backup.tar
When you hit ENTER you’ll see something as follows:
e4d909c290d0fb1ca068ffaddf22cbd0
This is the MD5 hash for the file backup.tar.
After you download this file onto your PC, you can cross check it’s
integrity by again re-generating MD5 hash for the downloaded file. If
both the hash matches then it means that the file is perfect. Otherwise
it means that the file is corrupt. To generate the MD5 hash for the
downloaded file on your Windows PC use the following freeware tool:
I hope you like this post. For further doubts and clarifications, please pass your comments. Cheers!
