What is MD5 Hash and How to Use it?

Submitted by Srikanth on Tuesday, 19 January 201018 Comments

In this post I will explain you about one of my favorite and interesting cryptographic algorithm called MD5 (Message-Digest algorithm 5). This algorithm is mainly used to perform file integrity checks under most circumstances. Here I will not jump into the technical aspects of this algorithm, rather will tell you about how to make use of this algorithm in your daily life. 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 occured 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 it matches then it means that the file is downloaded perfectly without any data loss.

A MD5 hash is nothing but a 32 digit hexadicimal 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. That means two .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

MD5 Summer (Click on the link to download)

I hope you like this post. For further doubts and clarifications please pass your comments. Cheers!

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18 Comments »

David said:

Hello…you Really Rock ! Can i ask u 1 q? do u know how to make a good template for a blog? please reply

- 19 January 2010 at 6:47 PM

Karan Kapoor said:

I am great fan of urs Srikanth

- 20 January 2010 at 7:13 PM

funcky said:

Is that “md5sum” inbuilt command ?
Or have to install any extra packages?
And another thing is that will it work on linux?

- 20 January 2010 at 9:32 PM

Srikanth (author) said:

@ funcky

MD5SUM is inbuilt on all UNIX systems. However on Windows your need to install the package. The download link is given in the post itself.

- 21 January 2010 at 12:23 PM

Abhijeet said:

Hi!Thanks for giving lot of knowledge

- 31 January 2010 at 10:53 AM

Abhijeet said:

Thanks Srikanth for such a wonderful tip…but the download link is not working…

- 14 February 2010 at 1:48 PM

ankit said:

hi i really like your article

- 3 April 2010 at 5:26 PM

AryaN said:

hey dude…bt hw 2 decrypt d encryptd code….???

- 16 April 2010 at 11:33 PM

xDjura said:

Thanks alot ur hacks are great!

- 17 April 2010 at 2:24 PM

SNS said:

Thz for the post.;…:)

- 19 April 2010 at 6:22 PM

Karthick said:

Very nice information

- 3 May 2010 at 2:13 PM

Faizal said:

Hi sri, i have one doubt , can we convert MD5 hash to a real string(text) , that should be the same used to convert MD5

- 14 May 2010 at 9:35 PM

Srikanth (author) said:

@ Faizal

MD5 hash is reversible only when you know the method and the key used for encryption. Often this is kept secret and hence it’s not possible to reverse it back in most cases. If you know then you can decrypt (reverse) it back.

- 17 May 2010 at 2:30 PM

rajul said:

you rocks dude i have visited many hacking sites bt this is best awesome but i have problem in compiling file it tels so many errors

- 29 May 2010 at 8:32 AM

aditya snehil said:

how to decrypt md5 hash….

- 31 May 2010 at 1:11 PM

Themsay said:

Sir ur posts has been a guide and I love it so much.
I too still ‘ve a problem on compiling file to exe? pls, where u said cd command has been my problem. I need ur help thanks.

- 18 June 2010 at 6:35 PM

MD5 Hash said:

Hi Srikanth.
Very good explanation. Just thought you’d like to know I’ve built a web tool for performing MD5 sums. You can use it here: http://www.md5hasher.net

Regards

- 24 June 2010 at 1:02 AM

nasir said:

It is really awsome post about md5 encryption security.Thanks a lot for this post.

- 13 July 2010 at 1:05 PM