What is MD5 Hash and How to Use it?

This is interesting cryptographic algorithm called MD5 (Message-Digest algorithm 5). This algorithm is mainly used to perform file integrity checks under most circumstances and to tell you about how to make use of this algorithm in your daily life
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
http://www.md5summer.org/download.html
http://en.wikipedia.org/wiki/Cryptography