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

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:

When you hit ENTER you’ll see something as follows

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!

What exactly is Secure Communication ?

Suppose there exists two communication parties A (client) and B (server).

Working of HTTP

When A sends a message to B, the message is sent as a plain text in an unencrypted manner. This is acceptable in normal situations where the messages exchanged are not confidential. But imagine a situation where A sends a PASSWORD to B. In this case, the password is also sent as a plain text. This has a serious security problem because, if an intruder (hacker) can gain unauthorised access to the ongoing communication between A and B , he can see the PASSWORDS since they remain unencrypted. This scenario is illustrated using the following figure

Now lets see the working of HTTPS

When A sends a PASSWORD (say “mypass“) to B, the message is sent in an encrypted format. The encrypted message is decrypted on B‘s side. So even if the Hacker gains an unauthorised access to the ongoing communication between A and B he gets only the encrypted password (“xz54p6kd“) and not the original password. This is shown below

How is HTTPS implemented ?

HTTPS is implemented using Secure Sockets Layer (SSL). A website can implement HTTPS by purchasing an SSL Certificate. Secure Sockets Layer (SSL) technology protects a Web site and makes it easy for the Web site visitors to trust it. It has the following uses

1. An SSL Certificate enables encryption of sensitive information during online transactions.
2. Each SSL Certificate contains unique, authenticated information about the certificate owner.
3. A Certificate Authority verifies the identity of the certificate owner when it is issued.

How Encryption Works ?

Each SSL Certificate consists of a Public key and a Private key. The public key is used to encrypt the information and the private key is used to decrypt it. When your browser connects to a secure domain, the server sends a Public key to the browser to perform the encryption. The public key is made available to every one but the private key(used for decryption) is kept secret. So during a secure communication, the browser encrypts the message using the public key and sends it to the server. The message is decrypted on the server side using the Private key(Secret key).

How to identify a Secure Connection ?
In Internet Explorer, you will see a lock icon in the Security Status bar. The Security Status bar is located on the right side of the Address bar. You can click the lock to view the identity of the website.

In high-security browsers, the authenticated organization name is prominently displayed and the address bar turns GREEN when an Extended Validation SSL Certificate is detected. If the information does not match or the certificate has expired, the browser displays an error message or warning and the status bar may turn RED.

So the bottom line is, whenever you perform an online transaction such as Credit card payment, Bank login or Email login always ensure that you have a secure communication. A secure communication is a must in these situations. Otherwise there are chances of Phishing using a Fake login Page.

I Hope this helps. Please pass your comments.