Cryptography is conversion of plain readable text into unreadable form. In cryptography first the data is converted into cipher text (that is encryption) and then the cipher text is converted back into readable form (that is decryption). Cryptography basically works on the concept of encryption and decryption. Encryption and decryption should not be confused with encoding and decoding, in which data is converted from one form to another but is not deliberately altered so as to conceal its content. Encryption is achieved through the algorithms. These algorithms are works with logic, mathematic calculations and its complexities.
Hash Function is most important function in Cryptography. A hash means a 1 to 1 relationship between data. This is a common data type in languages, although sometimes it’s called a dictionary. A hash algorithm is a way to take an input and always have the same output, otherwise known as a 1 to 1 function. An ideal hash function is when this same process always yields a unique output. So you can tell someone, here is a file, and here is its md5 hash. If the file has been corrupted during then the md5 hash will be a different value.
In practice, a hash function will always produce a value of the same size, for instance md5 () is will always return 128bits no matter the size of the input. This makes a 1 to 1 relationship impossible. A cryptographic hash function takes extra precautions in making it difficult to produce 2 different inputs with the same output, this is called a collision. It also makes it difficult to reverse the function. Hash functions are used for password storage because if an attacker where to obtain the password's hash then it forces the attacker to break the hash before he can use it to login. To break hashes, attackers will take a word list or an English dictionary and find all of the corresponding hash values and then iterate though the list for each password looking for a match.
md5 (), sha0 and sha1 () are all vulnerable to a hash collision attacks and should never be used for anything security related. Instead any member of the sha-2 family, such as sha-256 should be used.
To calculate Hash Value, we will use Hash Calculator. Install Hash Calculator from --> http://www.slavasoft.com/hashcalc/
Hash function plays major role in hacking/forensic world because it helps us to know whether a particular file has changed or not. You can also calculate hash value of your computer and know if anyone has made any kind of changes.
To calculate hash value open Hash Calculator.
Now browse the file of which you want to calculate the hash value. And click on Calculate.
After clicking on calculate it will give too hash values using four different hashing algorithms i.e MD5, SHA1, RIPEMD160, CRC32. You can check other boxes too if you want to use those algorithms to calculate hash value.
This way Hash calculator helps us to know the hash value. Now if there are any changes made in this file, the hash value will change too.
Once I calculated the hash value above i made some changes in the file and calculated the hash value again with the same method and as a result the hash value was changed.
Now, we have two hash values. Let us compare both of these values of MD5. The value of first file is 1110808875326e25dl93e4ee096afaf1 and the value of other file is fb9d53883f302d78c978a583e8a85.
Seeing these two values of MD5 of the same file we can conclude that some changes are made. Because even slightest difference will change the hash value.
But now the main question is how to detect this change because a file can be of 1TB too. Also imagine that you are sending a harddisk full of important documents to someone and there is a huge possibility that someone can bribe the sender and make changes in your documents. So how can you detect these changes?
The answer is very simple --> Compare it! This tool helps us achieve our goal which is to detect the change.
Download Compare it! From -->http://www.grigsoft.com/wincmp3.htm
Open Compare it!
Click file and a drop menu will appear. Select compare files option.
A Dialogue box will open which will ask you to choose the files that you want to compare. Click on Browse button and select your file. And click on Open.
It will show you the changes by highlighting them with green color and the red color will tell the exact change as shown below:
So, in such way you can protect your sensitive data and detect the crime done too.