If you are really serious about your online privacy and PC security, you will know that Hash functions are important tools to validate the authenticity and integrity of a file. Say, when you download a file from Internet, you never know, whether the source file and the file which you have actually received, are exactly same. There are chances that some malware has been attached to it.
Hash functions are a means to validate the authenticity of the downloaded files from the source.
What is a HASH Function:
A cryptographic hash function is a deterministic procedure that takes an arbitrary block of data and returns a fixed-sizebit string, the (cryptographic) hash value, such that an accidental or intentional change to the data will change the hash value. The data to be encoded is often called the “message”, and the hash value is sometimes called the message digestor simply digest.
The ideal cryptographic hash function has four main or significant properties:
- it is easy to compute the hash value for any given message,
- it is infeasible to find a message that has a given hash,
- it is infeasible to modify a message without hash being changed,
- it is infeasible to find two different messages with the same hash.
Cryptographic hash functions have many information security applications, notably in digital signatures, message authentication codes (MACs), and other forms of authentication. They can also be used as ordinary hash functions, to index data in hash tables, for fingerprinting, to detect duplicate data or uniquely identify files, and as checksums to detect accidental data corruption. Indeed, in information security contexts, cryptographic hash values are sometimes called (digital) fingerprints, checksums, or just hash values, even though all these terms stand for functions with rather different properties and purposes.
How to calculate Hash Function of a file
Here are two tools, which are freeware and easy to use.
HashTab: HashTab provides OS extensions to calculate file hashes. HashTab supports many hash algorithms such as MD5, SHA1, SHA2, RipeMD, HAVAL and Whirlpool. Hashtab is supported as a Windows shell extension and a Mac Finder plugin. HashTab provides an easy way to verify file integrity and authenticity.
Once you have installed HashTab, just right click on any file. On Windows, select properties and you will see a new “File Hashes” tab. On Mac select “File Hashes” (on 10.5 the “File Hashes” menu item will be found under the “More” submenu). This is will start HashTab providing more or less the same view that you see on Windows. This File Hashes window displays all the hashes for the file. You can customize which hashes are calculated and displayed. You can hash other files for comparison. You can also paste in hash text so you don’t go cross-eyed trying to compare MD5 hashes.
HashMyFiles: HashMyFiles is small utility that allows you to calculate the MD5 and SHA1 hashes of one or more files in your system. You can easily copy the MD5/SHA1 hashes list into the clipboard, or save them into text/html/xml file.
HashMyFiles can also be launched from the context menu of Windows Explorer, and display the MD5/SHA1 hashes of the selected file or folder. HashMyFiles doesn’t require any installation process or additional DLL files