Cryptographic hash function AND java

What is Cryptographic One Way Hash Function--

A cryptographic hash function is a deterministic procedure that takes plain text data and returns a fixed-size bit string, the hash value. The data to be encoded is often called the "message," and the hash value is called the message digest or simply digest. Every time on any platform a single algorithm will produce same message digest for same message.

Here the "one way" means that it's nearly impossible to derive the original text

(i.e.message) from the hash value i.e digest.

Using CHF for Checking Data Integrity --

By data integrity we generally mean the validity of the data. That is if the data

that we are seeing is the original data or some one has altered some or all of it. So here our need is not that, no one should see the data except the targeted audience, rather the need is no one should be able to alter the data and not being caught.

Using CHF we can achieve this, first calculate the hash value of the message and store it secretly, every time while accessing the message again calculate the hash value and check against the stored one to see if the original data is altered.

 Using CHF for Protecting Password --

When Sony's site was hacked, the hackers listed passwords of Sony users on web, which Sony had stored in plain text format according to the hackers, for which many cyber security experts criticized Sony. As passwords are essential tool for access protection.

CHF is a good candidate for protecting passwords by calculating a digest for the password and storing the digest instead of the plain text password for future references. And this works like this, while accepting password for the first time, use a hash function to calculate a digest and store the digest in the database. Next time when the user logs in, calculate the digest for the password given at that time using same hash function and compare the now calculated hash value/digest with the stored one. If the user have provided the same password then the two must be same else different.

Using MD5 in Java --

Massage Digest 5 is such a one way hash function algorithm. In below example we will see

how to use it in java.

Being a java developer we are blessed with a rich set of security features and inbuilt algorithm libraries. There are lots of libraries in java.security package and its sub packages

that implement hash functions.

In this code we will use MessageDigest class to create a digest for our supplied message and see the digested hash value as hex string .

package hashfunction;

import java.security.MessageDigest;

import java.security.NoSuchAlgorithmException;

public class MD5Demo {

public String createDigest(String pass){

String digest=null;

// Get bytes

byte[] bytePass2 = pass.getBytes();

// Run the MD5 algorithm.

MessageDigest alg = null;

try {

alg = MessageDigest.getInstance("MD5");

} catch (NoSuchAlgorithmException e) {

return null;

}

alg.reset();

alg.update(bytePass2);

byte[] hash = alg.digest();

// Extract the has values into a string.

StringBuilder sb = new StringBuilder();

for (int i = 0; i < hash.length; i++) {

String thehex = Integer.toHexString(0xFF & hash[i]);

// Java doesn't print leading zeros, so add one if needed.

if(thehex.length() == 1) sb.append('0');

sb.append(thehex);

}

digest = sb.toString();

return digest;

}

public static void main(String a[]){

System.out.println(new MD5Demo().createDigest("mindfire"));

}

}

Here the out put is 6876f31c02ad2082dd2f7c3fb0b90b90 for the input mindfire for any number of times on any platform.

However a small change like mindfier instead of mindfire will produce 883f744275a404b2a2d4c3ab7d1a2518, atotaly different result .

You can search the library for more functionalities, to make your program more secure.