MessageDigest in Java

MessageDigest is the returned value of the hash function, which is also known as has values. Hash functions are mostly used in each and every information security application. Hash functions are used for converting numerical values into compressed numerical values. For Hash functions, the length of the user-given input can be arbitrary, but the length of the output is always of fixed length.

The java.security package provides a class, i.e., MessageDigest, that supports algorithms such as SHA-1, SHA 256, and MD5 etc., for converting a message of arbitrary length to a message digest.

In order to convert a message into MessageDigest, we use the following steps:

1. In the first step, we will create an instance of the MessageDigest by using the getInstance() method of the MessageDigest The getInstance() method accepts a parameter, i.e., algo, which defines the algorithm to be used.

The getInstance() method returns a MessageDigest object implementing the specified algorithm.

2. In the next step, we will pass the message to the created MessageDigest instance. For passing the value, we use the update() method of the MessageDigest class. The update() method accepts data in the form of the byte array.

3. In the next step, we will use the digest() method of the MessageDigest class to generate the message digest. The digest() method is responsible for computing the hash function on the current object. The digest() method returns the message digest in the form of the byte array.

Let's implement the code for understanding how we can use the MessageDigest class by using the above steps:

MessageDigestExample.java

// import required classes and package if any
import java.security.MessageDigest;
import java.util.Scanner;
// create class MessageDigestExample to understand the use of MessageDigest class
public class MessageDigestExample {
	// main() method start
	public static void main(String args[]) throws Exception{
		// create an instance of Scanner class
		Scanner sc = new Scanner(System.in);
		System.out.println("Enter the message of any arbitrary length:");
		String msg = sc.nextLine();
		// close Scanner class
		sc.close();
		//create an instance of the MessageDigest by using the getInstance() method with the SHA-256 algorithm
		MessageDigest obj = MessageDigest.getInstance("SHA-256");
	//use update() method for passing data to the created MessageDigest Object
		obj.update(msg.getBytes());
		//use the digest() method for computing the message digest
		byte[] byteArray = obj.digest();
		System.out.println(byteArray);  
		//convert the byte array in to Hex String format
		StringBuffer hexData = new StringBuffer();
		for (int i = 0; i < byteArray.length; i++) {
			hexData.append(Integer.toHexString(0xFF & byteArray[i]));
		}
		System.out.println("Data in Hex format : " + hexData.toString());     
	}
}

Output:

The getInstance() method of the MessageDigest class can throw the NoSuchAlgorithmException when no provider supports the message digest spi application for the particular algorithm.

MessageDigestExceptionExample.java

//import required classes and package, if any
import java.security.MessageDigest;
import java.util.Scanner;
//create class MessageDigestExceptionExample to understand how getInstance() throw an exception 
public class MessageDigestExceptionExample {
	// main() method start
	public static void main(String args[]){
		// create an instance of Scanner class
		Scanner sc = new Scanner(System.in);
		System.out.println("Enter the message of any arbitrary length:");
		String msg = sc.nextLine();
		// close Scanner class
		sc.close();
		try {
			//create an instance of the MessageDigest by using the getInstance() method with the JTP algorithm
			MessageDigest obj = MessageDigest.getInstance("JTP");	//throw an error
//use update() method for passing data to the created MessageDigest Object
			obj.update(msg.getBytes());
			//use the digest() method for computing the message digest
			byte[] byteArray = obj.digest();
			System.out.println(byteArray);  
			//convert the byte array in to Hex String format
			StringBuffer hexData = new StringBuffer();
			for (int i = 0; i < byteArray.length; i++) {
			hexData.append(Integer.toHexString(0xFF & byteArray[i]));
			}
			System.out.println("Data in Hex format : " + hexData.toString()); 
		}catch(Exception e) {
			System.out.println(e);
		}    
	}
}

Output: