In cryptography, MD5 (Message Digest version 5) and SHA (Secure Hash Algorithm) are two well-known message digest algorithms. They are also referred as cryptographic hash functions, which take arbitrary-sized data as input (message) and produce a fixed-length hash value. One of the most important properties of hash functions is, it’s infeasible to generate a message that has a given hash (secure one-way). Hash functions are frequently used to check data integrity such as checking integrity of a downloaded file against its publicly-known hash value. Another common usage is to encrypt user’s password in database.

The Java platform provides two implementation of hashing functions: MD5 (produces 128-bit hash value), SHA-1 (160-bit) and SHA-2 (256-bit). This tutorial demonstrates how to generate MD5 and SHA hash values from String or file using Java.

Here are general steps to generate a hash value from an input (message):

• First approach (suitable for small-sized message):

  // algorithm can be "MD5", "SHA-1", "SHA-256"
  MessageDigest digest = MessageDigest.getInstance(algorithm);
  
  byte[] inputBytes = // get bytes array from message
  
  byte[] hashBytes = digest.digest(inputBytes);
  
  // convert hash bytes to string (usually in hexadecimal form)

• Second approach (suitable for large-size message, i.e. large file):

  MessageDigest digest = MessageDigest.getInstance(algorithm);
  
  byte[] inputBytes = // get bytes array from message
  
  digest.update(inputBytes);
  
  byte[] hashedBytes = digest.digest();
  
  // convert hash bytes to string (usually in hexadecimal form)

   

Now, let’s see some examples in details.

 

1. Generating Hash from String

The following method takes a message and algorithm name as inputs and returns hexadecimal form of the calculated hash value:

private static String hashString(String message, String algorithm)
		throws HashGenerationException {

	try {
		MessageDigest digest = MessageDigest.getInstance(algorithm);
		byte[] hashedBytes = digest.digest(message.getBytes("UTF-8"));

		return convertByteArrayToHexString(hashedBytes);
	} catch (NoSuchAlgorithmException | UnsupportedEncodingException ex) {
		throw new HashGenerationException(
				"Could not generate hash from String", ex);
	}
}

The HashGenerationException is a custom exception (you can find this class in the attachment). The convertByteArrayToHexString() method is implemented as follows:

private static String convertByteArrayToHexString(byte[] arrayBytes) {
	StringBuffer stringBuffer = new StringBuffer();
	for (int i = 0; i < arrayBytes.length; i++) {
		stringBuffer.append(Integer.toString((arrayBytes[i] & 0xff) + 0x100, 16)
				.substring(1));
	}
	return stringBuffer.toString();
}

The hashString() is a general method. Here are four public utility methods that are specific to each algorithm (MD5, SHA-1 and SHA-256):

public static String generateMD5(String message) throws HashGenerationException {
	return hashString(message, "MD5");
}

public static String generateSHA1(String message) throws HashGenerationException {
	return hashString(message, "SHA-1");
}

public static String generateSHA256(String message) throws HashGenerationException {
	return hashString(message, "SHA-256");
}

Hence we have the following utility class:

package net.codejava.security;

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * Hash functions utility class.
 * @author www.codejava.net
 *
 */
public class HashGeneratorUtils {
	private HashGeneratorUtils() {

	}

	public static String generateMD5(String message) throws HashGenerationException {
		return hashString(message, "MD5");
	}

	public static String generateSHA1(String message) throws HashGenerationException {
		return hashString(message, "SHA-1");
	}

	public static String generateSHA256(String message) throws HashGenerationException {
		return hashString(message, "SHA-256");
	}

	private static String hashString(String message, String algorithm)
			throws HashGenerationException {

		try {
			MessageDigest digest = MessageDigest.getInstance(algorithm);
			byte[] hashedBytes = digest.digest(message.getBytes("UTF-8"));

			return convertByteArrayToHexString(hashedBytes);
		} catch (NoSuchAlgorithmException | UnsupportedEncodingException ex) {
			throw new HashGenerationException(
					"Could not generate hash from String", ex);
		}
	}

	private static String convertByteArrayToHexString(byte[] arrayBytes) {
		StringBuffer stringBuffer = new StringBuffer();
		for (int i = 0; i < arrayBytes.length; i++) {
			stringBuffer.append(Integer.toString((arrayBytes[i] & 0xff) + 0x100, 16)
					.substring(1));
		}
		return stringBuffer.toString();
	}
}

Here’s a test program:

package net.codejava.security;

/**
 * Test generating hash values from String.
 * @author www.codejava.net
 *
 */
public class StringHashGeneratorExample {

	public static void main(String[] args) {
		try {
			String inputString = args[0];
			System.out.println("Input String: " + inputString);

			String md5Hash = HashGeneratorUtils.generateMD5(inputString);
			System.out.println("MD5 Hash: " + md5Hash);

			String sha1Hash = HashGeneratorUtils.generateSHA1(inputString);
			System.out.println("SHA-1 Hash: " + sha1Hash);

			String sha256Hash = HashGeneratorUtils.generateSHA256(inputString);
			System.out.println("SHA-256 Hash: " + sha256Hash);
		} catch (HashGenerationException ex) {
			ex.printStackTrace();
		}
	}

}

If the input message is “admin” the test program produces the following output:

Input String: admin
MD5 Hash: 21232f297a57a5a743894a0e4a801fc3
SHA-1 Hash: d033e22ae348aeb5660fc2140aec35850c4da997
SHA-256 Hash: 8c6976e5b5410415bde908bd4dee15dfb167a9c873fc4bb8a81f6f2ab448a918

 

2. Generating Hash from File

To calculate hash value of a large file effectively, it’s recommended to repeatedly put a chunk of bytes to the message digest, until reaching end of file. Here’s such method:

private static String hashFile(File file, String algorithm)
		throws HashGenerationException {
	try (FileInputStream inputStream = new FileInputStream(file)) {
		MessageDigest digest = MessageDigest.getInstance(algorithm);

		byte[] bytesBuffer = new byte[1024];
		int bytesRead = -1;

		while ((bytesRead = inputStream.read(bytesBuffer)) != -1) {
			digest.update(bytesBuffer, 0, bytesRead);
		}

		byte[] hashedBytes = digest.digest();

		return convertByteArrayToHexString(hashedBytes);
	} catch (NoSuchAlgorithmException | IOException ex) {
		throw new HashGenerationException(
				"Could not generate hash from file", ex);
	}
}

Here are four public methods that are specific to each algorithm:

public static String generateMD5(File file) throws HashGenerationException {
	return hashFile(file, "MD5");
}

public static String generateSHA1(File file) throws HashGenerationException {
	return hashFile(file, "SHA-1");
}

public static String generateSHA256(File file) throws HashGenerationException {
	return hashFile(file, "SHA-256");
}

And here’s a test program:

package net.codejava.security;

import java.io.File;

/**
 * Test generating hash values from File.
 * @author www.codejava.net
 *
 */
public class FileHashGeneratorExample {

	public static void main(String[] args) {
		try {
			String filePath = args[0];
			System.out.println("File Path: " + filePath);
			File file = new File(filePath);
			
			String md5Hash = HashGeneratorUtils.generateMD5(file);
			System.out.println("MD5 Hash: " + md5Hash);
			
			String sha1Hash = HashGeneratorUtils.generateSHA1(file);
			System.out.println("SHA-1 Hash: " + sha1Hash);

			String sha256Hash = HashGeneratorUtils.generateSHA256(file);
			System.out.println("SHA-256 Hash: " + sha256Hash);			

		} catch (HashGenerationException ex) {
			ex.printStackTrace();
		}
	}

}

Example output:

File Path: D:\Java\PDFViewer\JPedalPDFViewer.zip
MD5 Hash: 56a86f56a18b73353e5f0afa7b142ed1
SHA-1 Hash: dc55bd7e84c4787242499ec068fa145bcca01937
SHA-256 Hash: 093059d79d009662a0a7f70c74cec934a73c1becc8ac813cdcc4995f2aeb882c

 

NOTES:

MD5 was found insecure, so it’s recommended to use SHA-256 instead for better security.

 

References:

• MD5 on Wikipedia
• Secure Hash Algorithm on Wikipedia
• Cryptographic hash function on Wikipedia
• Class MessageDigest Javadoc

 

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