Using MD5 Message Digest in Java

Cryptography Tutorials - Herong's Tutorial Examples

∟Using MD5 Message Digest in Java

This section provides a tutorial example on how to use MD5 message digest algorithm in Java. The JDK JCE package offers the MD5 algorithm through a generic message digest class, javax.security.MessageDigest.

Sun provides MD5 algorithm in Java under their JCE (Java Cryptography Extension) package, which is included in JDK 1.5 and newer versions.

Sun's implementation of MD5 can be accessed through a generic class called MessageDigest. Here are the main methods of MessageDigest class:

getInstance("MD5") - Returns a message digest object represents a specific implementation of MD5 algorithm from the default provider, Sun.
getProvider() - Returns the provider name of the current object.
update(bytes) - Updates the input message by appending a byte array at the end.
digest() - Performs MD5 algorithm on the current input message and returns the message digest as a byte array. This method also resets the input message to an empty byte string.
reset() - Resets the input message to an empty byte string.

Here is a sample Java program to show you how to use the MessageDigest class to perform some tests on MD5 algorithms.

/* JceMd5Test.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
import java.security.*;
class JceMd5Test {
   public static void main(String[] a) {
      try {
         MessageDigest md = MessageDigest.getInstance("MD5");
         System.out.println("Message digest object info: ");
         System.out.println("   Algorithm = "+md.getAlgorithm());
         System.out.println("   Provider = "+md.getProvider());
         System.out.println("   toString = "+md.toString());

         String input = "";
         md.update(input.getBytes()); 
         byte[] output = md.digest();
         System.out.println();
         System.out.println("MD5(\""+input+"\") =");
         System.out.println("   "+bytesToHex(output));

         input = "abc";
         md.update(input.getBytes()); 
         output = md.digest();
         System.out.println();
         System.out.println("MD5(\""+input+"\") =");
         System.out.println("   "+bytesToHex(output));

         input = "abcdefghijklmnopqrstuvwxyz";
         md.update(input.getBytes()); 
         output = md.digest();
         System.out.println();
         System.out.println("MD5(\""+input+"\") =");
         System.out.println("   "+bytesToHex(output));
         
      } catch (Exception e) {
         System.out.println("Exception: "+e);
      }
   }
   public static String bytesToHex(byte[] b) {
      char hexDigit[] = {'0', '1', '2', '3', '4', '5', '6', '7',
                         '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
      StringBuffer buf = new StringBuffer();
      for (int j=0; j<b.length; j++) {
         buf.append(hexDigit[(b[j] >> 4) & 0x0f]);
         buf.append(hexDigit[b[j] & 0x0f]);
      }
      return buf.toString();
   }
}

If you run this sample program, you should get the following output:

herong> javac JceMd5Test.java

herong> java JceMd5Test

Message digest object info:
   Algorithm = MD5
   Provider = SUN version 12
   toString = MD5 Message Digest from SUN, <initialized>

MD5("") =
   D41D8CD98F00B204E9800998ECF8427E

MD5("abc") =
   900150983CD24FB0D6963F7D28E17F72

MD5("abcdefghijklmnopqrstuvwxyz") =
   C3FCD3D76192E4007DFB496CCA67E13B