MD5 (Message-Digest algorithm 5) is a widely used cryptographic hash function with a 128-bit hash value. Specified in RFC 1321, MD5 is one in a series of message digest algorithms designed by Professor Ronald Rivest of MIT (Rivest, 1994). Today MD5 has been employed in a wide variety of security applications, and is also worldwide used to check the integrity of files.

MD5 is perfect fine solution for security thinking. As a Java developer, we usually take over or coding to md5 encryption, the md5 encryption is very complicated and not easy to understand and implement. The good news is that the Java standard edition has MD5 support built in. according by the specification of class MessageDigest, it supports the functionality of a message digest algorithm, such as MD5 or SHA. and it is defined and included in java.security package. first you need some string manipulation to turn the plain text into byte array. This is easy that just use method getBytes() of class string. the digest is then updated from the bytes from the byte array and a hash computation is conducted upon them.

1. Simple example Hash String with MD5 algorithm

Here is a simple Java MD5 example. it passes into a string and returns the MD5 encryption value by calling MessageDigest.

import java.io.FileInputStream;
import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MD5 {
    public static String getMD5(String input) {
        try {
            MessageDigest md = MessageDigest.getInstance("MD5");
            byte[] messageDigest = md.digest(input.getBytes());
            BigInteger number = new BigInteger(1, messageDigest);
            String hashtext = number.toString(16);
            // Now we need to zero pad it if you actually want the full 32 chars.
            while (hashtext.length() < 32) {
                hashtext = "0" + hashtext;
            }
            return hashtext;
        }
        catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        }
    }

    public static void main(String[] args) throws NoSuchAlgorithmException {
        System.out.println(getMD5("Javarmi.com"));
    }
}

Java MD5 example Output:
0127f712fc008f857e77a2f3f179c710

2. Another way Hashing String with MD5 algorithm

Another Java MD5 encryption example, its same with the first way that accepts string and returns MD5 encryption value.

import java.io.FileInputStream;
import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MD5 {
    public static String getMD5(String input) {
        byte[] source;
        try {
            //Get byte according by specified coding.
            source = input.getBytes("UTF-8");
        } catch (UnsupportedEncodingException e) {
            source = input.getBytes();
        }
        String result = null;
        char hexDigits[] = {'0', '1', '2', '3', '4', '5', '6', '7',
                '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
        try {
            MessageDigest md = MessageDigest.getInstance("MD5");
            md.update(source);
            //The result should be one 128 integer
            byte temp[] = md.digest();
            char str[] = new char[16 * 2];
            int k = 0;
            for (int i = 0; i < 16; i++) {
                byte byte0 = temp[i];
                str[k++] = hexDigits[byte0 >>> 4 & 0xf];
                str[k++] = hexDigits[byte0 & 0xf];
            }
            result = new String(str);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result;
    }

    public static void main(String[] args) throws NoSuchAlgorithmException {
        System.out.println(getMD5("Javarmi.com"));
    }
}

Java MD5 example Output
0127f712fc008f857e77a2f3f179c710

3. File checksum with Java MD5

MD5 algorithm is also widely used for file checksum to ensure that files are not modified by attacker, We have an example that use Java MD5 hashing algorithm to generate a checksum for file “c:\\apache\\cxf.jar”. please check whether the print-out value  matches the original MD5 value which was released by Jar Publisher.

    public static void main(String[] args) throws Exception {
        MessageDigest md = MessageDigest.getInstance("MD5");
        FileInputStream fis = new FileInputStream("c:\\apache\\cxf.jar");

        byte[] dataBytes = new byte[1024];

        int nread = 0;
        while ((nread = fis.read(dataBytes)) != -1) {
            md.update(dataBytes, 0, nread);
        };
        byte[] mdbytes = md.digest();
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < mdbytes.length; i++) {
            sb.append(Integer.toString((mdbytes[i] & 0xff) + 0x100, 16).substring(1));
        }
        System.out.println("Digest(in hex format):: " + sb.toString());
    }

Reference

http://download.oracle.com/javase/1.4.2/docs/api/java/security/MessageDigest.html

This Java MD5 encrypt example source code you can voluntariness use. If you have any comments please contact me.

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