Java md5 example with MessageDigest

You can use BigInteger to do the byte array conversion....

    static String getMd5Digest(String input)
        {
            try
            {
                MessageDigest md = MessageDigest.getInstance("MD5");
                byte[] messageDigest = md.digest(input.getBytes());
                BigInteger number = new BigInteger(1,messageDigest);
                return number.toString(16);
            }
            catch(NoSuchAlgorithmException e)
            {
                throw new RuntimeException(e);
            }
        }

public String getMD5Hash(String value)
throws NoSuchAlgorithmException, UnsupportedEncodingException {

final StringBuilder sbMd5Hash = new StringBuilder();
final MessageDigest m = MessageDigest.getInstance("MD5");
m.update(value.getBytes("UTF-8"));

final byte data[] = m.digest();

for (byte element : data) {
sbMd5Hash.append(Character.forDigit((element >> 4) & 0xf, 16));
sbMd5Hash.append(Character.forDigit(element & 0xf, 16));
}

return sbMd5Hash.toString();
}

BigInteger is not correct for example "Cash"
with BigInteger = 69b30db06d047a398f9eb0940d3279c
Right is = 069b30db06d047a398f9eb0940d3279c

import java.security.*;
import java.io.*;
import java.math.BigInteger;

public class Checksum {

    //
    // returns 0 error
    //         1 ok (create)
    //         1 same (check)
    //         2 different (check)
    //
    public static void main(String args[]) {
        if (args.length == 2) {
            if (args[0].equalsIgnoreCase("create")) {
                System.exit(new Checksum().create(args[1]));
            } else if (args[0].equalsIgnoreCase("check")) {
                System.exit(new Checksum().check(args[1]));
            }
        } else {
            System.out.println("Usage : java Checksum create [filename]n" +
                    "        java Checksum check  [filename]");
        }
    }

    public int create(String filename) {
        try {
            int sum;
            String salida = new String();
            byte[] chk = createChecksum(filename);
            File f = new File(filename + ".chk");
            OutputStream os = new FileOutputStream(f);
            //muestra la cadena MD5 y es la misma quela del program MD5Check.exe
            BigInteger bigInt = new BigInteger(1, chk);
            String output = bigInt.toString(16).toUpperCase();;
            if (output.length() < 32){
				System.out.println("Menor de 32");
                sum = 32 - output.length();
                for ( int i = 1 ; i == sum;i++){
                    salida=salida.concat("0");
                }
                salida = salida.concat(output);
            }
            System.out.println("MD5: " + output+" = "+ salida);
            os.write(chk);
            os.close();
            return 1;
        } catch (Exception e) {
            e.printStackTrace();
            return 0;
        }
    }

    public int check(String filename) {
        int rc = 0;
        try {
            byte[] chk1 = createChecksum(filename);
            byte[] chk2 = new byte[chk1.length];
            File f = new File(filename + ".chk");
            InputStream is = new FileInputStream(f);

            is.read(chk2);
            //muestra la cadena MD5 y es la misma quela del program MD5Check.exe
            BigInteger bigInt1 = new BigInteger(1, chk1);
            String output1 = bigInt1.toString(16).toUpperCase();;
            System.out.println("MD5: " + filename + "     " + output1);
            BigInteger bigInt2 = new BigInteger(1, chk2);
            String output2 = bigInt2.toString(16).toUpperCase();;
            System.out.println("MD5: " + filename + ".chk " + output2);
            //fin muestra
            //if (new String(chk2).equals(new String(chk1))) {
            if (output2.equals(output1)) {
                System.out.println("Same!");
                rc = 1;
            } else {
                System.out.println("Different!");
                rc = 2;
            }
            is.close();
            return rc;
        } catch (Exception e) {
            e.printStackTrace();
            return rc;
        }
    }

    public byte[] createChecksum(String filename) throws Exception {
        InputStream fis = new FileInputStream(filename);

        byte[] buffer = new byte[1024];
        MessageDigest complete = MessageDigest.getInstance("MD5");
        int numRead;
        do {
            numRead = fis.read(buffer);
            if (numRead > 0) {
                complete.update(buffer, 0, numRead);
            }
        } while (numRead != -1);
        fis.close();
        return complete.digest();
    }
}

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class Md5Digester {
private static final char[] DIGITS = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };

private static MessageDigest md5;

static {
try {
md5 = MessageDigest.getInstance("MD5");
}
catch (NoSuchAlgorithmException e) {
throw new RuntimeException("Could not create an instance of MD5 MessageDigest");
}
}

public Md5Digester() {
}

public static byte[] digest(File file) throws IOException {
md5.reset();
return md5.digest(getBytesFromFile(file));
}

public static byte[] digest(String string) {
return md5.digest(string.getBytes());
}

public static String encodeHex(byte[] data) {
int l = data.length;
char[] out = new char[l << 1];
// two characters form the hex value.
for (int i = 0, j = 0; i < l; i++) {
out[j++] = DIGITS[(0xF0 & data) >>> 4];
out[j++] = DIGITS[0x0F & data[i]];
}
return new String(out);
}

private static byte[] getBytesFromFile(File file) throws IOException {
if (file == null) {
throw new IllegalArgumentException("Argument: file cannot be NULL");
}
if (!file.exists() && !file.isFile()) {
throw new IllegalArgumentException("Arument: file must be a file (not directory etc) and must exist");
}

InputStream is = new FileInputStream(file);

long length = file.length();
byte[] bytes = new byte[(int) length];

int offset = 0;
int numRead = 0;
while (offset < bytes.length && (numRead = is.read(bytes, offset, bytes.length - offset)) >= 0) {
offset += numRead;
}

if (offset < bytes.length) {
throw new IOException("Could not completely read file " + file.getName());
}

is.close();
return bytes;
}

}

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class Md5Digester {
private static final char[] DIGITS = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };

private static MessageDigest md5;

static {
try {
md5 = MessageDigest.getInstance("MD5");
}
catch (NoSuchAlgorithmException e) {
throw new RuntimeException("Could not create an instance of MD5 MessageDigest");
}
}

public Md5Digester() {
}

public static byte[] digest(File file) throws IOException {
md5.reset();
return md5.digest(getBytesFromFile(file));
}

public static byte[] digest(String string) {
return md5.digest(string.getBytes());
}

public static String encodeHex(byte[] data) {
int l = data.length;
char[] out = new char[l << 1];
// two characters form the hex value.
for (int i = 0, j = 0; i < l; i++) {
out[j++] = DIGITS[(0xF0 & data) >>> 4];
out[j++] = DIGITS[0x0F & data[i]];
}
return new String(out);
}

private static byte[] getBytesFromFile(File file) throws IOException {
if (file == null) {
throw new IllegalArgumentException("Argument: file cannot be NULL");
}
if (!file.exists() && !file.isFile()) {
throw new IllegalArgumentException("Arument: file must be a file (not directory etc) and must exist");
}

InputStream is = new FileInputStream(file);

long length = file.length();
byte[] bytes = new byte[(int) length];

int offset = 0;
int numRead = 0;
while (offset < bytes.length && (numRead = is.read(bytes, offset, bytes.length - offset)) >= 0) {
offset += numRead;
}

if (offset < bytes.length) {
throw new IOException("Could not completely read file " + file.getName());
}

is.close();
return bytes;
}

}

This is a quick tip for implementing md5 encryption in java. We use the MessageDigest class in the java.security package and some string manipulation to turn the plain text into a byte array. The digest is then updated from the bytes from the byte array and a hash computation is conducted upon them. To quote from the Sun java api docs, The MessageDigest class provides applications the functionality of a message digest algorithm, such as MD5 or SHA. Message digests are secure one-way hash functions that take arbitrary-sized data and output a fixed-length hash value.

Anyway the md5 example code below takes a session id (this is just a string which I wanted to encrypt - It could just as easily be a document, say a lump of xml or any old bit of text). This session id is pulled into the bytes array, defaultBytes and then the MessageDigest is instantiated as an instance of an md5 encryption.

Java developers who have come over from PERL or PHP often get frustrated with such a longwinded means of running what could simply be a single line of code, however the snippet below could be wrapped into an md5sum class which conducts the encryption and simply returns a string of cipher text.

include java.security.*;

... etc

sessionid="12345";
        
byte[] defaultBytes = sessionid.getBytes();
try{
	MessageDigest algorithm = MessageDigest.getInstance("MD5");
	algorithm.reset();
	algorithm.update(defaultBytes);
	byte messageDigest[] = algorithm.digest();
            
	StringBuffer hexString = new StringBuffer();
	for (int i=0;i<messageDigest.length;i++) {
		hexString.append(Integer.toHexString(0xFF & messageDigest[i]));
	}
	String foo = messageDigest.toString();
	System.out.println("sessionid "+sessionid+" md5 version is "+hexString.toString());
	sessionid=hexString+"";
}catch(NoSuchAlgorithmException nsae){
            
}

Remember to import the java.security package. The original plain text and cipher text strings are echod to the java console just to demonstrate what has happened.


Hope that's useful,

christo

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