Java Tutorial/Security/Mac

Generating a MAC from a text input using a random key.

import javax.crypto.Mac;
   import javax.crypto.spec.SecretKeySpec;
   import java.security.SecureRandom;
   import sun.misc.*;
   public class MainClass {
     public static void main (String[] args) throws Exception {
       SecureRandom random = new SecureRandom();
       byte[] keyBytes = new byte[20];
       random.nextBytes(keyBytes);
       SecretKeySpec key = new SecretKeySpec(keyBytes, "HMACSHA1");
       System.out.println("Key:"+new
                           BASE64Encoder().encode(key.getEncoded()));
       Mac mac = Mac.getInstance("HmacSHA1");
       mac.init(key);
       mac.update("test".getBytes("UTF8"));
       byte[] result = mac.doFinal();
       System.out.println("MAC: "+new BASE64Encoder().encode(result));
     }
   }

Generating a Message Authentication Code (MAC) Key

import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
public class Main {
  public static void main(String[] argv) throws Exception {
    KeyGenerator keyGen = KeyGenerator.getInstance("HmacMD5");
    SecretKey key = keyGen.generateKey();
    // Generate a key for the HMAC-SHA1 keyed-hashing algorithm
    keyGen = KeyGenerator.getInstance("HmacSHA1");
    key = keyGen.generateKey();
  }
}

Mac creation

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
public class MainClass {
  public static void main(String args[]) throws Exception {
    SecretKeySpec k = new SecretKeySpec("1234".getBytes(), "HMACSHA1");
    Mac m = Mac.getInstance("HmacMD5");
    m.init(k);
    m.update("test".getBytes("UTF8"));
    byte s[] = m.doFinal();
    for (int i = 0; i < s.length; i++) {
      System.out.print( Integer.toHexString((0x000000ff & s[i]) | 0xffffff00).substring(6));
    }
  }
}

Use MAC

import javax.crypto.KeyGenerator;
import javax.crypto.Mac;
import javax.crypto.SecretKey;
public class MainClass {
  public static void main(String[] args) throws Exception {
    String alg = "HmacMD5";
    Mac mac = Mac.getInstance(alg);
    KeyGenerator kg = KeyGenerator.getInstance(alg);
    SecretKey key = kg.generateKey();
    mac.init(key);
    mac.update("test".getBytes());
    byte[] b = mac.doFinal();
    System.out.println(new String(b));
  }
}