Android Open Source - APO-Theta-Upsilon-App Dynamic Hmac

• Back to App/event  ↑

From Project

Back to project page APO-Theta-Upsilon-App.

License

The source code is released under:

GNU Lesser General Public License

Java Source Code

/*
 * Copyright 2011 Devin Schwab, Umang Banugaria
 */*from w w  w .  jav a2  s  .c o  m*/
 * This file is part of the APO Theta Upsilon App for Case Western Reserve University's Alpha Phi Omega Theta Upsilon Chapter.
 *
 * The APO Theta Upsilon program is free software: you can redistribute it and/or modify
 * it under the terms of the Lesser GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * Lesser GNU General Public License for more details.
 *
 * You should have received a copy of the Lesser GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package edu.cwru.apo;

import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

public class DynamicHmac extends Hmac {
  
  private int counter = 0;
  private int increment = 0;
  
  public DynamicHmac()
  {
    SecureRandom random = new SecureRandom();
    secretKey = new byte[defaultKeyLength];
    random.nextBytes(secretKey);
  }
  
  public DynamicHmac(Hex secretKey, int counter, int increment)
  {
    this.secretKey = secretKey.toBytes();
    this.counter = counter;
    this.increment = increment;
  }
  
  public DynamicHmac(String mode, int keyLength)
  {
    SecureRandom random = new SecureRandom();
    secretKey = new byte[keyLength];
    random.nextBytes(secretKey);
    this.mode = mode;
  }
  
  public int getCounter()
  {
    return counter;
  }
  
  public int getIncrement()
  {
    return increment;
  }
  
  public void setCounter(int count)
  {
    counter = count;
  }
  
  public void setIncrement(int inc)
  {
    increment = inc;
  }
  
  public Hex generate(String data) throws InvalidKeyException,NoSuchAlgorithmException
  {
    if(secretKey == null)
      return null;
    SecretKeySpec sk = new SecretKeySpec(HOTP(), mode);
    Mac mac;
    mac = Mac.getInstance(mode);
      mac.init(sk);
      return new Hex(mac.doFinal(data.getBytes()));
  }
  
  private byte[] HOTP()
  {
    
    try {
      counter += increment;            //increments the counter to the next value
      if(secretKey == null)
        return null;
      SecretKeySpec sk = new SecretKeySpec(secretKey, mode);
      Mac mac;
      mac = Mac.getInstance(mode);
        mac.init(sk);
        
        //byte[] hmac_result =  mac.doFinal(intToBytes(counter));
        byte[] hmac_result =  mac.doFinal((""+counter).getBytes());

        // make sure the index will be inbounds
        if(hmac_result.length < 19)
          return null;
        
        // get the last 4 bits of the 19th byte of the hmac_result
        // this acts as an offset
        int offset = (int)(hmac_result[19] & 0xf); 
        
        // get the binary code
        int bin_code = (int)((hmac_result[offset] & 0x7f) << 24
                    | (hmac_result[offset+1] & 0xff) << 16
                    | (hmac_result[offset+2] & 0xff) << 8
                    | (hmac_result[offset+3] & 0xff));
        String secret = new Hex(secretKey).toString();
        return (""+bin_code).getBytes();
    } catch (InvalidKeyException e) {
      // TODO Auto-generated catch block
      counter -= increment;        //incase something goes wrong, counter will be returned to previous state
      e.printStackTrace();
    } catch (NoSuchAlgorithmException e) {
      // TODO Auto-generated catch block
      counter -= increment;        //incase something goes wrong, counter will be returned to previous state
      e.printStackTrace();
    }
    return null;
  }
  
  private byte[] intToBytes(int input)
  {
          return new byte[] {
                  (byte)(input >>> 24),
                  (byte)(input >>> 16),
                  (byte)(input >>> 8),
                  (byte)input};
  }

}

Java Source Code List

• Back to App/event  ↑