TwoFactorCodeChecker.java

/*******************************************************************************
 * Copyright (c) 2013, 2014 Lectorius, Inc.
 * Authors:
 * Vijay Pandurangan (vijayp@mitro.co)
 * Evan Jones (ej@mitro.co)
 * Adam Hilss (ahilss@mitro.co)
 *
 *
 *     This program is free software: you can redistribute it and/or modify
 *     it under the terms of the 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
 *     GNU General Public License for more details.
 *
 *     You should have received a copy of the GNU General Public License
 *     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *     
 *     You can contact the authors at inbound@mitro.co.
 *******************************************************************************/
package co.mitro.twofactor;

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

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

import org.apache.commons.codec.binary.Base32;

public class TwoFactorCodeChecker {
  private static final int WINDOW_SIZE = 5;

  public static boolean checkCode(String secret, long code, long timeMsec) {
    Base32 codec = new Base32();
    byte[] decodedKey = codec.decode(secret);
    long t = (timeMsec / 1000L) / 30L;
    for (int i = -WINDOW_SIZE; i <= WINDOW_SIZE; ++i) {
      long hash;
      try {
        hash = computeHash(decodedKey, t + i);
      } catch (Exception e) {
        e.printStackTrace();
        throw new RuntimeException(e.getMessage());
      }
      if (hash == code) {
        return true;
      }
    }
    return false;
  }

  public static int computeHash(byte[] key, long t)
      throws NoSuchAlgorithmException, InvalidKeyException {
    byte[] data = new byte[8];
    long value = t;
    for (int i = 8; i-- > 0; value >>>= 8) {
      data[i] = (byte) value;
    }
    SecretKeySpec signKey = new SecretKeySpec(key, "HmacSHA1");
    Mac mac = Mac.getInstance("HmacSHA1");
    mac.init(signKey);
    byte[] hash = mac.doFinal(data);
    int offset = hash[20 - 1] & 0xF;
    long truncatedHash = 0;
    for (int i = 0; i < 4; ++i) {
      truncatedHash <<= 8;
      truncatedHash |= (hash[offset + i] & 0xFF);
    }
    truncatedHash &= 0x7FFFFFFF;
    truncatedHash %= 1000000;
    return (int) truncatedHash;
  }
}