/**
 * Company Name : 中贸促信息技术有限责任公司
 * Project Name:project
 * File Name:PasswordHash.java
 * Package Name:org.ccpit.base.utils
 * Date:2015年10月23日下午2:10:48
 * Copyright (c) 2015, dingwei@ccpit.org All Rights Reserved.
 *
 */

package org.ccpit.base.utils;

import java.math.BigInteger;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.spec.InvalidKeySpecException;

import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;

/**
 * ClassName:PasswordHash <br/>
 * Function: TODO ADD FUNCTION. <br/>
 * Reason: TODO ADD REASON. <br/>
 * Date: 2015年10月23日 下午2:10:48 <br/>
 * 
 * @author dingwei
 * @version
 * @since JDK 1.6
 * @see
 */
public class PasswordHash {

	public static final String PBKDF2_ALGORITHM = "PBKDF2WithHmacSHA1";

	// The following constants may be changed without breaking existing hashes.
	public static final int SALT_BYTE_SIZE = 24;
	public static final int HASH_BYTE_SIZE = 24;
	public static final int PBKDF2_ITERATIONS = 1000;

	public static final int ITERATION_INDEX = 0;
	public static final int SALT_INDEX = 1;
	public static final int PBKDF2_INDEX = 2;

	/**
	 * Returns a salted PBKDF2 hash of the password.
	 *
	 * @param password
	 *            the password to hash
	 * @return a salted PBKDF2 hash of the password
	 */
	public static String createHash(String password) throws NoSuchAlgorithmException, InvalidKeySpecException {
		return createHash(password.toCharArray());
	}

	/**
	 * Returns a salted PBKDF2 hash of the password.
	 *
	 * @param password
	 *            the password to hash
	 * @return a salted PBKDF2 hash of the password
	 */
	public static String createHash(char[] password) throws NoSuchAlgorithmException, InvalidKeySpecException {
		// Generate a random salt
		SecureRandom random = new SecureRandom();
		byte[] salt = new byte[SALT_BYTE_SIZE];
		random.nextBytes(salt);

		// Hash the password
		byte[] hash = pbkdf2(password, salt, PBKDF2_ITERATIONS, HASH_BYTE_SIZE);
		// format iterations:salt:hash
		return PBKDF2_ITERATIONS + ":" + toHex(salt) + ":" + toHex(hash);
	}

	/**
	 * Validates a password using a hash.
	 *
	 * @param password
	 *            the password to check
	 * @param correctHash
	 *            the hash of the valid password
	 * @return true if the password is correct, false if not
	 */
	public static boolean validatePassword(String password, String correctHash)
			throws NoSuchAlgorithmException, InvalidKeySpecException {
		return validatePassword(password.toCharArray(), correctHash);
	}

	/**
	 * Validates a password using a hash.
	 *
	 * @param password
	 *            the password to check
	 * @param correctHash
	 *            the hash of the valid password
	 * @return true if the password is correct, false if not
	 */
	public static boolean validatePassword(char[] password, String correctHash)
			throws NoSuchAlgorithmException, InvalidKeySpecException {
		// Decode the hash into its parameters
		String[] params = correctHash.split(":");
        if (params.length <= 1) {
            return false;
        }
        int iterations = Integer.parseInt(params[ITERATION_INDEX]);
		byte[] salt = fromHex(params[SALT_INDEX]);
		byte[] hash = fromHex(params[PBKDF2_INDEX]);
		// Compute the hash of the provided password, using the same salt,
		// iteration count, and hash length
		byte[] testHash = pbkdf2(password, salt, iterations, hash.length);
		// Compare the hashes in constant time. The password is correct if
		// both hashes match.
		return slowEquals(hash, testHash);
	}

	/**
	 * Compares two byte arrays in length-constant time. This comparison method
	 * is used so that password hashes cannot be extracted from an on-line
	 * system using a timing attack and then attacked off-line.
	 * 
	 * @param a
	 *            the first byte array
	 * @param b
	 *            the second byte array
	 * @return true if both byte arrays are the same, false if not
	 */
	private static boolean slowEquals(byte[] a, byte[] b) {
		int diff = a.length ^ b.length;
		for (int i = 0; i < a.length && i < b.length; i++)
			diff |= a[i] ^ b[i];
		return diff == 0;
	}

	/**
	 * Computes the PBKDF2 hash of a password.
	 *
	 * @param password
	 *            the password to hash.
	 * @param salt
	 *            the salt
	 * @param iterations
	 *            the iteration count (slowness factor)
	 * @param bytes
	 *            the length of the hash to compute in bytes
	 * @return the PBDKF2 hash of the password
	 */
	private static byte[] pbkdf2(char[] password, byte[] salt, int iterations,
			int bytes) throws NoSuchAlgorithmException, InvalidKeySpecException {
		PBEKeySpec spec = new PBEKeySpec(password, salt, iterations, bytes * 8);
		SecretKeyFactory skf = SecretKeyFactory.getInstance(PBKDF2_ALGORITHM);
		return skf.generateSecret(spec).getEncoded();
	}

	/**
	 * Converts a string of hexadecimal characters into a byte array.
	 *
	 * @param hex
	 *            the hex string
	 * @return the hex string decoded into a byte array
	 */
	private static byte[] fromHex(String hex) {
		byte[] binary = new byte[hex.length() / 2];
		for (int i = 0; i < binary.length; i++) {
			binary[i] = (byte) Integer.parseInt(
					hex.substring(2 * i, 2 * i + 2), 16);
		}
		return binary;
	}

	/**
	 * Converts a byte array into a hexadecimal string.
	 *
	 * @param array
	 *            the byte array to convert
	 * @return a length*2 character string encoding the byte array
	 */
	private static String toHex(byte[] array) {
		BigInteger bi = new BigInteger(1, array);
		String hex = bi.toString(16);
		int paddingLength = (array.length * 2) - hex.length();
		if (paddingLength > 0)
			return String.format("%0" + paddingLength + "d", 0) + hex;
		else
			return hex;
	}

	/**
	 * Tests the basic functionality of the PasswordHash class
	 *
	 * @param args
	 *            ignored
	 */
	public static void main(String[] args) {
		try {
			// Print out 10 hashes
			for (int i = 0; i < 10; i++)
				System.out.println(PasswordHash.createHash("p\r\nassw0Rd!"));

			// Test password validation
			boolean failure = false;
			System.out.println("Running tests...");
			for (int i = 0; i < 100; i++) {
				String password = "" + i;
				String hash = createHash(password);
				String secondHash = createHash(password);
				if (hash.equals(secondHash)) {
					System.out.println("FAILURE: TWO HASHES ARE EQUAL!");
					failure = true;
				}
				String wrongPassword = "" + (i + 1);
				if (validatePassword(wrongPassword, hash)) {
					System.out.println("FAILURE: WRONG PASSWORD ACCEPTED!");
					failure = true;
				}
				if (!validatePassword(password, hash)) {
					System.out.println("FAILURE: GOOD PASSWORD NOT ACCEPTED!");
					failure = true;
				}
			}
			if (failure)
				System.out.println("TESTS FAILED!");
			else
				System.out.println("TESTS PASSED!");
		} catch (Exception ex) {
			System.out.println("ERROR: " + ex);
		}
	}
}
