/**
 * Copyright (C) 2016 Hurence (bailet.thomas@gmail.com)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *         http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.hurence.logisland.util.string;

/* 
 * Password Hashing With PBKDF2 (http://crackstation.net/hashing-security.htm).
 * Copyright (c) 2013, Taylor Hornby
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, 
 * this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation 
 * and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE 
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
 * POSSIBILITY OF SUCH DAMAGE.
 */

import java.security.SecureRandom;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.SecretKeyFactory;
import java.math.BigInteger;
import java.security.NoSuchAlgorithmException;
import java.security.spec.InvalidKeySpecException;

/*
 * PBKDF2 salted password hashing.
 * Author: havoc AT defuse.ca
 * www: http://crackstation.net/hashing-security.htm
 */
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 = 8;
    public static final int HASH_BYTE_SIZE = 16;
    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(":");
	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 (NoSuchAlgorithmException | InvalidKeySpecException ex) {
	    System.out.println("ERROR: " + ex);
	}
    }

}
