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// Copyright (c) 2003-present, Jodd Team (http://jodd.org)
// 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
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// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.

package jodd.crypt;

import jodd.util.StringUtil;

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

public class PBKDF2Hash {

	private static final String PBKDF2_ALGORITHM = "PBKDF2WithHmacSHA512";

	private final int saltBytes;
	private final int hashBytes;
	private final int pbkdf2Iterations;

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

	public PBKDF2Hash() {
		this(24, 24, 1000);
	}
	public PBKDF2Hash(final int saltBytes, final int hashBytes, final int iterations) {
		this.saltBytes = saltBytes;
		this.hashBytes = hashBytes;
		this.pbkdf2Iterations = iterations;
	}

	/**
	 * Returns a salted PBKDF2 hash of the password.
	 *
	 * @param password the password to hash
	 * @return a salted PBKDF2 hash of the password
	 */
	public String createHash(final String password) {
		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 String createHash(final char[] password) {

		// Generate a random salt
		SecureRandom random = new SecureRandom();
		byte[] salt = new byte[saltBytes];
		random.nextBytes(salt);

		// Hash the password
		byte[] hash = pbkdf2(password, salt, pbkdf2Iterations, hashBytes);

		// format iterations:salt:hash
		return pbkdf2Iterations + ":" + StringUtil.toHexString(salt) + ":" + StringUtil.toHexString(hash);
	}

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

	/**
	 * Validates a password using a hash.
	 *
	 * @param password the password to check
	 * @param goodHash the hash of the valid password
	 * @return true if the password is correct, false if not
	 */
	public boolean validatePassword(final char[] password, final String goodHash) {
		// Decode the hash into its parameters
		String[] params = goodHash.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(final byte[] a, final 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(final char[] password, final byte[] salt, final int iterations, final int bytes) {
		PBEKeySpec spec = new PBEKeySpec(password, salt, iterations, bytes * 8);
		try {
			SecretKeyFactory skf = SecretKeyFactory.getInstance(PBKDF2_ALGORITHM);
			return skf.generateSecret(spec).getEncoded();
		}
		catch (NoSuchAlgorithmException ignore) {
			return null;
		}
		catch (InvalidKeySpecException e) {
			throw new IllegalArgumentException(e);
		}
	}

	/**
	 * 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(final String hex) {
		final 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;
	}

}