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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
// 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.

package jodd.util;

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

public class PBKDF2Hash {

    public static final String PBKDF2_ALGORITHM = "PBKDF2WithHmacSHA1";

    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(int saltBytes, int hashBytes, 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(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(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 + ":" + toHex(salt) + ":" + toHex(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(String password, 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(char[] password, 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(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) {
        PBEKeySpec spec = new PBEKeySpec(password, salt, iterations, bytes * 8);
        SecretKeyFactory skf = null;
        try {
            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(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", Integer.valueOf(0)) + hex;
        }
        return hex;
    }

}