hash("hello") = 2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824
hash("hbllo") = 58756879c05c68dfac9866712fad6a93f8146f337a69afe7dd238f3364946366
hash("waltz") = c0e81794384491161f1777c232bc6bd9ec38f616560b120fda8e90f383853542

1. 用户创建自己的账号
2. 用户密码经过hash操作之后存储在数据库中。没有任何明文的密码存储在服务器的硬盘上。
3. 用户登陆的时候，将用户输入的密码进行hash操作后与数据库里保存的密码hash值进行对比。
4. 如果hash值完全一样，则认为用户输入的密码是正确的。否则就认为用户输入了无效的密码。
5. 每次用户尝试登陆的时候就重复步骤3和步骤4。

Dictionary Attack

Trying apple        : failed
Trying blueberry    : failed
Trying justinbeiber : failed
...
Trying letmein      : failed
Trying s3cr3t       : success!

Brute Force Attack

Trying aaaa : failed
Trying aaab : failed
Trying aaac : failed
...
Trying acdb : failed
Trying acdc : success!

c11083b4b0a7743af748c85d343dfee9fbb8b2576c05f3a7f0d632b0926aadfc
08eac03b80adc33dc7d8fbe44b7c7b05d3a2c511166bdb43fcb710b03ba919e7
e4ba5cbd251c98e6cd1c23f126a3b81d8d8328abc95387229850952b3ef9f904
5206b8b8a996cf5320cb12ca91c7b790fba9f030408efe83ebb83548dc3007bd

Searching for hash(apple) in users' hash list...     : Matches [alice3, 0bob0, charles8]
Searching for hash(blueberry) in users' hash list... : Matches [usr10101, timmy, john91]
Searching for hash(letmein) in users' hash list...   : Matches [wilson10, dragonslayerX, joe1984]
Searching for hash(s3cr3t) in users' hash list...    : Matches [bruce19, knuth1337, john87]
Searching for hash(z@29hjja) in users' hash list...  : No users used this password

hash("hello")                    = 2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824
hash("hello" + "QxLUF1bgIAdeQX") = 9e209040c863f84a31e719795b2577523954739fe5ed3b58a75cff2127075ed1
hash("hello" + "bv5PehSMfV11Cd") = d1d3ec2e6f20fd420d50e2642992841d8338a314b8ea157c9e18477aaef226ab
hash("hello" + "YYLmfY6IehjZMQ") = a49670c3c18b9e079b9cfaf51634f563dc8ae3070db2c4a8544305df1b60f007

md5(sha1(password))
md5(md5(salt) + md5(password))
sha1(sha1(password))
sha1(str_rot13(password + salt))
md5(sha1(md5(md5(password) + sha1(password)) + md5(password)))

1. 使用CSPRNG生成一个长的随机盐。
2. 将密码和盐拼接在一起，使用标准的加密hash函数比如SHA256进行hash
3. 将盐和hash记录在用户数据库中

1. 从数据库中取出用户的盐和hash
2. 将用户输入的密码和盐按相同方式拼接在一起，使用相同的hash函数进行hash
3. 比较计算出的hash跟存储的hash是否相同。如果相同则密码正确。反之则密码错误。

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;
}

MOV EAX, [A]
CMP [B], EAX
JZ equal
JMP done
equal:
AND [VALID], 1
done:
AND [VALID], 0

MOV EAX, [A]
XOR EAX, [B]
OR [DIFF], EAX 

<?php
/*
 * 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.
 */

// These constants may be changed without breaking existing hashes.
define("PBKDF2_HASH_ALGORITHM", "sha256");
define("PBKDF2_ITERATIONS", 1000);
define("PBKDF2_SALT_BYTE_SIZE", 24);
define("PBKDF2_HASH_BYTE_SIZE", 24);

define("HASH_SECTIONS", 4);
define("HASH_ALGORITHM_INDEX", 0);
define("HASH_ITERATION_INDEX", 1);
define("HASH_SALT_INDEX", 2);
define("HASH_PBKDF2_INDEX", 3);

function create_hash($password)
{
    // format: algorithm:iterations:salt:hash
    $salt = base64_encode(mcrypt_create_iv(PBKDF2_SALT_BYTE_SIZE, MCRYPT_DEV_URANDOM));
    return PBKDF2_HASH_ALGORITHM . ":" . PBKDF2_ITERATIONS . ":" .  $salt . ":" .
        base64_encode(pbkdf2(
            PBKDF2_HASH_ALGORITHM,
            $password,
            $salt,
            PBKDF2_ITERATIONS,
            PBKDF2_HASH_BYTE_SIZE,
            true
        ));
}

function validate_password($password, $correct_hash)
{
    $params = explode(":", $correct_hash);
    if(count($params) < HASH_SECTIONS)
       return false;
    $pbkdf2 = base64_decode($params[HASH_PBKDF2_INDEX]);
    return slow_equals(
        $pbkdf2,
        pbkdf2(
            $params[HASH_ALGORITHM_INDEX],
            $password,
            $params[HASH_SALT_INDEX],
            (int)$params[HASH_ITERATION_INDEX],
            strlen($pbkdf2),
            true
        )
    );
}

// Compares two strings $a and $b in length-constant time.
function slow_equals($a, $b)
{
    $diff = strlen($a) ^ strlen($b);
    for($i = 0; $i < strlen($a) && $i < strlen($b); $i++)
    {
        $diff |= ord($a[$i]) ^ ord($b[$i]);
    }
    return $diff === 0;
}

/*
 * PBKDF2 key derivation function as defined by RSA's PKCS #5: https://www.ietf.org/rfc/rfc2898.txt
 * $algorithm - The hash algorithm to use. Recommended: SHA256
 * $password - The password.
 * $salt - A salt that is unique to the password.
 * $count - Iteration count. Higher is better, but slower. Recommended: At least 1000.
 * $key_length - The length of the derived key in bytes.
 * $raw_output - If true, the key is returned in raw binary format. Hex encoded otherwise.
 * Returns: A $key_length-byte key derived from the password and salt.
 *
 * Test vectors can be found here: https://www.ietf.org/rfc/rfc6070.txt
 *
 * This implementation of PBKDF2 was originally created by https://defuse.ca
 * With improvements by http://www.variations-of-shadow.com
 */
function pbkdf2($algorithm, $password, $salt, $count, $key_length, $raw_output = false)
{
    $algorithm = strtolower($algorithm);
    if(!in_array($algorithm, hash_algos(), true))
        trigger_error('PBKDF2 ERROR: Invalid hash algorithm.', E_USER_ERROR);
    if($count <= 0 || $key_length <= 0)
        trigger_error('PBKDF2 ERROR: Invalid parameters.', E_USER_ERROR);

    if (function_exists("hash_pbkdf2")) {
        // The output length is in NIBBLES (4-bits) if $raw_output is false!
        if (!$raw_output) {
            $key_length = $key_length * 2;
        }
        return hash_pbkdf2($algorithm, $password, $salt, $count, $key_length, $raw_output);
    }

    $hash_length = strlen(hash($algorithm, "", true));
    $block_count = ceil($key_length / $hash_length);

    $output = "";
    for($i = 1; $i <= $block_count; $i++) {
        // $i encoded as 4 bytes, big endian.
        $last = $salt . pack("N", $i);
        // first iteration
        $last = $xorsum = hash_hmac($algorithm, $last, $password, true);
        // perform the other $count - 1 iterations
        for ($j = 1; $j < $count; $j++) {
            $xorsum ^= ($last = hash_hmac($algorithm, $last, $password, true));
        }
        $output .= $xorsum;
    }

    if($raw_output)
        return substr($output, 0, $key_length);
    else
        return bin2hex(substr($output, 0, $key_length));
}
?>

/* 
 * 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 = 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(":");
        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);
        }
    }

}

/* 
 * 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.
 */

using System;
using System.Text;
using System.Security.Cryptography;

namespace PasswordHash
{
    /// <summary>
    /// Salted password hashing with PBKDF2-SHA1.
    /// Author: havoc AT defuse.ca
    /// www: http://crackstation.net/hashing-security.htm
    /// Compatibility: .NET 3.0 and later.
    /// </summary>
    public class PasswordHash
    {
        // The following constants may be changed without breaking existing hashes.
        public const int SALT_BYTE_SIZE = 24;
        public const int HASH_BYTE_SIZE = 24;
        public const int PBKDF2_ITERATIONS = 1000;

        public const int ITERATION_INDEX = 0;
        public const int SALT_INDEX = 1;
        public const int PBKDF2_INDEX = 2;

        /// <summary>
        /// Creates a salted PBKDF2 hash of the password.
        /// </summary>
        /// <param name="password">The password to hash.</param>
        /// <returns>The hash of the password.</returns>
        public static string CreateHash(string password)
        {
            // Generate a random salt
            RNGCryptoServiceProvider csprng = new RNGCryptoServiceProvider();
            byte[] salt = new byte[SALT_BYTE_SIZE];
            csprng.GetBytes(salt);

            // Hash the password and encode the parameters
            byte[] hash = PBKDF2(password, salt, PBKDF2_ITERATIONS, HASH_BYTE_SIZE);
            return PBKDF2_ITERATIONS + ":" +
                Convert.ToBase64String(salt) + ":" +
                Convert.ToBase64String(hash);
        }

        /// <summary>
        /// Validates a password given a hash of the correct one.
        /// </summary>
        /// <param name="password">The password to check.</param>
        /// <param name="correctHash">A hash of the correct password.</param>
        /// <returns>True if the password is correct. False otherwise.</returns>
        public static bool ValidatePassword(string password, string correctHash)
        {
            // Extract the parameters from the hash
            char[] delimiter = { ':' };
            string[] split = correctHash.Split(delimiter);
            int iterations = Int32.Parse(split[ITERATION_INDEX]);
            byte[] salt = Convert.FromBase64String(split[SALT_INDEX]);
            byte[] hash = Convert.FromBase64String(split[PBKDF2_INDEX]);

            byte[] testHash = PBKDF2(password, salt, iterations, hash.Length);
            return SlowEquals(hash, testHash);
        }

        /// <summary>
        /// Compares two byte arrays in length-constant time. This comparison
        /// method is used so that password hashes cannot be extracted from
        /// on-line systems using a timing attack and then attacked off-line.
        /// </summary>
        /// <param name="a">The first byte array.</param>
        /// <param name="b">The second byte array.</param>
        /// <returns>True if both byte arrays are equal. False otherwise.</returns>
        private static bool SlowEquals(byte[] a, byte[] b)
        {
            uint diff = (uint)a.Length ^ (uint)b.Length;
            for (int i = 0; i < a.Length && i < b.Length; i++)
                diff |= (uint)(a[i] ^ b[i]);
            return diff == 0;
        }

        /// <summary>
        /// Computes the PBKDF2-SHA1 hash of a password.
        /// </summary>
        /// <param name="password">The password to hash.</param>
        /// <param name="salt">The salt.</param>
        /// <param name="iterations">The PBKDF2 iteration count.</param>
        /// <param name="outputBytes">The length of the hash to generate, in bytes.</param>
        /// <returns>A hash of the password.</returns>
        private static byte[] PBKDF2(string password, byte[] salt, int iterations, int outputBytes)
        {
            Rfc2898DeriveBytes pbkdf2 = new Rfc2898DeriveBytes(password, salt);
            pbkdf2.IterationCount = iterations;
            return pbkdf2.GetBytes(outputBytes);
        }
    }
}

# 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.

require 'securerandom'
require 'openssl'
require 'base64'

# Salted password hashing with PBKDF2-SHA1.
# Authors: @RedragonX (dicesoft.net), havoc AT defuse.ca 
# www: http://crackstation.net/hashing-security.htm
module PasswordHash

  # The following constants can be changed without breaking existing hashes.
  PBKDF2_ITERATIONS = 1000
  SALT_BYTE_SIZE = 24
  HASH_BYTE_SIZE = 24

  HASH_SECTIONS = 4
  SECTION_DELIMITER = ':'
  ITERATIONS_INDEX = 1
  SALT_INDEX = 2
  HASH_INDEX = 3

  # Returns a salted PBKDF2 hash of the password.
  def self.createHash( password )
    salt = SecureRandom.base64( SALT_BYTE_SIZE )
    pbkdf2 = OpenSSL::PKCS5::pbkdf2_hmac_sha1(
      password,
      salt,
      PBKDF2_ITERATIONS,
      HASH_BYTE_SIZE
    )
    return ["sha1", PBKDF2_ITERATIONS, salt, Base64.encode64( pbkdf2 )].join( SECTION_DELIMITER )
  end

  # Checks if a password is correct given a hash of the correct one.
  # correctHash must be a hash string generated with createHash.
  def self.validatePassword( password, correctHash )
    params = correctHash.split( SECTION_DELIMITER )
    return false if params.length != HASH_SECTIONS

    pbkdf2 = Base64.decode64( params[HASH_INDEX] )
    testHash = OpenSSL::PKCS5::pbkdf2_hmac_sha1(
      password,
      params[SALT_INDEX],
      params[ITERATIONS_INDEX].to_i,
      pbkdf2.length
    )

    return pbkdf2 == testHash
  end

  # Run tests to ensure the module is functioning properly.
  # Returns true if all tests succeed, false if not.
  def self.runSelfTests
    puts "Sample hashes:"
    3.times { puts createHash("password") }

    puts "\nRunning self tests..."
    @@allPass = true

    correctPassword = 'aaaaaaaaaa'
    wrongPassword = 'aaaaaaaaab'
    hash = createHash(correctPassword)

    assert( validatePassword( correctPassword, hash ) == true, "correct password" )
    assert( validatePassword( wrongPassword, hash ) == false, "wrong password" )

    h1 = hash.split( SECTION_DELIMITER )
    h2 = createHash( correctPassword ).split( SECTION_DELIMITER )
    assert( h1[HASH_INDEX] != h2[HASH_INDEX], "different hashes" )
    assert( h1[SALT_INDEX] != h2[SALT_INDEX], "different salt" )

    if @@allPass
      puts "*** ALL TESTS PASS ***"
    else
      puts "*** FAILURES ***"
    end

    return @@allPass
  end

  def self.assert( truth, msg )
    if truth
      puts "PASS [#{msg}]"
    else
      puts "FAIL [#{msg}]"
      @@allPass = false
    end
  end

end

PasswordHash.runSelfTests