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);

        }

    }

}