C# implementation of WordPress PHPass

    public class phpBBCryptoServiceProvider
    {
        /// <summary>
        /// The encryption string base.
        /// </summary>
        private string itoa64 = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

        /// <summary>
        /// Compares the password string given with the hash retrieved from your database.
        /// </summary>
        /// <param name="password">Plaintext password.</param>
        /// <param name="hash">Hash from a SQL database</param>
        /// <returns>True if the password is correct, False otherwise.</returns>
        public bool phpbbCheckHash(string password, string hash)
        {
            if (hash.Length == 34) return (hashCryptPrivate(ASCIIEncoding.ASCII.GetBytes(password), hash, itoa64) == hash);
            return false;
        }

        /// <summary>
        /// This function will return the resulting hash from the password string you specify.
        /// </summary>
        /// <param name="password">String to hash.</param>
        /// <returns>Encrypted hash.</returns>
        /// <remarks>
        /// Although this will return the md5 for an older password, I have not added
        /// support for older passwords, so they will not work with this class unless
        /// I or someone else updates it.
        /// </remarks>
        public string phpbb_hash(string password)
        {
            // Generate a random string from a random number with the length of 6.
            // You could use a static string instead, doesn't matter. E.g.
            // byte[] random = ASCIIEncoding.ASCII.GetBytes("abc123");
            byte[] random = ASCIIEncoding.ASCII.GetBytes(new Random().Next(100000, 999999).ToString());

            string hash = hashCryptPrivate(ASCIIEncoding.ASCII.GetBytes(password), hashGensaltPrivate(random, itoa64), itoa64);

            if (hash.Length == 34) return hash;

            return sMD5(password);
        }

        /// <summary>
        /// The workhorse that encrypts your hash.
        /// </summary>
        /// <param name="password">String to be encrypted. Use: ASCIIEncoding.ASCII.GetBytes();</param>
        /// <param name="genSalt">Generated salt.</param>
        /// <param name="itoa64">The itoa64 string.</param>
        /// <returns>The encrypted hash ready to be compared.</returns>
        /// <remarks>
        /// password:  Saves conversion inside the function, lazy coding really.
        /// genSalt:   Returns from hashGensaltPrivate(random, itoa64);
        /// return:    Compare with phpbbCheckHash(password, hash)
        /// </remarks>
        private string hashCryptPrivate(byte[] password, string genSalt, string itoa64)
        {
            string output = "*";
            MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
            //if (!genSalt.StartsWith("$H$")) return output;
            if (!genSalt.StartsWith("$P$")) return output;
            //   $count_log2 = strpos($itoa64, $setting[3]);
            int count_log2 = itoa64.IndexOf(genSalt[3]);
            if (count_log2 < 7 || count_log2 > 30) return output;

            int count = 1 << count_log2;
            byte[] salt = ASCIIEncoding.ASCII.GetBytes(genSalt.Substring(4, 8));

            if (salt.Length != 8) return output;

            byte[] hash = md5.ComputeHash(Combine(salt, password));

            do
            {
                hash = md5.ComputeHash(Combine(hash, password));
            } while (count-- > 1);

            output = genSalt.Substring(0, 12);
            output += hashEncode64(hash, 16, itoa64);

            return output;
        }

        /// <summary>
        /// Private function to concat byte arrays.
        /// </summary>
        /// <param name="b1">Source array.</param>
        /// <param name="b2">Array to add to the source array.</param>
        /// <returns>Combined byte array.</returns>
        private byte[] Combine(byte[] b1, byte[] b2)
        {
            byte[] retVal = new byte[b1.Length + b2.Length];
            Array.Copy(b1, 0, retVal, 0, b1.Length);
            Array.Copy(b2, 0, retVal, b1.Length, b2.Length);
            return retVal;
        }

        /// <summary>
        /// Encode the hash.
        /// </summary>
        /// <param name="input">The hash to encode.</param>
        /// <param name="count">[This parameter needs documentation].</param>
        /// <param name="itoa64">The itoa64 string.</param>
        /// <returns>Encoded hash.</returns>
        private string hashEncode64(byte[] input, int count, string itoa64)
        {
            string output = "";
            int i = 0; int value = 0;

            do
            {
                value = input[i++];
                output += itoa64[value & 0x3f];

                if (i < count) value |= input[i] << 8;
                output += itoa64[(value >> 6) & 0x3f];
                if (i++ >= count)
                    break;

                if (i < count) value |= input[i] << 16;
                output += itoa64[(value >> 12) & 0x3f];
                if (i++ >= count)
                    break;

                output += itoa64[(value >> 18) & 0x3f];

            } while (i < count);

            return output;
        }

        /// <summary>
        /// Generate salt for hash generation.
        /// </summary>
        /// <param name="input">Any random information.</param>
        /// <param name="itoa64">The itoa64 string.</param>
        /// <returns>Generated salt string</returns>
        private string hashGensaltPrivate(byte[] input, string itoa64)
        {
            //int iteration_count_log2 = 6;
            int iteration_count_log2 = 8;

            //string output = "$H$";
            string output = "$P$";
            output += itoa64[Math.Min(iteration_count_log2 + 5, 30)];
            output += hashEncode64(input, 6, itoa64);

            return output;
        }

        /// <summary>
        /// Returns a hexadecimal string representation for the encrypted MD5 parameter.
        /// </summary>
        /// <param name="password">String to be encrypted.</param>
        /// <returns>String</returns>
        private string sMD5(string password) { return sMD5(password, false); }

        /// <summary>
        /// Returns a hexadecimal string representation for the encrypted MD5 parameter.
        /// </summary>
        /// <param name="password">String to be encrypted.</param>
        /// <param name="raw">Whether or not to produce a raw string.</param>
        /// <returns>String</returns>
        private string sMD5(string password, bool raw)
        {
            MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
            if (raw) return Encoding.ASCII.GetString(md5.ComputeHash(Encoding.ASCII.GetBytes(password)));
            else return BitConverter.ToString(md5.ComputeHash(Encoding.ASCII.GetBytes(password))).Replace("-", "");
        }
    }