/// <summary>
    /// Hash a password using the OpenBSD bcrypt scheme.
    /// </summary>
    /// <param name="password">The password to hash.</param>
    /// <param name="salt">The salt to hash with (perhaps generated
    /// using <c>BCrypt.GenerateSalt</c>).</param>
    /// <returns>The hashed password.</returns>
    public static string HashPassword(string password, string salt)
    {
        if (password == null)
        {
            throw new ArgumentNullException("password");
        }
        if (salt == null)
        {
            throw new ArgumentNullException("salt");
        }

        char minor = (char)0;

        if (salt[0] != '$' || salt[1] != '2')
        {
            throw new ArgumentException("Invalid salt version");
        }

        int offset;

        if (salt[1] != '$')
        {
            minor = salt[2];
            if (minor != 'a' || salt[3] != '$')
            {
                throw new ArgumentException("Invalid salt revision");
            }
            offset = 4;
        }
        else
        {
            offset = 3;
        }

        // Extract number of rounds
        if (salt[offset + 2] > '$')
        {
            throw new ArgumentException("Missing salt rounds");
        }

        int rounds = Int32.Parse(salt.Substring(offset, 2), NumberFormatInfo.InvariantInfo);

        byte[] passwordBytes = Encoding.UTF8.GetBytes(password + (minor >= 'a' ? "\0" : String.Empty));
        byte[] saltBytes     = DecodeBase64(salt.Substring(offset + 3, 22),
                                            BCRYPT_SALT_LEN);

        BCryptAlgorithm bcrypt = new BCryptAlgorithm();

        byte[] hashed = bcrypt.CryptRaw(passwordBytes, saltBytes, rounds);

        StringBuilder rs = new StringBuilder();

        rs.Append("$2");
        if (minor >= 'a')
        {
            rs.Append(minor);
        }
        rs.Append('$');
        if (rounds < 10)
        {
            rs.Append('0');
        }
        rs.Append(rounds);
        rs.Append('$');
        rs.Append(EncodeBase64(saltBytes, saltBytes.Length));
        rs.Append(EncodeBase64(hashed,
                               (bf_crypt_ciphertext.Length * 4) - 1));

        return(rs.ToString());
    }