private bool UserExists(string Username, string Password)
    {
        using (var con = new MySqlConnection(_connectionString))
        {
            con.Open();
            MySqlCommand cmd = con.CreateCommand();
            cmd.CommandType = CommandType.Text;
            cmd.CommandText =
                @"SELECT *
                    FROM user
                   WHERE username= @username
                   AND password= @password";
            cmd.Parameters.AddWithValue("@username", bxUserName.Text);
            cmd.Parameters.AddWithValue("@password", bxPassword.Text = GenerateSHA256Hash(bxPassword.Text, salt));
            cmd.ExecuteNonQuery();
            DataTable dt = new DataTable();
            MySqlDataAdapter da = new MySqlDataAdapter(cmd);
            da.Fill(dt);
            using (var reader = cmd.ExecuteReader())
            {
                return (reader.Read());
            }
        }
    }

private void updatePassword()
    {

        String salt = CreateSalt(10);
        String hashedpassword = GenerateSHA256Hash(txtPassword.Text, salt);

        using (var con = new MySqlConnection(_connectionString))
        {
            con.Open();
            MySqlCommand cmd = con.CreateCommand();
            cmd.CommandType = CommandType.Text;
            cmd.CommandText =
                @"UPDATE user
                    SET password=@password, salt=@salt WHERE username= @username";
            cmd.Parameters.AddWithValue("@password", txtPassword.Text = GenerateSHA256Hash(txtPassword.Text, salt));
            cmd.Parameters.AddWithValue("@salt", txtPassword.Text = salt);
            cmd.Parameters.AddWithValue("@username", txtUserName.Text);
            cmd.ExecuteNonQuery();
            lblEditPW.Show();
        }
    }

    public String GenerateSHA256Hash(String input, String salt)
    {
        byte[] bytes = System.Text.Encoding.UTF8.GetBytes(input + salt);
        System.Security.Cryptography.SHA256Managed sha256hashstring =
             new System.Security.Cryptography.SHA256Managed();
        byte[] hash = sha256hashstring.ComputeHash(bytes);
        var sb = new StringBuilder();
        foreach (byte b in hash) sb.AppendFormat("{0:x2}", b);
        return sb.ToString();
    }


    public String CreateSalt(int size)
    {
        RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
        byte[] buffer = new byte[8];
        rng.GetBytes(buffer);
        string salt = BitConverter.ToString(buffer);
        return Convert.ToBase64String(buffer);
    }