how can we encrypt and decrypt username and password

if (!IsPostBack)

{

base.Page_Load(sender, e);

FillAllRole();

if (Request.Cookies["UserName"] != null && Request.Cookies["Password"] != null)

{

txtUsername.Value = Request.Cookies["UserName"].Value;

txtPassword.Attributes.Add("value", Request.Cookies["Password"].Value);

chkRememberMe.Checked = true;

btnSubmit.Focus();

}

else

{

txtUsername.Value = String.Empty;

txtPassword.Text = String.Empty;

txtPassword.Attributes.Add("placeholder", "Password");

chkRememberMe.Checked = false;

txtUsername.Focus();

}

}

}

protected void BtnSubmit_ServerClick(object sender, EventArgs e)

{

try

{

btnSubmit.Disabled = true;

string userName = txtUsername.Value;

ViewState["userPassword"] = txtPassword.Text;

var objService = ServiceFactory.CreateSecurityService();

var validateUser = objService.IsValidUser(userName, ViewState["userPassword"].ToString(), String.Concat(ConfigurationManager.AppSettings["ADBaseDirectory"], ConfigurationManager.AppSettings["ADPath"]));

// var DefaultRole = objService.IsDefaultRoleMarked(userName);

if (validateUser.Item1 && validateUser.Item2 && validateUser.Item3 != Guid.Empty)

{

RememberMe(userName, ViewState["userPassword"].ToString());

//Response.Redirect("HomePage.aspx?LandingModuleID=" + CustomCryptoServiceProvider.Encrypt(validateUser.Item3.ToString()), false);

Response.Redirect(RedirectionFactory.GetPageName(validateUser.Item3), false);

}

else if (validateUser.Item1 && !validateUser.Item2)

{

foreach (var item in CustomAuthentication.GetUserRoleCollection())

ddlFirstTime.Items.Add(new ListItem(item.RoleName, (Convert.ToString(item.RoleID))));

txtUsername.Disabled = true;

txtPassword.Enabled = false;

lblFirstTime.Visible = true;

ddlFirstTime.Visible = true;

errorMsg.Visible = false;

imgbtnProceed.Visible = true;

btnSubmit.Visible = false;

lbRegister.Visible = false;

lblRememberMe.Visible = false;

chkRememberMe.Visible = false;

}

else if (!validateUser.Item1 && !validateUser.Item2)

{

errorMsg.Visible = true;

errorMsg.Text = Nihilent.PMOTracker.Common.Resource.ErrorMsgLogin;

btnSubmit.Disabled = false;

lblFirstTime.Visible = false;

ddlFirstTime.Visible = false;

imgbtnProceed.Visible = false;

}

}

catch (Exception ex)

{

btnSubmit.Disabled = false;

Elmah.ErrorSignal.FromCurrentContext().Raise(ex);

}

}

private void RememberMe(string userName, string userPassword)

{

if (chkRememberMe.Checked)

{

Response.Cookies["UserName"].Expires = DateTime.Now.AddDays(30);

Response.Cookies["Password"].Expires = DateTime.Now.AddDays(30);

}

else

{

Response.Cookies["UserName"].Expires = DateTime.Now.AddDays(-1);

Response.Cookies["Password"].Expires = DateTime.Now.AddDays(-1);

}

Response.Cookies["UserName"].Value = userName;

Response.Cookies["Password"].Value = userPassword;

}