Prevent Copy from Textbox to another

create a website and add Default.aspx page and in it add two Textbox
now we want to prevent copy from Textbox1 to Textbox2

First thing use this Javascript code:

function noCopyMouse(e)
{
var isRight = (e.button) ? (e.button == 2) : (e.which == 3);
if(isRight)
{
alert('You are prompted to type this twice for a reason!');
return false;
} return true;
}
function noCopyKey(e)
{
var forbiddenKeys = new Array('c','x','v');
var keyCode = (e.keyCode) ? e.keyCode : e.which;
var isCtrl;
if(window.event)
isCtrl = e.ctrlKey
else
isCtrl = (window.Event) ? ((e.modifiers & Event.CTRL_MASK) == Event.CTRL_MASK) : false;
if(isCtrl)
{
for(i = 0; i < forbiddenKeys.length; i++)
{
if(forbiddenKeys[i] == String.fromCharCode(keyCode).toLowerCase())
{
alert('You are prompted to type this twice for a reason!');
return false;
}
}
}
return true;
}

and in Default.aspx.cs

protected void Page_Load(object sender, EventArgs e)
{
if(!IsPostBack)
{
Textbox1.Attributes.Add("onmousedown", "return noCopyMouse(event);") Textbox1.Attributes.Add("onkeydown", "return noCopyKey(event);")
}
}