Cookies Setting For Particular Page Only

As far as I can tell, and it makes sense, when I set cookies for a page, say like this:
HTML Code:
<script>
function setCookie(cookie_name,value){
var cookie_value=escape(value);
document.cookie=c_name + "=" + cookie_value;
}
</script>

It works just fine, but it only sets the cookies for that particular page. Unfortunately I need it to remember that for all pages. In essence, this code belongs to a sign in page, but I need it to remember the username and password on all pages. I would like to avoid sending variables from page to page containing usernames and passwords if it's at all possible.