Pass encrypted querystring between php and asp.net (c#)

I need to pass a single variable in a querystring from one application (in PHP) to another (in ASP.NET). It's a one way transfer...That is I need to encrypt it in PHP and decrypt it in ASP.NET (c#).

I'm barely a newbie on PHP and I'd like not to have to do more than add a tag to the page that needs to do the passing.

The data will be anywhere from 5 - 15 character开发者_C百科s..only letters and numbers.

Thanks!

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How about something like this?

<?
$query_string = base64_encode($_SERVER["QUERY_STRING"]);

header("location: http://www.domain.com/page.aspx?query_string=$query_string");

//rest of php code...
?>

Then in page.aspx you decode that query string