How to use same randomly generated value in header.php and footer.php in wordpress

I want to use same randomly generated value in header.php and footer.php in wordpress. i have try this function to randomly generated value:

function randValue() {
$randCheaters = substr(md5(microtime()),rand(0,26),5);
return $randCheaters;
}

In header.php i use some thing like this

<header id="<? echo randValue(); ?>">

and in footer.php i have used this

<footer id="<? echo randValue(); ?>">

The problem is it generate different value in footer and header, how can i get the same value in both place.