nip.php

<?php
function digitosAleatorios($longitud = 4)
{
	$caracteres = '0123456789';
	$cadenaAleatoria = '';
		for ($i = 0; $i < $longitud; $i++) {
			$cadenaAleatoria .= $caracteres[rand(0, strlen($caracteres) - 1)];
		}
	return $cadenaAleatoria;
}