<?php

class SignedParam {
    private static $key = null;

    private $param;
    private $sign;

    public static setKey($key) {
        self::$key = $key;
    }

    public static function makeSign($param) {
        return hash_hmac('sha1', $param, self::$key);
    }

    private function validate() {
        $validSign = $this->generateSignature();

        if ($validSign === FALSE) {
            return false;
        }

        if ($validSign !== $this->sign) {
            return false;
        }

        return true;
    }

    private function __construct($param, $signature) {
        $this->param = $param;
        $this->signature = $signature;
    }

    public function get() {
        $this->validate();
        return $this->param;
    }
}

// sample out
$sign = SignedParam::makeSign($out);

// sample in
$in = new SignedParam($sign, $param)->get();