为cookie创建验证密钥

Question

I've working on secure cookies for all users and a fast way to verify them.

This is what i come up with:

When you register a user a salt is generated into the database for each user.

When you log in set these two cookies:

$_COOKIE["key"] and $_COOKIE["user"]

$_COOKIE["user"] is the ID of the user that logged in.

The $_COOKIE["key"] is set like this: sha1(sha1($id).sha1($salt));

and then to verify the cookies i created this function:

public function check_cookie(){


    //CHECK IF THE COOKIE IS MATCHING THE HASHKEY AND IF USER IS CONTAINING NUMBERS
    if(sha1(sha1($_COOKIE["user"]).sha1($salt)) != $_COOKIE["key"] || 
!is_numeric($_COOKIE["user"])){

        //REMOVE COOKIES 
        setcookie('user', null, -1);
        setcookie('key', null, -1);

        return FALSE;

    } else {

        return TRUE;

    }

}

Is this a secure way to do it? Do you see any fault in this way of structure?

Thanks in advance!