def crack1(self, rnum, snum, message, signsecret):
        """
        find privkey, given signsecret k, message m, signature (r,s)
        x= (s*k-m)/r
        """
        m = self.GFn.value(message)
        r = self.GFn.value(rnum)
        s = self.GFn.value(snum)
        k = self.GFn.value(signsecret)
        return (s * k - m) / r
find privkey, given signsecret k, message m, signature (r,s)
        x= (s*k-m)/r