There's no way (if there's no offline part) At least I spent a few minutes here and there since yesterday thinking how it could be secured. Any method I though

There's no way (if there's no offline part) At least I spent a few minutes here and there since yesterday thinking how it could be secured. Any method I thought was quickly demolished by a few attacks that would work. But I am open to be corrected! If anyone thought they could have solved this problem, please reply :)