  Bitcoin uses blockchain technology to maintain transactions order and
provides probabilistic guarantee to prevent double-spending, assuming that an
attacker's computational power does not exceed %50 of the network power. In
this paper, we design a novel bribery attack and show that this guarantee can
be hugely undermined. Miners are assumed to be rational in this setup and they
are given incentives that are dynamically calculated. In this attack, the
adversary misuses the Bitcoin protocol to bribe miners and maximize their
gained advantage. We will reformulate the bribery attack to propose a general
mathematical foundation upon which we build multiple strategies. We show that,
unlike Whale Attack, these strategies are practical. If the rationality
assumption holds, this shows how vulnerable blockchain-based systems like
Bitcoin are. We suggest a soft fork on Bitcoin to fix this issue at the end.
