We study the impact that Internet routing attacks (such as BGP hijacks) and malicious Internet Service Providers (ISP) can have on the Bitcoin cryptocurrency. Because of the extreme efficiency of Internet routing attacks and the centralization of the Bitcoin network in few networks worldwide, we show that the following two attacks are practically possible today:

Partition attack: Any ISP can partition the Bitcoin network by hijacking few IP prefixes.

Delay attack: Any ISP carrying traffic from and/or to a Bitcoin node can delay its block propagation by 20 minutes while staying completely under the radar.

The potential damage to Bitcoin is worrying. Among others, these attacks could reduce miner's revenue and render the network much more susceptible to double spending. These attacks could also prevent merchants, exchanges and other large entities that hold bitcoins from performing transactions.

The purpose of our research is to inform the Bitcoin users and miners as well as suggest long and short-term countermeasures. Check our paper for more details.