The Balance Attack Against Proof-Of-Work Blockchains: The R3 Testbed as an Example
This exposes a vulnerability in proof-of-work protocols for consortium blockchains, which is an incremental but practical security concern.
The authors identified a new 'Balance attack' on proof-of-work blockchains by delaying communications between subgroups with balanced mining power, showing that a single machine can attack the R3 consortium in 20 minutes.
In this paper, we identify a new form of attack, called the Balance attack, against proof-of-work blockchain systems. The novelty of this attack consists of delaying network communications between multiple subgroups of nodes with balanced mining power. Our theoretical analysis captures the precise tradeoff between the network delay and the mining power of the attacker needed to double spend in Ethereum with high probability. We quantify our probabilistic analysis with statistics taken from the R3 consortium, and show that a single machine needs 20 minutes to attack the consortium. Finally, we run an Ethereum private chain in a distributed system with similar settings as R3 to demonstrate the feasibility of the approach, and discuss the application of the Balance attack to Bitcoin. Our results clearly confirm that main proof-of-work blockchain protocols can be badly suited for consortium blockchains.