The Attack of the Clones Against Proof-of-Authority

Parinya Ekparinya (University of Sydney), Vincent Gramoli (University of Sydney and CSIRO-Data61), Guillaume Jourjon (CSIRO-Data61)

The vulnerability of traditional blockchains have been demonstrated at multiple occasions.
Various companies are now moving towards Proof-of-Authority (PoA) blockchains with more conventional Byzantine fault tolerance, where a known set of $n$ permissioned sealers among which no more than $t$ are Byzantine seal blocks that include user transactions. Despite their wide adoption, these protocols were not proved correct.

In this paper, we present the Cloning Attack against the two mostly deployed PoA implementations of Ethereum, namely Aura and Clique. The Cloning Attack consists in one sealer cloning its key-value pair into two distinct Ethereum instances that communicate with distinct groups of sealers.
To identify their vulnerabilities, we first specified the corresponding algorithms. We then infer the topology of the largest PoA network, POA Core, through active measurement. We deploy one testnet for each protocol and demonstrate the success of the attack with only one byzantine sealer. Finally, we propose counter-measures that prevent an adversary from double spending.