Replay Attacks and Defenses Against Cross-shard Consensus in Sharded Distributed Ledgers

Understand

We present a family of replay attacks against sharded distributed ledgers, that target cross-shard consensus protocols, such as the recently proposed Chainspace and Omniledger.

• They allow an attacker, with network access only, to double-spend or lock resources with minimal efforts.
• The attacker can act independently without colluding with any nodes, and succeed even if all nodes are honest; most of the attacks can also exhibit themselves as faults under periods of asynchrony.
• These attacks are effective against both shard-led and client-led cross-shard consensus approaches.