The Longest-Chain Protocol Under Random Delays
This work addresses security degradation in blockchain consensus under realistic network conditions with sporadic large delays, offering a generalization of the synchronous model.
The paper analyzes the longest-chain blockchain protocol under random, independent, and identically distributed communication delays, providing safety and liveness guarantees with explicit bounds on failure probabilities that decay exponentially with the security parameter.
In the field of distributed consensus and blockchains, the synchronous communication model assumes that all messages between honest parties are delayed at most by a known constant $Δ$. Recent literature establishes that the longest-chain blockchain protocol is secure under the synchronous model. However, for a fixed mining rate, the security guarantees degrade with $Δ$. We analyze the performance of the longest-chain protocol under the assumption that the communication delays are random, independent, and identically distributed. This communication model allows for distributions with unbounded support and is a strict generalization of the synchronous model. We provide safety and liveness guarantees with simple, explicit bounds on the failure probabilities. These bounds hold for infinite-horizon executions and decay exponentially with the security parameter. In particular, we show that the longest-chain protocol has good security guarantees when delays are sporadically large and possibly unbounded, which is reflective of real-world network conditions.