Trust-less and Efficient Bridges between PoS Blockchains via Random Sampling, Bhargav Bhatt

Talk by Bhargav Bhatt (Web3 Foundation)
Abstract:
We introduce “Random Sampling”, a novel technique for on-chain light-clients to efficiently follow the finality of a PoS blockchain. Essentially, our technique draws randomness (e.g. RANDAO in Ethereum) from the target chain to verify the signatures of only a small subset of validators subsampled from the source chain. We also analyse the security of the bridge from a crypto-economic perspective. This includes an overview of interesting concurrency issues in initial designs, and fixes which rely on dynamically increasing the security parameter only in case of an attack. Our work does not rely on fancy crypto and is comparable to SNARK based techniques in terms of gas costs (if the target chain is Ethereum). Our technique is already implemented in the Polkadot to Ethereum bridge which is scheduled to go live soon.