pos-consensus-proof

Generate consensus proof for Polygon PoS chain using SP1.

Warning

This work is not audited. Please use at your own risk.

Background

Polygon PoS contains 2 layers — bor (execution layer based on geth/erigon) and heimdall (consensus layer based on tendermint). Polygon is also building AggLayer, which expects each chain to generate a ZK proof with different security assumptions. A full execution proof is practically infeasible with a 2s block time for PoS. Hence, as an excercise to plug PoS into AggLayer, we rely on consensus proofs.

Proving Consensus

Consensus proofs asserts that the majority (>2/3) of PoS validator set agree on a specific state of chain. This allows an external layer (e.g. AggLayer) to verify that the chain is operating honestly assuming the majority validator set is honest. To elaoborate a bit more, the specific state of chain here means a particular state of the execution layer. This is achieved using milestones, which is a also used for finality in PoS. Milestones are messages which are proposed in heimdall representing a range of bor blocks and is being voted upon and persisted. While there is more nuance to it, at a high level consensus proofs basically validates if majority of validators voted upon / signed a milestone message through signature verification.

Repository Overview

This repositories is organised into the following directories:

• consensus-proof: Contains the ZK circuit of verifying a milestone message and respective helper functions.
• operator: Implementation of an operator which assembles inputs used to generate the proof.
• common: Contains generic global types.
• contracts: The solidity contracts for on-chain verification and fetching validator set data.

Proof Generation

Make sure you've Rust and SP1 installed.

Contract Deployments

For proof generation (except the on-chain verification component), the StakeInfo contract acts as a proxy to fetch validator set and stake distribution from the respective L1 Stake Manager Contracts (already deployed for PoS mainnet and Amoy).

Existing deployments for StakeInfo:

• Ethereum Mainnet: 0x173ca2f40a37f62527713Bf72b085675A0D5e200
• Sepolia: 0x978D36Ed8c03EBF2d3b93b492aF8D37aD56ad1B5

Make a fresh deployment:

1. Make sure you have environment variables set corresponding to the chain you're deploying on.

   RPC=<rpc> # rpc endpoint of chain to be deployed on
   PK=<pk> # private key of account with funds to be used for deployment
   SM=<sm> # stake manager proxy address

2. Run the forge command to deploy inside the contracts directory.

   forge create --broadcast --rpc-url $RPC --private-key $PK --via-ir src/StakingInfo.sol:StakingInfo --constructor-args $SM
   

Using operator for proof generation

The operator service can be used for generating consensus proofs for any PoS chain given appropriate configurations are provided. Below are the steps to do the same.

1. Create an environment file using the example. Fill in all relevant details which will be used for assembling the inputs. It needs information about L1 (eth mainnet / sepolia), PoS endpoints (mainnet / amoy for heimdall and bor).

   cp .env.example .env

2. Make sure you're able to build the operator.

   cd operator
   cargo build

3. Run the operator service

   RUST_LOG=info cargo run --release -- <flags>

   Following flags are supported:
   • --prove: Generates an actual zk proof if set. If not, only executes the code with inputs.
   • --proof-type: Type of proof to be generated. Either compressed or plonk.
   • --skip-l1-block-validation: Skip validating the height of L1 block. Useful when testing against a fork.
4. Operator also has some helper commands.

   # To print the vkey
   RUST_LOG=info cargo run --release --bin vkey
   
   # To verify the proof generated
   RUST_LOG=info cargo run --release --bin verify

If you want to use the SP1 prover network, set the SP1_PROVER env variable to network and set the SP1_PRIVATE_KEY environment variable to your whitelisted private key. For more information, see the setup guide.

Acknowledgements

• SP1
• A PoC polygon-pos-light by Paul.