op-challenger

op-challenger •

A modular op-stack challenge agent for attestation (fault and validity soon™) dispute games written in golang. Please note this is a proof of concept not intended for production use. The authors of this repository expressely recommond following the rust-based op-challenger for performance.

Quickstart

First, clone the Optimism Monorepo and set the MONOREPO_DIR environment variable to the path of that directory in a .env file as shown in .env.example.

Then, you can simply run make, which will compile all solidity + golang sources, bring up the Optimism devnet while also deploying the mock dispute game contracts, and then run the op-challenger.

Alternatively, you can build the op-challenger binary locally using the pre-configured makefile target by running make build, and then running ./op-challenger --help to see the available options.

In the future, we intend to support downloading the op-challenger binary from challenger.refcell.org using curl -s https://challenger.refcell.org | sh

Usage

op-challenger is configurable via command line flags and environment variables. The help menu shows the available config options and can be accessed by running ./op-challenger --help.

Note that there are many global options, but the most important ones are:

• OP_CHALLENGER_L1_ETH_RPC: An L1 Ethereum RPC URL
• OP_CHALLENGER_ROLLUP_RPC: A Rollup Node RPC URL
• OP_CHALLENGER_L2OO_ADDRESS: The L2OutputOracle Contract Address
• OP_CHALLENGER_DGF_ADDRESS: Dispute Game Factory Contract Address
• OP_CHALLENGER_PRIVATE_KEY: The Private Key of the account that will be used to send challenge transactions
• OP_CHALLENGER_L2_CHAIN_ID: The chain id of the L2 network

Here is a reduced output from running ./op-challenger --help:

NAME:
   op-challenger - Modular Challenger Agent

USAGE:
   main [global options] command [command options] [arguments...]

VERSION:
   1.0.0

DESCRIPTION:
   A modular op-stack challenge agent for output dispute games written in golang.

COMMANDS:
   help, h  Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --l1-eth-rpc value                      HTTP provider URL for L1. [$OP_CHALLENGER_L1_ETH_RPC]
   --rollup-rpc value                      HTTP provider URL for the rollup node. [$OP_CHALLENGER_ROLLUP_RPC]
   --l2oo-address value                    Address of the L2OutputOracle contract. [$OP_CHALLENGER_L2OO_ADDRESS]
   --dgf-address value                     Address of the DisputeGameFactory contract. [$OP_CHALLENGER_DGF_ADDRESS]
   --private-key value                     The private key to use with the service. Must not be used with mnemonic. [$OP_CHALLENGER_PRIVATE_KEY]
   ...
   --help, -h                              show help
   --version, -v                           print the version

Inner Workings

The op-challenger is a challenge agent for the output dispute game. It is responsible for challenging output roots.

This implementation is loosely based off the op-proposer, a proposer agent that is responsible for proposing new outputs to the L2OutputOracle. And this should make sense; where the op-proposer posts outputs to the L2OutputOracle, the op-challenger validates these outputs and disputes them if invalid. The primary functional difference the op-challenger must implement is the ability to challenge invalid outputs.

The naive challenge agent will be an attestation challenger which is a permissioned set of actors running the op-challenger. Below we illustrate how the challenger agent interacts with the op-stack's permissionless output proposal system.

The next iteration of the challenge agent will use fault proofs to challenge invalid outputs. This will involve a more complex dispute game which will allow for permissionless challengers by attaching bonds to each level of the dispute game. A future iteration could allow for validity (zero-knowledge) proofs.

Contributing

See CONTRIBUTING.md

License

MIT, forever and always.

Acknowledgements

• op-challenger: a rust challenge agent 🦀
• optimism: the optimism monorepo 🚀
• op-stack: the op-stack 🥳