Onomy Arc is a bridge extended from AltheaNet's Gravity Bridge that was designed to run on the Cosmos SDK blockchains like the Cosmos Hub focused on maximum design simplicity and efficiency. While initially a Cosmos <-> Ethereum bridge, Onomy has extended Gravity Bridge functionality with Arc by integrating additional chains to create a more inclusive cross-chain DeFi hub. Specifically, Arc pairs with the Onomy ecosystem of applications including the Onomy Exchange (hybrid orderbook + AMM DEX) and Onomy Access (multi-chain mobile wallet application) + more in future.

Additional functionality and integrations are audited by NCC Group.

Documentation

High level Explanation

Arc enables users to transfer tokens from an integrated chain to Onomy and back again by locking up tokens on integrated chain side, and minting equivalent tokens on the Onomy side. Arc is completely non-custodial, you only need to trust in the security of the Onomy chain itself - not some third party bridge administrators who could run off with your funds. The security of the Onomy chain, and thus Arc, is through the Onomy Validator Guild (OVG) which is comprised of a decentralized network of globally situated independent validator firms.

Code documentation

This documentation lives with the code it references and helps to understand the functions and data structures involved. This is useful if you are reviewing or working on the code.

• Solidity Ethereum contract documentation

• Go Cosmos module documentation

Specs

These specs cover specific areas of the bridge that a lot of thought went into. They explore the tradeoffs involved and decisions made.

• Slashing

• Batch creation

• Valset creation

Design docs

These are mid-level docs on the design overview page which go into the most detail on various topics relating to the bridge.

Integrated EVM Chains

Ethereum | Avalanche | Aurora | Polygon | Fantom | Neon | Moonbeam

Developer Guide

To contribute, refer to these guides.

• Environment setup

• Code structure

• Integration tests

• Security hotspots

Status

Arc is running on Onomy Testnet with the Ethereum bridge integrated. Audits have been completed by NCC Group. Additional bridges are ready to be integrated or are under development.

It is your responsibility to understand the financial, legal, and other risks of using this software. There is no guarantee of functionality or safety. You use the Arc bridge entirely at your own risk.

The design of Arc

• Trust in the integrity of Arc is anchored on the Onomy Network side. The signing of fraudulent validator set updates and transaction batches meant for the Ethereum contract, for example, is punished by slashing on the Cosmos chain.
• It is mandatory for validators to maintain a trusted Ethereum node. This removes all trust and game theory implications that usually arise from independent relayers, once again dramatically simplifying the design.

Key design Components

• A highly efficient way of mirroring Onomy validator voting onto Ethereum. The Arc solidity contract has validator set updates costing ~500,000 gas ($2 @ 20gwei). This was tested through Althea Net's Gravity Bridge with a snapshot of the Cosmos Hub validator set containing 125 validators. Verifying the votes of the validator set is the most expensive on chain operation Gravity has to perform. Our highly optimized Solidity code provides enormous cost savings. Existing bridges incur more than double the gas costs for signature sets as small as 8 signers.
• Transactions from Onomy to other chains are batched, batches have a base cost of ~500,000 gas ($2 @ 20gwei). Batches may contain arbitrary numbers of transactions within the limits of sends per block, allowing for costs to be heavily amortized on high volume bridges.

Operational parameters ensuring security

• There must be a validator set update made on the Ethereum contract by calling the updateValset method at least once every Cosmos unbonding period (usually 2 weeks). This is because if there has not been an update for longer than the unbonding period, the validator set stored by the Ethereum contract could contain validators who cannot be slashed for misbehavior.
• Onomy full nodes do not verify events coming from Ethereum. These events are accepted into the Cosmos state based purely on the signatures of the current validator set. It is possible for the validators with >2/3 of the stake to put events into the Cosmos state which never happened on Ethereum. In this case observers of both chains will need to "raise the alarm". We have built this functionality into the relayer.