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Namada Ethereum Bridge

This repository contains a set of smart contracts that enable the exchange of tokens between the Namada chain and ERC20 Ethereum tokens. The design of the bridge is inspired by the Cosmos Gravity Bridge.

Design overview

The smart contracts are designed in a generic way, such that they may be plugged to an arbitrary BFT consensus chain, with >2/3 of signatures by voting power (i.e. stake, if it is a PoS secured chain) over some bridge protocol message.

Value transferred to the native chain is escrowed in a vault abstraction, which enables other contracts to be upgraded without moving value around. When ERC20 tokens are transferred back to Ethereum, value is released from escrow into the destination accounts. As for tokens of the native chain, these are minted on Ethereum, when transferred over, and burned, when transferred back.

Transfers to the native chain may be unordered from the point of view of Ethereum. However, transfers to Ethereum, originating from the native chain, must be ordered by a monotonically increasing sequence number. The nonce is signed together with the root of a merkle tree containing transfers made by users in the native chain. This merkle tree is dubbed the Bridge pool, as it functions as a mempool of sorts. Existence proofs of a transfer in the Bridge pool must be provided, for a transfer to be validated.

To decrease gas costs on Ethereum, transfers may be batched together. It is expected that wallet implementations will facilitate the batching process, and warn users that their transfers will not take any effect until they have been flushed from the queue of pending transfers.

Features

  • Handle multiple ERC20 token transfers.
  • Batched transfers.
  • Issue native namada token on Ethereum.
  • Audit.

Smart contracts

The smart contracts used to operate the Namada bridge on Ethereum are:

  • Bridge.sol: Authorizes tokens transfers to/from Namada.
  • Proxy.sol: Keeps track of the existing contract addresses and can be queries by other smart contracts.
  • Vault.sol: Secures escrowed ERC20 tokens.
  • Token.sol: Corresponds to the native token of the chain that is being bridged to.
  • TestERC20.sol: Test token used solely in tests.

Development

Development is done with foundry, aided by just. All available commands can be queried with just --list.

Building the Ethereum smart contracts

$ just build

Running a development Ethereum node

$ just anvil

Deploying the smart contracts to the development node

$ just anvil-deploy <bridge-validator-set> <governance-validator-set>

Example JSON validator sets can be found inside of the scripts directory.

Broadcast a TestERC20 transaction to the development node

$ just anvil-allow <transfer-amount>
$ just anvil-transfer <target-namada-addr> <transfer-amount>

Start a development Solidity REPL

$ just