A guide to cross-chain bridges
Introducing Toshokan, a community-first blog for Sushi

Introducing Toshokan, a community-first blog for Sushi

Today we're excited to introduce Toshokan (図書館 Japanese word for library), our new blog that will help keep our community informed about the latest happenings at Sushi.

7 min read

A guide to cross-chain bridges

Interoperability is the key to mainstream adoption. Learn and understand how the major bridges in the space work and the essential concepts behind them.
A guide to cross-chain bridges

There are more than 125 blockchains (Layer 1 and 2), and since they are all separate, they are not interoperable. Each one is limited within its domain, with its advantages and disadvantages. The major downside of these chains is that they cannot directly interact with each other. This lack of communication between the chains affects the users and the space. With cross-chain bridges, it enables token transfers, smart contracts, and data exchange between different blockchains. Bridges (a type of settlement) do not particularly belong to blockchain and can exist as separate networks (middle chains). As we have an extensive range of blockchains and a comprehensive range of bridging protocols, we can help you connect to the right one for your needs.

You can find most of them here:

All blockchain bridges aggregator

Bridges can be trusted (centralized) or trust-less (decentralized to some degree). Most use lock and mint mechanics, while some act as a messaging system (Layer Zero). They can help you transfer an asset from one chain to another or other chains. In addition, they can let you move tokens between chains or multiple chains. In the same way, each blockchain has its strengths and weaknesses; speed, security, and price are just some of the factors a user must consider when deciding which bridge to use.

There are well more than 100 bridges, but here are some of the popular ones:

Hop Exchange
A protocol for sending tokens across rollups and their shared layer-1 network in a quick and trustless manner.

Hop is a scalable rollup-to-rollup general token bridge that enables users to send tokens from one rollup or sidechain to another almost immediately without having to wait for the networks challenge period.

Celer - https://cbridge.celer.network/

The Best Crypto & Binance Bridge | cBridge
cBridge is a multi-chain, cross-layer asset bridge offering instant transfer with the most number of chains, lowest fee and zero trust.

Celer cBridge is a multi-chain network that enables instant, low-cost and ANY-to-ANY value transfers within and across different layer-1 blockchains and different layer-2 scaling solutions on top, such as Optimistic Rollup, ZK Rollup and sidechains.

Multichain - Cross-Chain Router Protocol
Multichain is a cross-chain router protocol; an infrustructure for multi-chain ecosystem, envisioned to become the ultimate router for Web 3. Non-custodial+MPC, Non Slippage Swap, Multichain Router

The Multichain network is made up of what are called SMPC nodes. These are standalone entities from blockchains that work together to sign transactions., but a group of them must do so together and they each only ever know part of the key to make this happen. are run by different organizations, institutions and individuals and they are incentivized to perform their functions properly.

Connext (previously xpolinate) - https://bridge.connext.network/

Connext | Cross-Chain Transfer
Transfer token between chains using NXTP

Connext powers fast, trust-minimized communication between blockchains. You can use Connext to send transactions of value or calldata across chains and/or rollups. Unlike most other interoperability systems, Connext enables this without introducing any new trust assumptions or external validators.

Across is the fastest, cheapest and most secure cross-chain bridge.

Across is an optimistic cross-chain bridge protocol that allows users to execute transactions between chains nearly instantaneously. This is accomplished by using an optimistic oracle, bonded relayers, and single-sided liquidity pools.

A user that would like to move funds from chain A to chain B deposits funds into a "deposit box" on chain A with instructions about where they would like their funds to wind up and the fee that they are willing to pay. Relayers view these deposits and, once they have verified that the details of the deposit are correct, immediately provide funds to the user on chain B. After the relayer has performed the relay, a proof of that relay and the validity of the original deposit is submitted to the Optimistic Oracle (OO) and the relayer is reimbursed once this information has been verified by the OO.

Bridge ETH from Ethereum Mainnet to Polygon Mainnet.
Bridge ETH from Ethereum Mainnet to Polygon Mainnet. Cheapest and fastest bridge from ethereum to Polygon Mainnet

The Umbria Narni Bridge uses a novel liquidity-provision protocol, to speed up, and lower the cost of cross-chain bridging. The bridge facilitates cross-chain migration of assets by holding multiple assets on multiple chains, simultaneously, in liquidity pools. Unlike traditional cross-chain bridges, the Umbria Narni bridge is able to facilitate cross-chain transactions by receiving assets on one chain, and giving the respective asset on the destination chain. The Umbria Narni bridge is different to other cross-chain bridges, because it does not rely on validator smart contracts, which can dramatically slow the bridging process. By removing the necessity for such validation, the Umbria Narni bridge can complete cross-chain transactions with an order of magnitude cheaper fees.

Polygon Web Wallet v2

Polygon bridge brings you a trust-less two-way transaction channel between Polygon and Ethereum blockchains by introducing the cross-chain bridge with Plasma and PoS security. With this, users can transfer tokens across blockchains without incurring third-party risks and market liquidity limitations.

Explore the Optimism Collective
Learn about OP and get started using applications on Optimism.

Optimism is designed so that users can send arbitrary messages between smart contracts on Optimism and Ethereum. This makes it possible to transfer assets, including ERC20 tokens, between the two networks. The exact mechanism by which this communication occurs differs depending on the direction in which messages are being sent.

Optimism uses this functionality in the Standard bridge to allow users to deposit assets (ERC20s and ETH) from Ethereum to Optimism and on also allow withdrawals of the same from Optimism back to Ethereum. See the developer documentation and examples on details on the inner workings of the Standard bridge.

Arbitrum Bridge
Arbitrum L1/L2 Token Bridge

The Arbitrum protocol's ability to pass messages between L1 and L2 can be leveraged to trustless-ly move assets from Ethereum to an Arbitrum chain and back. Any asset / asset type can in principle be bridged, including Ether, ERC20 tokens, ERC-721 tokens, etc.

The AB was designed to satisfy the following requirements:

Secure: the bridge must be audited and built with security-first technologies.
Cost Effective: the cost for bridging assets should be as low as possible.
Fast: the transaction should take the least amount of time possible.
Transparent: users should be informed of the transfer status at every step of the process.
Intuitive: users new to crypto asset transfers can easily understand the steps necessary to use the bridge.
Ecosystem-supportive: upon crossing the bridge, users should understand all of the capabilities of the Avalanche ecosystem and experience minimal friction in seizing opportunities.
Multi-chain: the bridge will support a growing number of blockchains in the future to center Avalanche as a core hub of DeFi.

Bridge aggregators

Bungee aggregates all your favourite bridges and gets you the cheapest and fastest routes to jump across chains!

Bungee at its core, is a bridge aggregator. It can be thought of as 1Inch, or Paraswap for cross-chain bridging.

Zapper - Your Home to Web3
A simple dashboard for web3. Easily track and visualize all your DeFi assets and liabilities in one simple interface.

Zapper’s recently relaunched in-app bridge, powered by Socket, finds the perfect bridging route between the chains supported by Zapper.

No matter how handy bridges are, many people view them with skepticism and see them as a possible point of failure. Therefore, always do your own research and proceed with caution. For example, bridges aren't immune to exploits - some of the biggest exploits in the space happened to be of bridging protocols. DYOR! STAY SAFE!

P.S. Remember that a token can be bridged to a blockchain through two different bridges, and the two bridges may have different versions of the token on that blockchain. These versions may not be compatible with each other, so be sure to double-check the details of your transaction before you send it off to the blockchain using bridges.