Celer IM — A Deep Dive
All you need to know about Celer IM
Introduction
We recently published a 10,000-word document comparing seven of the most well-known arbitrary messaging bridges (AMBs). Today, we’re expanding the document by adding a new AMB to the mix — Celer IM.
This article will explore the design, security, and trust assumptions of Celer IM, an arbitrary messaging bridge (AMB) enabling users and developers to transfer both simple messages and complex data across chains.
You can also listen to our conversation with Mo Dong, the co-founder of Celer Network, who recently spent an hour explaining the ins and outs of Celer IM with us on Twitter Spaces.
Here, we will cover the following:
- Celer IM — An Overview
- How It Works — Transaction Lifecycle
- Security features
- Trust Assumptions
- Community & Resources
Let’s dive in!
Overview
Celer Inter-chain Message (Celer IM) is designed as a “plug and play” cross-chain composability solution for building cross-chain dApps to promote efficient liquidity utilization, coherent application logic, and shared state across tens of chains. The Celer IM architecture is powered by a combination of on-chain smart contracts that receive and send messages and the Celer State Guardian Network, a proof-of-stake blockchain built on Tendermint specializing in authenticating cross-chain messages. cBridge, a fungible token and NFT bridging application is built with this architecture as a “built-in” cross-chain dApp. With the combination, Celer IM enables a robust set of use cases for dApps like cross-chain DEXes, yield aggregators, lending protocols, multi-chain NFTs, and more. As of August 2022, Celer IM supports arbitrary message passing and cross-chain contract calls across Ethereum, BNB Chain, Polygon, Fantom, Avalanche, Arbitrum, Moonriver, Optimism, and Aurora.
Some of CelerIM’s best features include:
- Plug and Play — New and existing dApps can integrate Celer IM through a simple plug-in contract that often requires no code modifications to deployed code.
- Support for all types of chains — Celer IM enables the transfer of arbitrary data like contract calls, messages, tokens, NFTs, and data between L1s, sidechains, and L2s.
- Single UX — Celer IM allows multiple functions like bridge and swap to be performed within a single user experience. As a result, the users have to go through fewer clicks, significantly improving a dApp’s UX.
- Transaction Flexibility — dApps can send a message and fungible tokens in one transaction. However, if the need arises, dApps utilizing Celer IM can also just pass a message across chains.
- Security of Celer– Cross-chain dApps built on top of Celer can choose two different security models with different tradeoffs on delay. By default, inter-chain dApps rely on the security of the State Guardian Network (Cosmos PoS-based chain) by processing messages routed from another chain without delay. Developers can also choose to use an optimistic rollup-like security model with additional cross-chain communication delay. .
- Potential Bridge Expansion — While Celer IM was initially built using cBridge as its go-to asset bridge for passing fungible tokens across chains, the protocol has plans to add other asset bridges to its repertoire.
Additionally, Celer IM has developed tremendous network effects:
- cBridge has processed $10.4 billion in cross-chain transactions and has $173.19 million in total value locked into its protocol, which supports 25 bridges.
- CELR is a top 300 token with a market capitalization of roughly $100 million.
- Celer IM launched with nine partners, including SynFutures, Ooki, and Rubic.
How it Works
As mentioned above, Celer IM utilizes the SGN’s ability to validate cross-chain messages emitted from one chain and pass them on to another chain. The entire process takes roughly eight steps and is bookended by a user initiating an action on the source chain and receiving a token or message on the destination chain. Composing with Celer cBridge, Celer IM’s architecture enables both token and arbitrary data to be passed together (or separately) in one transaction, unlocking tons of potential for developers to build on top of.
This is what it looks like at a high level:
Let’s break this down. First, for clarification purposes, the blue lines above show how token transfers flow through the Celer IM architecture. The green lines show arbitrary data flowing through Celer IM.
The transaction flow can be grouped into the following actions:
- A user interacts with a dApp utilizing the Celer IM plug-in and performs an action such as attempting to swap token A on Chain X for token B on Chain Y.
- The Celer IM plug-in contract splits the user request into two parts: token information sent to cBridge and message information sent to the “MessageBus.”
- From there, the MessageBus and cBridge relay information to the SGN, which validates the transaction via a signature after both the message and token transfer are confirmed to have occurred on the destination chain.
- The executor, an open node on the destination chain, accepts the request from the SGN and executes the final logic on the destination chain.
- After this, the submitted information (both token and message) is called to the destination application, and, for example, the user receives token B on Chain Y.
Notably, Celer IM can also facilitate the transfer of data without moving a fungible token. The flow looks like this:
Security
Celer IM offers the following security features:
- SGN — The State Guardian Network routes messages and cross-chain fund transfers for Celer IM. The network is a proof-of-stake network built on Tendermint secured via CELR staking. With SGN, the network is secured via staking and slashing mechanisms similar to those seen on Cosmos, Ethereum 2.0, and Polygon. As of late August 2022, SGN has 21 validators staking roughly $42 million worth of CELR to the network, with entities such as Binance and Everstake running validators.
- Optimistic Fallback: Celer offers dApps a second security model that should work securely even under the worst-case scenario (two-thirds of the validators behave maliciously). Instead of instantly confirming messages routed through the SGN, a message must be committed into a “quarantine” zone for a limited time before the message can be confirmed for the destination application. During this delay, dApps can implement (or commission an SGN node as) a guardian service to double-authenticate messages.
- Audits and bounty system — PeckShield and SlowMist have audited Celer IM. Furthermore, cBridge has one of the more extensive bounty programs in the space via a $2 million offer on Immunefi.
Trust Assumptions
Celer makes the following trust assumptions:
- External Verification under PoS model — Celer IM uses a validator set with 21 validators to execute transactions. A message must be signed by ⅔ of staked value. Based on current staking numbers, it would only take ⅓ (7 entities) to maliciously conspire to leave the chain exposed to harmful activity. Celer IM assumes that the slashing mechanics of CELR and the reputational pressure that comes with validating a public blockchain will lead to validators acting honestly.
- Trust-any Under Optimistic Rollup Model — When operating under the optimistic fallback model, the security assumption is that as long as there is still one application guardian that stays honest and functional, malicious cross-chain messages will not be processed.
- Structural Integrity of cBridge and SGN — Celer IM is built on the assumption that both the SGN and cBridge consistently stay live, do not get exploited, and, most importantly, work as expected.
- CELR Stakers and Value — Celer IM leans heavily upon CELR through staking. Furthermore, users of Celer IM have to pay fees in CELR to the SGN for its services in reaching cross-chain consensus. If the CELR token drastically fell in price, the security of the SGN would most likely also fall.
- Celer IM Plug-in — One of the main conveniences of Celer IM is its “plug and play” nature. However, as with all smart contract native entities, if the Celer IM smart contracts that dApps use to pass messages across chains fail, the consequences could be dire.
Closing Thoughts
Celer IM aims to provide secure infrastructure for developers to build cross-chain dApp. We are super excited by what the team is building and can’t wait to see what the AMB structure unlocks for the crypto space.
And, of course, LI.FI is thankful for all the feedback and cooperation from the Celer IM team in creating this doc.
There is a whole ecosystem of AMBs, enabling complex cross-chain functionality for dApps. If you’re interested in learning more about the different types of AMBs, check out LI.FI’s comparison framework, which enables readers to quickly assess the pros and cons of an AMB.
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