Please note that some of this will be outdated. This also does not include layerzero, wormhole, synapse, abacus, NEAR’s rainbow bridge, and Ren, plus countless multisig bridges.
\nThis is a brief intro to Axelar, Celer, Gravity, and Nomad.
\nAxelar network is built from the ground up using Cosmos SDK to interoperate between Cosmos chains, EVM chains, Bitcoin, and other PoS and PoW chains. Satellite is the cross-chain asset transfer app built on top of the network and has amassed over $37m TVL and 100k cross-chain transactions since launching in February. It has also recently become the official canonical bridge for Osmosis and plans to further expand its reach into the Cosmos and EVM ecosystem.
\nSatellite currently supports Avalanche, Polygon, Terra, Osmosis, Moonbeam, Fantom, Ethereum and Cosmos Hub with plans to support all major EVM chains over the next couple months.
\nSatellite connects all Cosmos chains via IBC and its GCP protocol with multiple ecosystems.\nIt’s built on top of Axelar’s “decentralized overlay network” that connects different blockchain stacks. Axelar serves as the translation layer that allows Cosmos assets to flow freely to all Axelar-interconnected networks and back. It is permissionless, meaning that anyone can join, submit transactions, relay, and validate.
\nAxelar has been audited by Ackeeblockchain, Cure53, NCC, Oak Security, Commonprefix labs and independent researchers and is also dedicating at least 5% of AXL supply to an insurance fund/program that will help recuperate any stolen funds to ensure the safety of its users.
\nAxelar believes that bridging solutions should be at least as secure as the chains being bridged. Axelar’s solution is having a Cosmos chain, one with a similar validator set to other chains. Additionally, they are heavily invested in securing their smart contracts and in applying cutting-edge cryptography.
\nThe Axelar network isolates functionalities in modules at the Cosmos SDK level, e.g., one module for bitcoin, another for EVM chains, another for IBC transfers, etc.
\nEach module handles the respective transactions from source and destination chains and are isolated from each other and messages can only be passed through a router module. If there is an issue with one or all chains, a special transfer command that can be supplied by the governance multisig can pause the router module.
\nThere is also minimal reliance on smart contracts and are only used for key-rotations and mint/burn operations.
\nThe mint/burn contracts can also be freezed in case of a compromise and have a rate-limit functionality that allows to minimize how much funds can be stolen in case of an attack. This is not enabled on the mainnet at the moment, but can be considered along with other “access control” policies to minimize attacks.
\nThere will also be an insurance fund/program of at least 5% of the AXL supply to compensate users in case of stolen funds. Axelar has also been audited by Ackeeblockchain, Cure53, NCC, Oak Security, Commonprefix labs and independent researchers and gone through a dozen audits.
\nAxelar currently has a set fee on each transfer that covers gas costs on source + destination chain. Axelar foundation subsidizes any increase in the destination gas cost if need be and is also considering subsiding fees further from its treasury.
\nTransactions are also batched, reducing the gas costs for the users significantly. Axelar also has active implementation of threshold signatures that can be used to replace individual validator signatures and further save gas costs. While not currently deployed in EVM contracts, this is just one of the many code-level gas optimizations that Axelar will ship in the future.
\nUsers only pay the fee in the asset they transfer on the source chain, and all other fees (relaying / intermediary / destination chains) are covered by services around the network.
\nApp:\nhttps://satellite.axelar.network/
\nCeler Network is a multi-chain operating system built with Cosmos SDK. Celer released the world’s first EVM-supported inter-chain message SDK. and has a track record of no hacks for any product since Celer originated in 2018.
\nCeler cBridge is a token bridge application built on top of Celer that supports 45 different tokens across 21 different blockchains and layer-2 rollups. cBridge has 400MTVLandhasprocessedmorethan4B of cross-chain volume for 105K unique users with a daily volume of 50M−60M across 21 different blockchains.
\ncBridge comes with two security models that every user can choose between, the Cosmos-consensus security model and an optimistic-rollup-style delay buffer security model. The consensus model is security that of a validator-based bridge, while the optimistic rollup style also has a delay buffer to allow an independent watchtower service to double check the message.
\nUsers have single-click UX with fast confirmation of the bridge between source and destination chains and with 2,500-3,500 daily active users comfortable with using Celer Network.
\nCosmos-consensus Security Model:\nCeler SGN is running as a Cosmos chain with the same level of liveness assumption which is very high like other Cosmos chains. Celer provides an L1-blockchain level security like Cosmos or Polygon as a Proof-of-Stake chain built on Tendermint with CELR as the staking asset. If a validator acts maliciously, their CELR will be slashed.
\nOptimistic-rollup-style delay buffer Security Model:\nInter-chain dApps can maintain full security with an optimistic-style delay buffer. Instead of instantly processing a message through the consensus model, one can inject a mandatory delay buffer and run an independent watchtower service to double-validate the message on the source chain. If the watchtower service detects any inconsistency, it can prevent the message from being processed before the delay expires.
\nFor transactions larger than a certain amount, two-transactions are needed to make the bridge happen: a “commit” transaction that will trigger the time buffer and then after the time buffer, a “confirm” transaction. The watchtower system also monitors the bridge for small transactions as well to detect and prevent any unexpected smart contract bugs. There is also rate-limiting for token bridging as the last-resort to worst-case scenario.
\nIn addition, Celer cBridge smart contract has been heavily audited and also has a $2M ImmuneFi bug bounty. Celer Network also has a track record since 2018 of no hacking event happening for any product they have built.
\nCosts:\ncBridge charges the gas fee on the destination chain to cover the operation costs of validators. The fee is not related to the size of the transaction, unlike many other bridging solutions.
\nCeler also has no plans to change the fee structure and remains committed to supporting inter-chain apps where IBC is not available. Unlike other bridges that plan on changing to percentage-based fees later, Celer will only charge a flat fee based on the size of the message passed to provide revenue for validators.
\nThere are also no platform fees charged by the Celer Network for token asset bridging.
\nhttps://cbridge.celer.network/#/transfer
\nThe Gravity Bridge blockchain is the trustless, neutral bridge between Ethereum and the Cosmos ecosystem. The principal focus of the Gravity community is on providing the most effective and secure bridge possible, instead of a DeFi application on the local chain.
\nGravity Bridge protocol focuses on creating a simple bridge design that focuses on providing better security by eliminating design complexity and using non-upgradeable contracts which have been audited by Certick, Least Authority and Cod4rena.
\nThe Gravity Bridge protocol provides strong censorship resistance guarantees and the bridge will remain live as long as the chain remains live, i.e. with more than 2/3 of validators active.
\nCurrently supports Ethereum and has plans to support additional EVM chains before the end of 2022.
\nWhile there is not currently a set-aside for an insurance fund, one could easily be set aside from the community pool which contains 50% of $GRAV token distribution which could also contain a collection of assets.
\nGravity Bridge is trustless, decentralized and highly efficient and offers the closest approximation of IBC security possible. It is highly decentralized with all funds directly controlled by validators with slashing to deter validators from acting in bad faith.
\nThe Gravity Bridge design means that the only way to attack the bridge is to go through the validators themselves. This results in a trustless bridge that costs less to operate than a custodial one. It is not possible for a validator to avoid signing a specific transaction or for a relayer to avoid relaying it. Anyone can submit evidence of a signature over a non-protocol message to slash a validator which makes it extremely difficult for validators to steal funds.
\nThe Gravity Bridge, like all bridges, has two components. A Solidity contract on Ethereum and a CosmosSDK module on the Gravity Bridge blockchain.
\nThe solidity contract that holds funds on Ethereum is merely 580 lines of code, which makes it compact and easy to review. It has been audited by three independent teams (Certik, Least Authority, and Code4rena), and it is not upgradable. It requires no trusted parties and can be temporarily paused by governance vote in case of a possible security breach. As a final layer of protection the Gravity Bridge blockchain performs a series of integrity checks that will halt the chain on any unexpected behavior.
\nWhile there’s nothing set for an insurance fund at the moment, the $GRAV token holders can choose to use some funds from the large community pool to help recuperate stolen funds.
\nRobust relaying reward systems combined with reduced gas costs creates extremely fast & reliable transfers with a decentralized, self-funded, relayer community
\nGravity Bridge batches withdraw transactions. This works like a rollup on Ethereum. Executing many transactions in a single shared context is far more efficient than doing so individually. This process provides huge efficiency gains, up to 96% reduction in gas cost.
\nOnce bridge traffic has matured, tx fees could be enabled by the community to sustain the community pool. These tx fees are payable in a wide variety of tokens, not solely in GRAV. Other mechanisms, like a portion of the inflation, could be used to fund the community pool.
\nNomad is an interoperability protocol for generalized message passing. At its core, it uses an optimistic mechanism with fraud proofs to reduce the overhead of sending messages between chains and requiring 100+ validators. Nomad is designed to be non-custodial, trust-minimized and will be permissionless and decentralized in the future. With their unique watcher system, they forgo the need of 100+ validators and need only 1 good faith watcher to prevent fraudulent transactions.
\nUnlike validator-based bridges, Nomad channels only require one “validator” and as a result, are easy to scale and deploy rapidly. It optimizes for high security, low cost, with the trade-off of mild latency to ensure fraud proofs can be confirmed on-chain.
\nNomad is already running in production on Ethereum and Moonbeam, and has 70M+TVLincontracts,andover300M in total volume bridged. By the middle of Q2, Nomad will also support Arbitrum, Optimism, Polygon, BSC, Avalanche, and Fantom.
\nEvmos will officially use Nomad and Connext as its bridging solutions, with Nomad as the settlement layer and Connext as the liquidity layer. Connext and Nomad have a deep partnership that enables the modular interoperability stack.
\nNomad is composed of multiple agents — an updater, relayers, processors, and watchers. The most important is the updater, whose job it is to “validate” or update new roots.
\nThe updater is the sole “validator” in the system, and Nomad prevents liveness issues by downtime slashing + rotation, similar to that of a validator system. Relayers are like IBC relayers, and processors simply prove inclusion of messages on replicas — these are both permissionless roles. The watchers observe updaters to ensure that they are behaving correctly, and flag fraud if observed. Watchers allow Nomad to have a trust model where there only needs to be one honest actor, rather than a majority.
\nCurrently, the bridge is running in a permissioned environment with the core team running all updaters and watchers, but agents will become decentralized as Nomad continues to expand into the market.
\nNomad has partnered closely with Connext to provide a “fast liquidity” option. Connext uses liquidity pools to allow instant bridging whenever enough liquidity is available. If Connext’s liquidity network can’t offer sufficient liquidity, Nomad will default to its locking-and-minting layer, with the 30 minute dispute window.
\nNomad has been audited back in October 2021 and is currently in the middle of a Quantstamp audit — with no flagged issues thus far.
\nNomad doesn’t have to pay 100+ validators to maintain the bridge and therefore requires minimal fees. Users will only need to incur network fees of the underlying chains.
\nThe off-chain agents are currently run by the Nomad core team who are subsidizing fees. As Nomad progressively decentralizes agent operations, new actors will probably begin to charge fees in exchange for relaying transactions across chains.
\nThe only cost Nomad charges is the underlying gas fees to submit transactions on various networks plus any premium agents add on top. For fast chains with lower gas fees, the cost should be in the order of cents to a couple dollars.
\nThere are no platform “toll” fees on Nomad, and they’re making an effort to reduce gas and network fees by implementing optimizations around enqueuing messages and processing.
\nUsers can use Metamask to send their transaction, and after a pre-defined latency for the chain pair (~30 mins for Ethereum), will receive their tokens on the destination chain. Nomad subsidizes the relaying and processing costs, and only requires users to pay network fees with no additional cost.
\n