Bridging protocols today are not scalable. For a bridging protocol to be scalable, it must allow new networks to join easily and without restrictions. This requires the protocol to be permissionless; if any network can join without needing approval, the protocol can accommodate any number of networks.
The ideal experience should mirror that of ERC20 tokens on Uniswap. For example, if I have an ERC20 token, I can add it to Uniswap and ask liquidity providers to supply liquidity. Now, voilà, my token is available for anyone to trade. Bridging protocols should offer a similar experience. If I have a network, I should be able to add it to a bridging protocol, find a liquidity provider, and enable live bridging to and from my network immediately.
Currently, none of the existing solutions provide this experience. Let’s explore why.
Existing protocols fall into two main categories: Blockchain of Blockchains (e.g., Wormhole and Axelar) and Modular Security Protocols (e.g., LayerZero and Hyperlane).
Axelar and Wormhole act as “blockchains of blockchains.” They have their own set of validators connected to multiple other chains. These validators read and relay messages from source chains to their own chain and then pass information to the destination chain. The security of the relayed messages relies on validator consensus.
However, for a new network to join, it must convince the existing governance and validators to support it. This process is not permissionless and limits scalability. Any network wanting to join must undergo approval, preventing the protocol from effortlessly scaling to accommodate many new chains.
Modular Security Protocols like LayerZero and Hyperlane facilitate communication between networks through General Message Passing (GMP). By design, these systems are permissionless and open to all participants. However, when it comes to asset bridging, passing a message is not sufficient to transfer an asset. Asset transfers require liquidity and liquidity providers to facilitate trades, not just message passing.
Therefore, GMP solutions alone cannot transfer assets; an additional protocol handling both message passing and liquidity is necessary. Although the base layer of these protocols is designed to be permissionless—anyone can run Decentralized Validator Networks (DVNs)—the bridging protocols built on top do not inherit this permissionless nature because they delegate security decisions to the application layer.
Bridging protocols like Stargate (which operate at the application layer) must decide which DVNs to trust, creating a closed environment where they control access to networks. They must ensure the integrity and trustworthiness of DVNs, as there are no security guarantees at the protocol level. This vetting process contradicts the requirement for scalability, as it hinders the effortless addition of new networks. Consequently, despite the permissionless design of the base protocols, the necessity for security vetting at the application layer renders the overall system permissioned.
In summary, existing bridging protocols lack scalability due to their permissioned nature when onboarding new networks. A truly scalable bridging protocol should be permissionless—allowing any network to join without barriers, much like how tokens are added and traded on Uniswap. Current solutions fall short in two ways: they either require approval from a centralized set of validators or shift security responsibilities to applications. This latter approach still results in a need for approval, whether from centralized or decentralized actors.
We propose a solution to this scalability issue by introducing the first permissionless bridging protocol. The core principle is to allow any participant to join the bridging protocol without approval. The key to solving this problem is to have consistent security assurances implemented by the protocol itself. Security should not be delegated (as with DVNs in modular security solutions) or rely on third parties (like validators in blockchain of blockchains). Instead, security should be ensured by a cryptographic protocol (homogeneous security).
We leverage the concept of Atomic Swaps, which allows two parties to exchange assets trustlessly. This technology is the core of the Lightning Network but is not yet practical for cross-chain swaps. We introduced improvements on top of the original Hash Time-Locked Contracts (HTLCs), such as PreHTLC, Atomic Pools, and a 1 tx + 1 sign flow, which make the solution usable for cross-chain swaps.
This technology allows any two parties to exchange assets on different chains. Specifically, the two parties are the user and the liquidity provider. Users send requests to liquidity providers, who fulfill them using Atomic Swaps. There are no third parties or gatekeepers; the security of the exchange is fully ensured by the cryptographic protocol.
What does this mean in the grand scheme? It means that any new network developer can deploy the V8 contract to their network, find a liquidity provider willing to exchange assets with users, and voilà—anyone can now bridge to this network.
The Layerswap Protocol (V8) is currently deployed on all major network testnets, including EVM-compatible chains, Starknet, TON, Solana, Aptos, Sui, and Stacks. To try it out, visit https://layerswap.io/v8. For more technical information, read the technical blog post, refer to the protocol specification (draft), or explore the source code on GitHub.